MonteCarloSS.com

Rear 3-link

Posted By: MC96

Rear 3-link - 03/20/20 02:45 PM

Im bored and fingers crossed going on unemployment soon, so in the spirit of Bobs spring thread and the other well written stuff on here, lets see if I cant string some cohesive thoughts together. Similarly in the spirit of the board feel free to jump in, none of that "stay off my thread crap" I see elsewhere.

If you follow Travis on here or Facespace you'll know he is putting a narrowed s197 8.8 in his monte. The goal is to allow more rear articulation with some other side benefits for his autocross habit. A Mustang 8.8 of that vintage has a single bushing, whos pivot its parallel to the rotation axis of the axles, right on top of the center of the housing.

Its been well documented that 8.8s are a nice fit for G bodys. Seemingly as popular as the 9" from what I have seen. There is plenty of info about triangulated 4 link donor FoMoCo cars for bolt in options. A direct swap doesn't really address the inherit compromises a 4 link that is somewhat bound up by design.

So Travis can chime in with better details, but its a 31 spline torsen dif, large brakes which Im sure there are plenty of proficient stock options for through the trim levels of the stangs. I re drilled rotors for him to be able to fit on custom, shortened/redrilled axles. The plan is to put standard circle track street stock multi hole lower control arm brackets on it. Lateral control will come from a panhard similar to any 3rd or 4th gen Camaro, with height adjustments on either end to adjust roll center.

The main issue he tasked me with was mounting the UCA, a problem that guys installing watts links are having to figure out as well. The factory 4 link system locates the roll center through the triangulation of the arms as demonstrated here
[Linked Image]
With the addition of a panhard bar, or watts link you are adding a second roll center location, which in theory binds the compression and extension of the rear suspension. In practice stamped control arms twist, and rubber bushings can absorb an amount of the force trying to stretch or shrink a control arm and comply to prevent a total lock up. If one were to have all rod end tubular arms the issue would be magnified.

In one of Lances old posts he talks about a poor mans 3 link, much like unhooking a panhard bar it frees the rear to "shuck" back and forth freely the rear no longer has a roll center and needs a panhard bar / watts link. Heres the video https://www.youtube.com/watch?v=EDM9_-4kjHg&t=10s

With the top link at such an angle it creates an odd articulation arc that wouldn't allow cornering in two directions to be the same.

My thinking is with the top link at a 45 to the panhard as viewed fro above it would almost act like an anti squat when the LH is being compressed but a pro squat when the RH is being compressed (assuming the panhard is set up like most cars, rear end on the LH frame mount on the RH) as opposed to being 90 degrees to the panhard and only mathematically effecting anti squat as calculated from a side view. Whether or not that would even be felt is probably a better question.

The goal is to have something that bolts in, as far as I am concerned that should also mean no drilling holes. The preliminary design is something that uses spacers in place of the UCA bushings in the stock mounting holes, then connecting between the two of those with a tube that has a multi hole mount for anti squat adjustment. Here is a rough drawing in Mastercam.

[Linked Image]

Originally, with the worry that pushing / pulling forces on an offset hole would try and rotate the assembly I made the bushing inserts as large of an OD as possible, as an added measure I planned on using two bolts to jam against the back side of the rear cross member/ bulkhead. This was the plan until I got under my frame and saw the triangle/ trapezoid plate that goes from the bottom lip at the center of the bulkhead to the top lip. It also has two holes in it already The above drawing doesnt reflect that but it will.

Hopefully I write in a way that is easily followed, at least you dont have to read it in my handwriting too.


Stay safe!
Posted By: SSLance

Re: Rear 3-link - 03/20/20 03:37 PM

I know two people that have home built 3 links where triangulated 4 links used to be and both are pretty successful (I've raced both cars). Both were compromised builds (kept rear floor intact) so not ultimately perfect but still better than OEM.

Is the S197 upper link mount directly in the center of the axle? Is there a way to extend the axle mount rearward to make the upper arm any longer if possible?

I like the idea of making a mount to incorporate the OEM frame side mounts but realize it may make the upper arm uber short.

Can't wait to watch this progress...
Posted By: MC96

Re: Rear 3-link - 03/20/20 04:10 PM

Im not sure if it is centered above the axle or not, both viewed from the side and viewed from the top. Its close though.

When Travis and I first spit balled this I had a rod like below in mind. Dirt modifieds bury the RF so hard (with lots of caster) you either have to notch the frame for the tie rod or run a TRE like below. I thought that may be a good option to just bolt that into the LH or RH upper bushing location on the frame. Would work perfect for an offset upper link. Theres a formula out there involving torque multiplication through the driveline that optimizes upper torque link location on the rear end offset to the right.

[Linked Image]



I agree longer is better. but I dont know if there is a way to do that and maintain a truly bolt on approach.
..... other than incorporate the upper mount rearward onto the housing cover...

The stock uppers are ~11-1/4, but at a 45* angle so the effective radius they travel as viewed from the side is 8", which in my mind is about what I thought the upper arm would end up being. Im thinking the lowers are 19.25 and a 45 degree angle in relation to each other, 22.5* from centerline, making the effective arc about 17-3/4. Over twice the length.

On compression, once the forward mount of the upper is below the rear end mount it will gain negative pinion angle quickly, which supposedly gains bite. What I dont want is a static downward-from-the front upper angle that changes through travel to the opposite, meaning pinion angle gains positive then rapidly gains negative. I also get our dirt stuff in my mind with large travel numbers so this may not even be an issue. That all said, pinion angle gain shouldn't be any different from stock based on the geometry described above.

I made a deal on one of these yesterday.
https://www.portcityracecars.com/WATTS-LINKAGE-ASSY..html

Watching your video in the past Lance I started to realize with my notch it was still going to be a crapshoot for even 315s let alone the 335s I want to run. The cambered rear coupled with the staight up and down articulation of a watts should help take guesswork out, its still going to be close. Now I need a way to put my top link in as well. Materials are cheap so I may copy it for myself. although the eventual goal is a decoupled top link.

[Linked Image]
Above is the answer for making my top link longer, The slot ends up being straight up and down so you can picture how far it hangs off the rear.

Curious to see how the people you mentioned accomplished the task.
Posted By: Travis Jones

Re: Rear 3-link - 03/20/20 05:29 PM

Originally Posted by SSLance
I know two people that have home built 3 links where triangulated 4 links used to be and both are pretty successful (I've raced both cars). Both were compromised builds (kept rear floor intact) so not ultimately perfect but still better than OEM.

Is the S197 upper link mount directly in the center of the axle? Is there a way to extend the axle mount rearward to make the upper arm any longer if possible?

I like the idea of making a mount to incorporate the OEM frame side mounts but realize it may make the upper arm uber short.

Can't wait to watch this progress...


The stock upper arm on an 05-10 mustang is 8.5 inches, ~9 inches on 2011-13. Seeing as the S197 is one of the best handling stick axle platforms out there, while I agree a longer third link IS better, I'm not sure it's required, considering the limited vertical axle travel in the application. The short upper link does take some dialing in as far as the angle goes, but if the BOSS 302 guys can make their cars go around corners, so can we.

The plan is currently to use UMI lower boxed Roto-joint lowers for maximum articulation and an UMI 05-10 upper with the roto joint on one end. I have circle track multi hole lowers to weld onto the axle tubes. I'll be using C5 wheels with a deeper offset to make sure the stock ford brakes clear the frame (the caliper itself clears, but there are levers and brackets for the integrated parking brake)

I've also got a circle track clamp on style adjustable panhard rod bracket, and a Multi-hole bracket on the frame side PHB mount.

To clarify one point Mason made earlier, the S197's only came with Torsen diffs if equipped with the track pack, but every GT came with a ford Track-lok, That's what I plan on running for now, but I may spring for a T2-R. They all have 31 spline axles, and the center bushing is dead center in the diff, almost in plane with rear cover.

The overall length of a S197 rear end is 65.5 inches wheel mounting surface to wheel mounting surface. My new wheels fit with 2.5 inch adapters on the stock axle, If we assume the stock rear end is 58 inches end to end +5 brings us ~63 inches. So I'm thinking I'm stuck shortening it 1.25 inches per side, with custom axles
Posted By: MC96

Re: Rear 3-link - 03/20/20 05:45 PM

I knew I was off a little on the specs.

Talking about splines

Copied and pasted from a post I made elsewhere using info I found in a book years ago.

....

Axles are on a 24 pitch spline, meaning 30 splines is 30/24ths of an inch, or 1.25" That also means a 28 spline axle is 1.166.

Axles also supposedly gain 1% strength every .002" of diameter. By that math a 30 spline is 42% stronger than a 28 spline axle.

According to that math (if I did it right) , a 31 spline axle (like most ford 9"s) is 104% stronger than a 26 spline 10 bolt, 35 spline is 188% stronger than that same 10 bolt.

....

Of course that doesnt speak to the advancements in metallurgy or the differences in materials in general.
Posted By: Travis Jones

Re: Rear 3-link - 03/20/20 05:57 PM

Originally Posted by MC96
I knew I was off a little on the specs.

Talking about splines

Copied and pasted from a post I made elsewhere using info I found in a book years ago.

....

Axles are on a 24 pitch spline, meaning 30 splines is 30/24ths of an inch, or 1.25" That also means a 28 spline axle is 1.166.

Axles also supposedly gain 1% strength every .002" of diameter. By that math a 30 spline is 42% stronger than a 28 spline axle.

According to that math (if I did it right) , a 31 spline axle (like most ford 9"s) is 104% stronger than a 26 spline 10 bolt, 35 spline is 188% stronger than that same 10 bolt.

....

Of course that doesnt speak to the advancements in metallurgy or the differences in materials in general.


Also of note, even the factory ford axles shafts taper down at the spline, the spline is the thinnest part of the axle, at the axle end i think the bearings are like 1.6 inches.
Posted By: MAP

Re: Rear 3-link - 03/22/20 09:19 PM

A few thoughts:

1. A 3-link stick axle has been bandied about for at least 17 years here, so there's a long history of discussion. It definitely has attractive features about it, and if the UCA rear mount can be mounted right of center, even better.

2. Mounting the UCA rear pivot to the rear of the axle CL for packaging a longer arm is a very worthwhile goal.

3. The closer the UCA and LCA side-view swing arm lengths match, the more linearly the rear will behave with vertical suspension motion, so anti-squat/anti-dive will remain more constant. However, non-linear action may be desirable.

4. The strength of the rear is dominated more by pinion gear diameter than ring gear diameter, despite a long history of popular perception that the opposite is true.

5. Is the "poor man's solution" simply removing one of the two 4-link UCAs to avoid roll center conflict? Terrible idea, in my opinion. Anti-squat/Antu-dive create reactions that tend to put the body in roll, and unevenly load the rear wheels.

6. Marcus (Mark Savitske) marketed (markets?) a Watt's link where he claims that the stock rear's compliant bushings allow the Watt's link to dominate roll center location.

7. About conflicting roll centers, yes, the binding tendency is a function of the vertical separation between theoretical centers. What the video misses, however, is that the separation varies as a function of vertical suspension travel. Best to do everything possible to eliminate any binding tendency from the get-go.

8. 96, in that CAD rendering, is it the intention that the forward UCA mount slides laterally on that short tube to avoid roll-center binding as the vehicle rolls? If so, I doubt that bearing arrangement will live long, because the race will tend to get dirty and interfere with the intended motion. That bearing must have extremely low friction to work well; but good thing that the CAD rendition shows a rod link there.

9. Herb Adams' idea of a Satchell link rear would do a great job of reducing the stock's towering rear RCH, but too bad packaging it is so difficult. A 4-link does have the advantage of keeping moving mass lower than most 3-link alternatives.

HTH,
MAP
Posted By: MC96

Re: Rear 3-link - 03/23/20 02:50 PM

No lateral movement of the heim, The bushings taper down inside the rod end, the shoulder keeps the rod end from moving L-R.

If we can figure the exact (or within 1/2") location of the upper link, I render the bolt holes on an arc that allows the heim to be moved up and down with no static pinion angle change with bar angle change.

Unrelated,

I have lower mounts designed with the same intention for circle track applications but relies on knowing the ride height of the front side of the LCA to plot the arc accurately. The stock lower mounting hole is approximately 2-3/8ths below the axle tube. One sanctioning body allows the hole to be a max of 7.5" below the housing tube, and thats assuming a 3" ford 9" tube.

Think about how much rear steer that would induce on a car like the one in my profile picture with the LR at full droop and the RR compressed to the point of the lower being level with the ground. (The was nothing level about the "ground" Kokomo that day, more like a chisel plowed field)

Posted By: MAP

Re: Rear 3-link - 03/23/20 09:37 PM

So, let me make sure I understand correctly. I'll use the usual x,y,z vehicle coordinate system.

Your CAD rendering of the UCA shows the rear mount with freedom to rotate about y only, and the front about x,y,z. Translation is constrained in local x,y,z at the front and rear mounts. If so, then the UCA completely constrains the rear's roll center in a manner that's very similar to the existing 4-link design. Is that correct, or am I missing something?
Posted By: Travis Jones

Re: Rear 3-link - 03/24/20 03:25 AM

Originally Posted by MAP
So, let me make sure I understand correctly. I'll use the usual x,y,z vehicle coordinate system.

Your CAD rendering of the UCA shows the rear mount with freedom to rotate about y only, and the front about x,y,z. Translation is constrained in local x,y,z at the front and rear mounts. If so, then the UCA completely constrains the rear's roll center in a manner that's very similar to the existing 4-link design. Is that correct, or am I missing something?


It's essentially a copy of the 05-13 Mustang rear end suspension geometry, which we know works around a race track.
Posted By: MAP

Re: Rear 3-link - 03/24/20 03:46 AM

Hi Travis, I'm not familiar with that suspension. I come back to my question for 96 as I asked it.
Posted By: mmc427ss

Re: Rear 3-link - 03/24/20 05:58 AM

I'm following this discussion, improving the rear grip has always been of interest to me. Pretty familiar with most of the ideas to improve the lousy rear roll center, just not educated enough on the subject and not willing to cut up the car to do what's necessary to install 3 link. Also have an 8 1/2" which make a 3 link a little more difficult.
BMR has a three link for a 12 bolt rear that puts a whole new spin on using a Salisbury rear. But looks like it weighs a 100 lbs
https://www.bmrsuspension.com/index...ncatid=25&catid=77&productid=231
Not everyone is running a 9" which allows easy welding of new steel to the housing. A cast iron centersection makes things more difficult.

Way back in the day Kirbin duplicated the GNX rear three link setup for the 8 1/2". I was at one of his open houses and watched the GNX rear suspension being welded into a GN, pretty cool. The length of the 3rd arm, who know if it was really a plus for handling and was it really a plus for traction, or neither, but it was cool. Kirbin had already installed that GNX 3rd arm into his pristine T-type parked at the door which I drooled over.

Have done some thinking about the FAYS2 watts link. But I don't like the way it installs into my car, tailpipes, the clamps on the rear to hold the links, it's size. Would like to find one for cheap so I can cut it up and clean up the install a lot by doing weld in place instead of bolt in. .
http://www.fays2.net/fays2_watts_link_23_.html

Will follow this thread and learn some.
Bob
Posted By: MC96

Re: Rear 3-link - 03/24/20 02:47 PM

Doing this on mobile, chrome doesn’t like the scaling of the website so forgive any mistakes.

The rear has a single bushing on top mounted like a pedestal, rubber with a steel sleeve similar to our stock upper bushing mounts, just with different dimensions.

If we assume it will be parallel to the vehicle Y.

X rotation will take place at both the bushing pivot and heim pivot, as views from the side.
Y rotation will be mostly taken care of within the heim, although if this was to be maxed out the rear bushing could absorb some.
Z rotation should be minimal, but depending on the instant center of the rotation the heim or bushing should articulate accordingly.
Posted By: MC96

Re: Rear 3-link - 03/24/20 02:59 PM

[img]https://ibb.co/T0y17fY[/img]


Very rough first piece. Like “didn’t have any 1” tubing so used sch 40 poo pipe” rough


Bob, I’m sure by definition the torque arm stuff is a 3 link but I have always put it in its own category. Probably because of the circle track stuff.

Dirt late models use a “lift arm” in which there is a coil over at the front end, the suspension mounts to the rear with birdcages that float therefor any toque seen on the rear end from the pinion climbing down on the rear of the quick change ring gear is transferred to that coil over assembly. There is also a “brake chain” limiter that sees tension on deceleration with a “6th coil” on it. Many modifieds use the same set up but sanctions such as IMCA require that mods use a pull bar. So while they are both 4 links with cages the pull bar and lift arms are really different. Lift arm compresses on acceleration, pull bar extends.

The only think I have really seen as far as a 3 link (asphalt mostly) torque arm/lift arm would be the nueline suspension arm, which is a cool concept
Posted By: mmc427ss

Re: Rear 3-link - 03/24/20 03:16 PM

https://www.neulineco.com/neuline-rear-suspension
Bob
Posted By: MC96

Re: Rear 3-link - 03/27/20 06:24 PM

Dang messed up the image insert on the last post. Probably user error but that was my first mobile attempt.

Anyways. Watts up? (Usual disclaimer: ignore the mess)
[Linked Image]
[Linked Image]
[Linked Image]
[Linked Image]
Posted By: MAP

Re: Rear 3-link - 03/28/20 02:31 AM

Interesting 96! Seeing that quick-change rear, the layout of your bracketry finally makes sense to me (somehow I missed that before.) May I ask how you like that rear if it doesn't deviate the thread too far? Is it reasonably quite? Weight compared to more popular rears? What about that bellcrank clearing the chassis with full suspension travel? Also curious about the purpose of those upper links: camber/caster adjustment? Thx.
Posted By: MC96

Re: Rear 3-link - 03/29/20 02:11 AM

With the disclaimer that I know many people are in a bind or worse right now I have to say that I am LOVING the time off. Work is paying us for 2 weeks then it’s unemployment from there, I’m set on my bills and if I can’t go to the races or the bar I don’t have any other expenses. Just time to tinker with my projects.

So the QC is one I have had forever, was a “fresh” one that somehow needed completely gone through, same old story. It’s an older one still (as far as I know) dimensionally true to the hallibrand stuff. The main difference from the newer stuff being that it has a deep rear cover, not an extended rear cavity and flat cover like all the stuff nowadays has. Winters still makes one like this they refer to as “heavy duty” but is probably marketed towards the street rod guys because it isn’t anodized and has a cast finish. This one is a Benson. Johnny Benson Sr still has a speedshop in Grand Rapids and picked up the phone when I called about a bearing number. The phone number is actually cast into the side bell.

It’s a magnesium center, side bells and rear cover as well. Aluminum tubes with a bolt on floater flange at the end, the snouts are both 1° on it right now and I rotated them a little to be a mix of toe and camber. I keep a look out at all the swap meets for other snouts, there are 0-2.5° in half degree increments. Below 1° you can just use crowned floater axles but above that you need cambered drive flanges, something else I always have my eye out for, new they’re about 300$ but I’ve found 4 used so far cheap. I’m told they wear so I’ll just keep looking. The friggen joe Gibbs grease for drive flanges like that was 50$ for about 16oz..

I put a new 4.96 r/p in it and actually traded a spool for a detroit locker to local dirt late model guy that isn’t allowed a dif. So I put new red springs in it just because that’s what lance has. All new bearings, a lower shaft, and gun drilled axles. DTS in ionia mi set it up for me

The hub are modular aluminum made by Acro tech, sold by allstar and others. Joes makes hubs that are dimensionally the same as well. I made the floater plates, the rotors are used short track cup car front rotors made by AP, the pair on the rear both say “Bristol 31 car”. The bobbins are Alcon but I modified them, I made the floater plates at work, they have about .010 float. A guy posted on a fb group “hey I have a buy 500$ get 500$ free wilwood certificate who wants it” well I guess it was my day to be lucky.
Radial mounted superlite 4 pistons. The rotors are 12-7/8” so I had to use some spacers but other than that it works good.

I have some DRP bearing spacers in right now and they free up a ton of friction. I put daylube grease in the bearings too, another not so cheap thing but supposedly worth it.

Some other tings I did was paint the bare mag with eastwood radiator rattle can, supposed to help with heat transfer. I did the standard circle track thing and put fittings on to remote mount a full can so I don’t have to squeeze gear lube bottles into the side bell under the car, just fill a quart or so overflow tank style reservoir in the trunk area and it drains into the case. I also bought some Admax RGO #3 gear lube through franklin. Supposed to be the cats xxxx , better be for 20$ a quart

The bars you see are support braces, allstar sells the individual pieces needed. I don’t think it shows up in any pics but therme is a matching set of bars clocked 180° on the rear. Asphalt late models use them on the right side because supposedly the load will move things enough to change camber. Curiously I have never seen them on a dirt car.

I probably have into this one what a brand new bare bones steel tube no camber rear would cost so I suppose I’m money ahead. It’s been a project for sure. Further upgrades would be microblue or ceramic hub and dif bearings, rem polished ring and pinion and lightened/polished spur gears. I think at that point it might be worth it just just buy a center from DMI or winters and press my tubes into those bells.

They make helical spur gears that are “quiet” I’ve only ever seen one set in person so that’s a 500+:1 ratio.
It’s going to be loud as hell, any in car circle track video you can hear the gears screaming but I guess that’s something I’ll have to deal with, I’m sure akin to a gear drive timing set.

As far as weight, it’s close to a 9”. People think they rob power having to go through a second set of gears but the ring and pinion actually has no hypoid dimension, just a standard spiral bevel, they dyno within 1.5% of a 9” (which itself does have a high hypoid which robs some power but that’s where it’s strength partially comes from)
I’ll drag the bathroom scale out there tomorrow and weigh it because now you have me curious.

The bell crank may clear, I’ll know soon enough.

What’s interesting to me is, after almost 100 years of these things, apart from little things almost every part interchanges between brands.

All the local metal suppliers are shut down right now but I may order online to keep progress on Travis’ part of this going.
Posted By: MC96

Re: Rear 3-link - 03/29/20 02:13 AM

I’ll add some links to all that I mentioned here when I’m back by my desktop.

Hope everyone is safe and stays that way
Posted By: mmc427ss

Re: Rear 3-link - 03/29/20 06:37 AM

I'm glad I'm not the only one to do lengthy posts.
Interesting rear setup. Have never been around one of them. Lots of good parts. Should be a light weight unit, my guess is 155 with brakes.
Bob
Posted By: SSLance

Re: Rear 3-link - 03/29/20 01:47 PM

Wish I had the parts, or even a direction to go with my car project right now. I'm stick doing home improvement projects.

Love the housing, should be interesting to see how it fits under the chassis. Love the outside the box thinking...
Posted By: MAP

Re: Rear 3-link - 03/29/20 08:39 PM

Speaking of thinking outside of the box, if we could just shift an MCSS's center of mass significantly rearwardly, then a good IRS would solve all these problems. I'm amazed at the trials and tribulations we go through to try to band-aid an old, tired factory configuration. Many times, although admittedly certainly not always, it's better in the long run just to ditch the old design and start afresh.

When I look at current design thinking in the realm of ICE motors, if I could take an MCSS body and drape it over a C8 powertrain, I'd be super happy.

Anyway! So I like the copious amounts of magnesium in that rear, 96. That's got to be worth some serious coin.
Posted By: MC96

Re: Rear 3-link - 03/29/20 09:21 PM

Here are some links

Watts
Hardest snap ring install of my life

Tubes
I think my old roommate gave them to me, knowing him he must not have known what they were worth

Snouts
The last swap meet I went to I got a box of 4 snouts for 40 bucks.

Drive Flanges

Hubs

Gear Chart
120+ plus combos 2.56:1 to 9.14:1

Bearing Spacer

I cant seem to find a link for the rotors, but they are AP CP4770-114GE & CP4770-115GE

Remote fill can



I'll see if I cant get it weighed today.
Posted By: MC96

Re: Rear 3-link - 03/29/20 09:26 PM

Its certainly fun to take a lighter to any shavings that come off the rear.

I forgot a brakes link, I have a pair of fronts and rears.

You mentioned IRS

Sikki makes kits to install Winters "skull and crossbones" centers with IRS side bells into various imports for drifting.

Looks like they about double the price on them.. yikes.
Posted By: MAP

Re: Rear 3-link - 03/29/20 11:28 PM

Hi 96,

Yes, magnesium can be pyrophoric. Flashbulbs of old were filled with magnesium wire to create that brilliant bluish-white light. Always keep the ratio of surface area to volume very low if you want to avoid a fire hazard with Mg.

Those prices were a shocker, 96. Seems I need to double the prices I remember across the entire board. Quick-change IRS: seems like it's pushing $10k for a complete rear setup. Crazy! As I predicted, this hobby is headed for extinction...

Btw, I'd encourage you to keep up that CAD work and the idea of making/selling your own parts!

Best,
MAP
Posted By: MC96

Re: Rear 3-link - 03/31/20 08:43 PM

Just gotta be frugal!

Bob, 218lbs with everything but brake lines on it, it looks like 9"s are pretty close to that.

I should have quite a bit let rotating mass compared to a non floater 9" with the advantage of some friction free'd up and strength on top of that.

The other thing I didnt mention is wheels.

I could've went with Howe hubs, or even a Coleman with a 5 x 4.75 pattern. When you're scrounging used stuff like me though those just aren't common. Those only come with the standard 8x7" rotor pattern, wilwood makes a 13" rotor on that pattern but I was not paying $400+ for a pair.

Even with that hub, the drive flange is 80mm OD so finding a wheel with the correct back spacing, width, center bore, and my chosen diameter (18") was going to be a chore. Especially wanting 315s or 335s in the rear.

Originally I was going to have this rear done by last August and Travis was going to put it in his car for some miles and autocrossing. Partially so if there were any issues they were immediate and it could go back to DTS, and so Travis could play with ratios. (Offer is still open btw)
DTS took longer than I anticipated, and I drug my feet a bit too long for any fun last year.


Travis is on 17"s with a cheap auto X tire, I found a set with the nipples just barely worn off on eBay and bought a pair. And realized we could probably use Impala SS wheels. So I found a cheap pair in-state. Those are currently at the powder coater getting turned into an SS-stripe-maroon type color. I think once I'm out of quarantine I will pick another pair up so I can have a set of cruisin wheels/ tires and a set of race wheels. Amazingly the Impala wheels fit the 80mm drive flange OD perfectly, the backspace is yet to be verified but it is close.

Travis can chime in with the tire specs, Im thinking 255/50r17. Im excited to see those wheels under a Monte, always had a soft spot for the Impalas.
Posted By: MC96

Re: Rear 3-link - 03/31/20 09:07 PM

Forgot to mention the clearance around the pinion.

A few years back IMCA started allowing their modified division to run quick changes as they were the lst sanctioning body requiring 9"s left. Fast shafts realized that instead of all these guys having to buy new driveshafts they could just offer a 1" longer yoke for a QC. Thats whats on it now.

So in theory my rear u joint should be in the exact same position as with a 9". I happen to have a friends rolling chassis with a 9" sitting in my other bay so I'll check that out tonight.
Posted By: MC96

Re: Rear 3-link - 04/02/20 02:47 AM

Got some stuff ordered for a final piece today. Hopefully I can stay busy this weekend and get it done for Travis, I'm sure he is stir crazy in Detroit right now.

Once the bar is built I need to take some measurements to draw up the steel plating so I can bolt it into the frame.


I got a chance to measure around the 9" yoke.

The center of the pinion shaft, at the u joint upward has 7.5" to the rear frame firewall/crossmember at stock ride height.

The propeller from the center to the most outward "points" is 4.5"

So at most from stock ride height I have 3" of travel.

Which since I want it lower is problematic, but I also do not plan on much travel. A stiff bump spring on the rear shock shaft might be added insurance. Some torch and hammer time isnt off the table.


DPI, now Larsen Racing Products makes a rear watts like mount for a quick change, its adjustable which is nice. The unfortunate part is that its designed for the newer, more common, flat cover quick changes. I have never personally seen a roundy round car with a watts. Although through research one chassis builder of the "touring style" nascar whelen modifieds use a watts but it is mounted to the side of the pinion plate, not in the center. Howe chassis TA2 cars are offset like that, whereas the Port City cars use the piece I have. The offset mount is quite a bit cheaper

So other than the fact that I cant use it on the QC I currently have, and that it would probably be impossible to find used I dont know that I would want to have to pull it all apart to have to change gears.

Hope everyone is staying safe.






Posted By: mmc427ss

Re: Rear 3-link - 04/02/20 11:08 PM

While in house lockdown to a large degree, we're old people, have had way to much internet time. Even have the flower beds done and the vegetable garden ready for planting the Victory Crop. Did a long post on the rear spring topic but decided to spend time typing on this post, will dump that one on the forum later after the car is out for a drive again, maybe soon I hope.
While I'm committed to no cutting on the chassis to add a third link the Watts has had me interested for years. There are numerous bolt in available for many applications including the FAYS2 for the G-body. My problem with them is the bulk of material uses, how it attaches to the rear tubes and exhaust/tailpipes clearance.
http://www.fays2.net/

There are several cleaver ways they have found to use a spicer type rear cover to adapt a mount for the watts pivot point. BMR has this:
https://www.bmrsuspension.com/?page=products&productid=232&superpro=0
Although for a 12 bolt it's the concept and way they attach to the rear cover bolts. Also would think with the length of the 3rd member it's about IC for weight transfer.
Several other versions available from Whiteline:
https://whitelineperformance.com/collections/watts-link-kit
And similar but more adjustable is the Cortex:
https://cortexracing.com/suspension/watts-link/
Both of those application are for the late Mustangs but the idea is there.


Funny, was watching some videos of watts links and found out a Chrysler PT snoozer uses a watts in the rear. Not so much for the handling but to keep the rear from falling out the side. Also PT is only a two link suspensions via a short truck arm type link and a little fixed watts to do the rest. Interesting, simple setup. Being FWD there is no pinion angle to deal with as the rear suspension articulates.

Have seen a few clever guys weld up a pivot mount for a 10 or 12 bolt spicer patterns, one guy even made one for his Dana 60, attaching around the case cover and fabricated a pivot point. On my 8 1/2 an LPW girdle has been installed for years, it has two holes for the tube supports that may be able to be used as additional strength on a spicer install. Buying a new HD girdle and have more material added to it is not out of the question, it just a chunk of alum that can have additional alum added. As another piece of my rear suspension's on going development the watts has been kicked around. Just need to figure out how to incorporate it without taking up all that space it would need.

In case we have forgotten there is another member here doing a 3 link and watts. Justin hasn't been heard from in a while, hope he's still making progress on that frame.
http://www.montecarloss.com/community/ubbthreads.php?ubb=showflat&Number=1055617&page=4
Bob
Posted By: MC96

Re: Rear 3-link - 04/03/20 02:47 PM

I have seen the BMR, and some various Mustang ones but not the adjustable one. I agree that I like the idea, spending Travis' money for him I would have him get one.

I saw the PT watts on rock auto, there are some other Mopars that use it as well, I was trying to find a cheap propeller.

Im thinking a webbing of some sort could be made on the plasma table that welds onto a stock cover, it could easily protrude above the housing to include a top link mount and even a pivot for a watts, maybe that could be the 2nd half of a true bolt in kit, using a stock rear still.
That, or, I'm actually a pretty good aluminum TIG welder, once I'm back at work some billet mounts could be added to an old aluminum cover. I'll have to keep an eye out for one cheap.

The rear cover mount vs the frame mount is an interesting thing.

Mounting on the rear means no roll center movement when the rear of the vehicle changes ride height, although your c/g is changing with the car so your moment arm is changing length.

Mounting to the frame means the roll center is pitching with the c/g so your moment arm is the same throughout travel.

Whether or not anyone would ever notice a difference is probably the actual question to ask.

My thinking when looking at all these kits is that the producers goal is to "put a watts on X" so packaging has determined where it gets mounted. I would look more towards the OEs and see how they have mounted watts' on RWD applications when they had a blank slate. I know the Panther had them in later years but being a late addition to an existing platform I'm not sure that platform is the best measure. They mounted them to the rear, for what its worth.
Posted By: Hunter79764

Re: Rear 3-link - 04/03/20 03:34 PM

I know some of the Durango SUV's have Watt's links mounted to the rear cover. Looks like they use a beefy, cast cover. I'm with you that with some clever fabrication, you could create a 3 link/watts combo mount that would go over the diff cover on a stock style axle (or between the cover and the housing, like a spacer, and use 2 gaskets). Making it for an Explorer 8.8 would give a plentiful housing source, reasonable strength in stock form (I think a bunch of them came with TracLoc and 31 splines?), and taking ~3" out of the longer side (it has an offset center) to match the shorter side puts it close to the Gbody width from what I remember, and you can use 2 short side axles on a budget. Would that put too much stress on the cover bolts? I don't know, but I'd think we could collectively figure that out.
Posted By: MC96

Re: Rear 3-link - 04/03/20 04:26 PM

There is a user on the gbodyforum that has done something similar, he used I think a blazer zr2 rear if I’m not mistaken (30 spline axles I think?) and did exactly what you described, sandwiched it and used two gaskets.

His maintained the stock triangulated 4 link geometry, but the idea transfers to any integral housing rear end with a back cover/ any torque link. Could also put “ears” on it similar to the BMR 12 bolt mount Bob shared and stand off a watts propeller as well.

Maybe that’s the ticket. I’ll have to see if I can’t find a DXF of the cover patterns for the different rears. It would be a good project for the table.

I’ll link the gbodyforum member when I’m back home.
Posted By: Hunter79764

Re: Rear 3-link - 04/03/20 07:18 PM

I didn't look closely enough at the BMR setup, but I see that now. It also has me thinking of the 4 link mounting ears, which would be the simpler setup vs the fabricated truss/arch design I'd considered before to installing an 8.8. Basically, I'm too cheap to do a 9", and too cheap to buy a Fox 8.8 installation kit. Trying to get the upper mounts figured out on an Explorer rear is the direction I'm leaning towards most. Different animal from what you have on your plate, but you are inspiring me to look in a new direction.

I'm the kind of guy that would much rather dwell on something for hours/days/years, then maybe one day get around to making it out of scrap and a $100 bill on sale day at U-Pull-It. This has potential smile
Posted By: Travis Jones

Re: Rear 3-link - 04/04/20 12:37 AM

Originally Posted by MC96
There is a user on the gbodyforum that has done something similar, he used I think a blazer zr2 rear if I’m not mistaken (30 spline axles I think?) and did exactly what you described, sandwiched it and used two gaskets.

His maintained the stock triangulated 4 link geometry, but the idea transfers to any integral housing rear end with a back cover/ any torque link. Could also put “ears” on it similar to the BMR 12 bolt mount Bob shared and stand off a watts propeller as well.

Maybe that’s the ticket. I’ll have to see if I can’t find a DXF of the cover patterns for the different rears. It would be a good project for the table.

I’ll link the gbodyforum member when I’m back home.




Also the chevy cruze of all things used a watts link, except the eco. lots of front wheel drive stuff with a twist beam axle does.

As for the watts link discussion, I'm not terribly interested in putting a watts link on the car. It's much more complex a system than I want, and the failure mode of an aluminum diff cover housing in the event you curb a car not that hard scares me. Much like Lance's, build my car is is a street car that occasionally races. An adjustable panhard rod will be fine for my purposes. Now for an all out race car that would be the ticket, but I'd also do a few different things, longer 3rd link, notch the frame, etc.

This is supposed to be a mostly bolt in endeavor.
Posted By: mmc427ss

Re: Rear 3-link - 04/04/20 05:28 PM

Yesterday after pulling the alignment "rack" from under the car took a look again at the confines a watts would need to go into. No way without massive tailpipe mods would a Fays2 or a diff cover application fit with tailpipes. If you look at a lot of the watts installs there are no tailpipes, just muffler turndowns, One install I saw had the tailpipes routed under the watts and then back up again to exit behind the wheels, looked like a kitchen sink trap and I would suppose a good place for condensation to get trapped. Some WOT out on the highway would clean it out, just hope there are no other cars on the highway behind you.

Spending a lot of time looking for other watts applications you find dozens of car manufactures that incorporated a watts into the rear suspension. You find dozens of guys that have added a watts to the rear suspension on race cars. But what you find little info on is the design of the watts to get the max benefit for cornering. I get the advantage of the side to side travel of the rear that the watts has over a panhard bar, but the actual math involved in making an adjustable watts setup that is hard to find. With the factory installed watts they come in every conceivable location from the back on the diff cover to the top of the housing and even on some race car located on the bottom of the rear housing. But all are intended to control side to side movement but with regard to roll center impact they seem to look only at packaging and not improved roll center. So while it nice to see everyone adaptation of a watts how it effects roll center always seems to be something not talked about much except in a very few instances. So designing something to fit and be adjustable is difficult and why the Fays as a bolt-in seems the easy choice, but at the expense of real estate.

Will continue to look at improving the rear via watts of panhard but it's the 10 lbs into a 5 lb bag that is the hardest part, adjust-ability is a whole other thing.

Here's Monte build that Justin has been working on although we haven't heard from him in some time. But it's a G frame with 3 link 9" and watts. Pics at the bottom of the page 4. Would be nice to hear from him and see if the project has moved forward since his last posts.
http://www.montecarloss.com/community/ubbthreads.php?ubb=showflat&Number=1055617&page=4
Bob
Posted By: MAP

Re: Rear 3-link - 04/04/20 09:42 PM

I think if you search back 10(+) years when the discussion style here was a bit more theoretical, you can see some discussion about whether the roll center should remain fixed to the live axle, or fixed to the chassis. There are pluses and minuses with both. Personally I think the difference is usually unimportant, because we tolerate lots of front RCH migration with the stock front-end design.

One feature that I've written about but haven't seen anywhere else, is how unsprung mass is influenced by RCH when the suspension is put in roll. Basically, if unsprung-mass movement directly couples with sprung-mass movement, then a portion of the sprung mass will reflect back to the unsprung mass. Think of the unsprung and sprung masses as if they were sitting on the ends of a seesaw: the location of the fulcrum is critical for determining the mass reflected to either end. So, for the rear, decreasing RCH is good: it's just like moving the fulcrum closer to the heavier end of the seesaw (the sprung mass end) because we reduce the effective mass at the lighter end (the unsprung mass end). I know you have to think this through but I promise it will be worth the effort...

You just have to increase rear roll stiffness as you decrease the RCH if you want to maintain chassis balance, as Marcus noted some years back. Conversely, if we kept on raising the rear RCH to something like 40", the car wouldn't roll at all in turns, and we could eliminate front and rear sway bars. And life would be wonderful until encountering the first bump. Then, the car's dynamic response would be nothing short of nasty.

As I wrote before, every 3-link/Panhard or Watt's link design I've seen is heavier than the existing 4-link equivalent. That's what prompted my comment about the next-to-impossible-to-package Satchell link configuration*. But if we add some mass to the rear and simultaneously reduce RCH, then the net result might actually be reduced total unsprung mass.
_________________

*You can approximate a Satchell link by using a 3rd link up at top as is being currently proposed, and adding a link to one of the two bottom stock trailing arms in triangulation. Unsprung mass would be nearly identical to the existing 4-link. This would package better than a Satchell link, but it's still far from a panacea. One or both mufflers would still need to find a different home. But the nice thing about this is the considerable RCH benefit in going from the existing 18" to about 7".

Posted By: MAP

Re: Rear 3-link - 04/05/20 08:09 PM

If I could stretch the theory in this conversation just a little more, notice that in the last post I talked about how mass in roll is influenced by RCH and the unsprung and sprung masses, in a comparison with a seesaw. In reality, all bumps at a single axle can be resolved into common-mode and difference-mode inputs seen at the wheels. If the axle rides over a ridge that deflects both wheels identically, then the input is purely common-mode. If the car rides on a flat surface and rolls in a curve, then the input is purely difference-mode. All suspension motion at a single axle can be resolved into a combination of the two modes.

So the very bold thing I'm saying is that the total reflected mass to the wheels, i.e., what we call the unsprung mass, is different between the common mode and the difference mode. It's always lower for the common mode, because purely vertical deflection of the suspension involves no lateral motion of the sprung mass component. The difference mode does create lateral motion of the sprung mass component, unless the RCH is exactly zero. Changing the RCH is exactly analogous to moving the fulcrum on a seesaw: when the RCH is zero, that's the equivalent of placing the fulcrum exactly underneath the end that supports the sprung mass.

One consequence of this complex relationship is that the weight we would measure with, say, a wheel scale under each rear tire, is not the same as the effective weight that's translating dynamically when the car is moving.
Posted By: MC96

Re: Rear 3-link - 04/07/20 01:11 AM

^ Thats the kind of stuff I like reading, makes me think.


https://gbodyforum.com/threads/zr2-s10-8-6-rear-in-a-g-body-build.63106/

As promised, like to the "sandwiched plate" I spoke of.

Couldn't find a link for the bolt pattern of an 8.8 cover, or a 7.5. Havent exhausted my possible sources yet though. If it comes to it I can take a 7.5 I have and Travis' 8.8 into work when life is back to normal and plot it all using the DRO on a bridgeport.
Posted By: MC96

Re: Rear 3-link - 04/07/20 03:38 PM

Correction to the above post, meant to say "link" not "like"


And In response to Hunter. I feel the same way, I've got plenty of my own time to waste, heck sometimes I get to waste it on the clock at work.

The 8.8 rear truss seems hokey to me, never liked it. If it works it works though.

I did happen to find a file for the 8.8 cover. Hunter PM me maybe we can get the ball rolling on a test part. I have a jig for all the pick up points.
Posted By: MC96

Re: Rear 3-link - 04/08/20 03:22 PM

[Linked Image]


On top of getting further along with Travis' brace last night I made a first draft of sorts for an 8.8 4 link.

I do not know if they are offset so I didnt put any in it and who knows if the ears, once bent, end up putting the bushing hole in the same spot but it will be good enough for a test fit.

The tab on the bottom and the hole on the top are to stand off a set of cheap rod ends and a tube to further brace the top ears from twisting.

I think it will nee to be made of 3/8ths steel at minimum, which would be the thickest Ive done on my table, but we'll see.


On unemployment as of Monday, yippee.
Posted By: MC96

Re: Rear 3-link - 04/08/20 08:45 PM

Spent some time with the plasma table today.

I think I have my table dialed in, cut some test brackets for the frame side of Travis' rear.

The picture doesn't show it well but they have a gap of about 1/4 to the frame plate in front of them. That's perfect as I am going to put a backing plate in front of these two plates.

There's also a barely visible hole in that frame plate I want to use to bolt to brace's backing plate.

If you reference the original picture from the first post in the thread it should give a better explanation than my words.

[Linked Image]
[Linked Image]
Posted By: mmc427ss

Re: Rear 3-link - 04/09/20 03:10 AM

My first taste of a plasma cutter was 35 years ago cutting big holes in the roof of a new Ford van to stick a cheery picker in, Ma Bell was the owner.
You would think for as many hacksaw blades I've used up in that time there would be a plasma cutter in house, not. You've taken that to the next level with your setup, can make custom work much quicker, much cleaner, just gotta know how to program it. Cool tool.

My T56 uses a 1/2" thick steel plate to adapt it to old school bells, weighs 17 lbs. Thought i needed it made from alum instead, stopped at S&W to get an idea of what jetting that would entail, the chunk of alum was more than I was hoping to spend. Maybe next time, would have been 10 lbs off the front of the pig, but 20 bucks a pound!

I'm still kicking around the watts or what ever means to lower the RC. I'm certain within the confines back there I can make something fit and get RC down . Adjustable would be good but fixed it you could arrive at a know location to get close to optimum. This will be something for next Winter's project list.
Bob
Posted By: Travis Jones

Re: Rear 3-link - 04/09/20 05:18 AM

Originally Posted by MC96
Spent some time with the plasma table today.

I think I have my table dialed in, cut some test brackets for the frame side of Travis' rear.

The picture doesn't show it well but they have a gap of about 1/4 to the frame plate in front of them. That's perfect as I am going to put a backing plate in front of these two plates.

There's also a barely visible hole in that frame plate I want to use to bolt to brace's backing plate.

If you reference the original picture from the first post in the thread it should give a better explanation than my words.

[Linked Image]
[Linked Image]




looking dang good. Are you thinking of boxing the top? I'm a little worried about the thickness of the outer edges of the holes.
Posted By: MC96

Re: Rear 3-link - 04/09/20 02:05 PM

We could always do that.

I didn’t plan on leaving it as a slot for a final product either. So there will be more margin than ~1/4 at the top and bottom keeping it together.

Once I know generally where the top link locates height wise and have a general length for an upper link I can plot 3-4 holes on an arc
Posted By: MAP

Re: Rear 3-link - 04/10/20 08:27 PM

Hi 96, Going back three posts to the photo of the front UCA mount, I think that roughly - what - 7/8" OD Tube(?) is vulnerable to bending with extreme longitudinal vehicular acceleration. I take it you're going to add a forward extension to bolt-up to the frame's central vertical brace, similar to your first CAD rendition in this thread?
Posted By: MC96

Re: Rear 3-link - 04/10/20 09:59 PM

Yup, thats what I'm in the process of cutting on the table as soon as I get a hold of some 1/4", gotta search my scrap heap.

Planning on fairly thick walled 1" DOM

[Linked Image]

Something like that. Although I know that the hole I am matching to is off center, so I need to account for that.


That and one day Travis will send me the upper link *nudge*
Posted By: MAP

Re: Rear 3-link - 04/11/20 01:49 AM

Looking good!
Posted By: MC96

Re: Rear 3-link - 04/11/20 02:28 AM

[Linked Image]


Now, spare yourself the horror of zooming in on the inner welds, ran out of gas right when I started and said screw it.

I guess that means I get to go to TSC tomorrow.

Our governor has extended our “stay at home” order until the 30th but we might be called back before then. Something about ventilator parts, I don’t see things moving quickly enough at work that they are ready for us to make something new by the 30th anyways.
Posted By: MC96

Re: Rear 3-link - 04/11/20 02:31 AM

Oh and that hole offset was measured as 1/2 to the passenger side, which matches the hump of the rear frame crossmember and actually the drivelines’ offset.
Posted By: SSLance

Re: Rear 3-link - 04/11/20 02:08 PM

I like the direction this is headed...
Posted By: MAP

Re: Rear 3-link - 04/21/20 08:47 PM

Hi 96,

In re-reading this thread, it somewhat resembles a solution in search of a problem. What is the problem statement?

Best,
MAP
Posted By: MC96

Re: Rear 3-link - 04/21/20 09:58 PM

I think in simple terms Travis wants to allow the rear end free-er articulation in tight cornering situations.

I'll have to defer to him on his thought process, I'm just the dummy with the welder (and plas table and rear end jig)
Posted By: MAP

Re: Rear 3-link - 04/21/20 10:15 PM

Hi 96,

You deserve much more credit than that, 96. I don't know what 3-D modeler you're using (Solidworks?) but driving that kind of software is hardly a common skill. Plus, not everyone uses the kind physical tools you use.

"Freer articulation." Ah, the question of the century. I did a mathematical proof 15-ish years ago that in the small-medium signal range, roll doesn't put the factory 4-link in bind. But large-signal is a beastie mathematically and really a job for something like Matlab. Come to think of it, maybe even Solidworks or the like could give you that answer. Here's one approach: without roll, the pivot centers of the rear four CA mounting points define a plane. Put the rear in significant pure roll - say, five degrees. Assume the rear articulates as a perfectly rigid body. Now, do those four points still define a plane? Answer: Yes: no bind. No: bind. One hint to the solution is whether the modeler will solve under this condition. If the solution doesn't converge, look at the error files.

On edit: Naturally, after that, roll must be combined with vertical translation to check for bind.


Maybe it's useful to mention that bind, in roll, is not the same as bushing-induced stiffness in roll, or control-arm twisting in roll. Those artifacts respond collectively as a more-or-less constant roll stiffness. Their contribution is entirely analogous to that of a sway bar.

Best,
MAP
Posted By: SSLance

Re: Rear 3-link - 04/21/20 10:33 PM

The main plus of a 3 link is to be able to change and control the rear roll center height.
Posted By: MAP

Re: Rear 3-link - 04/21/20 11:43 PM

That's quite well known. I was curious from 96's perspective, however.
Posted By: Travis Jones

Re: Rear 3-link - 04/22/20 12:31 PM

Originally Posted by MAP
Hi 96,

In re-reading this thread, it somewhat resembles a solution in search of a problem. What is the problem statement?

Best,
MAP


In short the pinnacle of stock solid rear axle handling performance is the FR500 Ford Mustang. We’re almost replicating that setup in the rear of a G body. This 3 link configuration is confirmed to be better in a racetrack than any other live axle configuration. Math aside, I’ve never seen a triangulated 4 link that doesn’t lift an inside tire on a hairpin. I’ve been in a friends Camaro (former GM ride and and handling engineer) with an S197 rear axle and 3 link and it had grip for days. I’ve yet to see anyone with an A or G body be a contender in autocross on a national level with a 4 link.

S197 axles are cheap, strong, and plentiful. They even have decent factory brakes. Even basic ABS is possible with this rear axle and front S10 ABS spindles.
Posted By: MC96

Re: Rear 3-link - 04/22/20 02:28 PM

Independent roll center and anti squat changes would probably be the selling point for myself
Posted By: SSLance

Re: Rear 3-link - 04/22/20 03:33 PM

Originally Posted by Travis Jones


I’ve never seen a triangulated 4 link that doesn’t lift an inside tire on a hairpin.

I’ve yet to see anyone with an A or G body be a contender in autocross on a national level with a 4 link.



Uh...

That just shows you haven't seen me run yet. laugh
Posted By: MAP

Re: Rear 3-link - 04/22/20 08:27 PM

About that last quote, I'd characterize that as a confounding of factors. The 4-link configuration itself isn't to blame, but rather a combination of rear RCH and rear roll stiffness. Or, we could lump that together as lateral load transfer as a function of time and of roll resulting from transverse acceleration. Reducing the rear RCH helps tame that behavior.

The Satchell link, as I've mentioned a few times, would be a big step in the right direction, because it very much reduces RCH but keeps the low moving mass advantage of a 4-link (which could just as well be reduced to a 3-link with an even further reduction of mass.) But it's TOUGH to package.

About binding: again, an easily confoundable phenomenon. The instantaneous LLT hit at the rear in a turn, owing to the factory's towering RCH (about 18"), creates a twitchiness in steering response that strongly suggests, and is therefore easily confoundable with, binding. When the RCH is reduced but compensated with higher rear roll stiffness, the twitchiness is replaced by a more gradual response that goes in linear proportion to roll, which has a time constant on the order of a few tenths of a second. I remember that Marcus told me about a customer who did this with his '78 Malibu. He benchmarked his best road-course time with the original rear, then used a Watt's link to make a big reduction in RCH. The driver reported that the car felt a lot slower and less responsive, but to his amazement, he found that he had actually reduced his lap time by a few seconds. As Marcus said, the car's steering-response "drama" had disappeared.

That said, of course, binding may really exist. The rear suspension should be tested with all combinations of roll and vertical motion with shocks and springs removed. The OE bushings are cylindrical sleeves which tend to have a disproportionate stiffness to lateral deflections of the control arms, and with OE 4-link design, the CA motion is indeed complex. But the response to such deflections should be stiffness, not friction (which leads to binding.)
Posted By: SSLance

Re: Rear 3-link - 04/22/20 10:40 PM

G Body w/4link making hairpin turns pn course without lifting inside rear tire.

https://youtu.be/6PQeYOOHj7g

https://youtu.be/km6jfcw477s

It CAN be done. wink but a three link will be nice as well.
Posted By: MAP

Re: Rear 3-link - 04/23/20 04:37 AM

Funny how easy it was to spot your rear RCH: very close indeed to 18". Long story short, if you remove all rear roll stiffness, then it would take about 1.8g (top-of-head calculation) to raise the inner wheel. So no question that even with this tall RCH, keeping the tires on the pavement at all times is possible.
Posted By: MAP

Re: Rear 3-link - 04/23/20 09:31 PM

I don't know how to explain that I didn't see Travis' reply until now...

Travis, you may well be right within your range of experience, but the interesting question is why your observation is valid (once again to emphasize, within your range of experience, as is true for everyone here.)

To get right to the point, do the 4-links you observe as not being competitive fail because of their towering RCH, or because of bind? Binding can and should be tested and eliminated from the mix first since it's much easier to evaluate than RCH.

After binding is eliminated, then continue to pursue RCH.

Those two factors are the only inherent (sort-of) negatives that a 4-link has over a 3-link. But don't forget that 3-links can bind as well. Those LCAs see the same complex twisting and lateral deflections as they would in a 4-link. Sometimes staying away from PU bushings can be a very good thing indeed in the rear of these cars: better all Heims or even high-durometer factory bushings that deflect under shear, instead of sliding circumferentially like PU bushings and their ilk.

So once again, I'm not saying you're wrong within your range of experience, but I'm encouraging you to drill deeper to find the root cause (I'm surprised your friend, the GM ride/handling engineer, didn't provide that insight.) I'd argue doing that is worthwhile because it may profoundly impact the design decisions you would make toward pursuing your 3-link.
Posted By: Travis Jones

Re: Rear 3-link - 04/23/20 11:24 PM

Originally Posted by SSLance
G Body w/4link making hairpin turns pn course without lifting inside rear tire.

https://youtu.be/6PQeYOOHj7g

https://youtu.be/km6jfcw477s

It CAN be done. wink but a three link will be nice as well.




I still see times where the inside rear is lifting lance, your locker covers up a lot of this. A true-trac or Torsen will tell you exactly when that is happening.
Posted By: Travis Jones

Re: Rear 3-link - 04/23/20 11:42 PM

Originally Posted by MAP
I don't know how to explain that I didn't see Travis' reply until now...

Travis, you may well be right within your range of experience, but the interesting question is why your observation is valid (once again to emphasize, within your range of experience, as is true for everyone here.)

To get right to the point, do the 4-links you observe as not being competitive fail because of their towering RCH, or because of bind? Binding can and should be tested and eliminated from the mix first since it's much easier to evaluate than RCH.

After binding is eliminated, then continue to pursue RCH.

Those two factors are the only inherent (sort-of) negatives that a 4-link has over a 3-link. But don't forget that 3-links can bind as well. Those LCAs see the same complex twisting and lateral deflections as they would in a 4-link. Sometimes staying away from PU bushings can be a very good thing indeed in the rear of these cars: better all Heims or even high-durometer factory bushings that deflect under shear, instead of sliding circumferentially like PU bushings and their ilk.

So once again, I'm not saying you're wrong within your range of experience, but I'm encouraging you to drill deeper to find the root cause (I'm surprised your friend, the GM ride/handling engineer, didn't provide that insight.) I'd argue doing that is worthwhile because it may profoundly impact the design decisions you would make toward pursuing your 3-link.


I've got roto joints on all the suspension points. the car continues to lift an inside rear tire. there is no bind until its on a bump stop.

To some degree, I'm using what Ford figured out, they could have carried over the triangulated four link package of the SN95 / New Edge mustangs from 04 to the next generation, they opted for a 3 link. Surely there was a reason beyond packaging. For reference the Laguna Seca Boss 302 Mustang is only about a second behind the Camaro SS 1LE with an IRS around VIR.

Triangulated 4 links were designed to be cheap, and ride nice. It is impossible to get a triangulated 4 link to handle the way I want it to, in any vehicle. I've driven a dozen of S197 mustangs, they exit corners EXACTLY how I want my car to. Therefore we're throwing the baby out with the bathwater and copy and pasting that setup on a G-body. (this will still be cheaper than putting a 9 inch into the car as well)
Posted By: MAP

Re: Rear 3-link - 04/24/20 01:03 AM

Hi Travis,

Of course this a heuristic journey(!)

Well, if bind is eliminated, we're only left with RCH. RCH with a 4-link only has two practical possibilities: either at the top (e.g., our A/G-body,) or at the bottom (Satchell link.) About 99.999% of the 4-links out there are at the top, which is very roughly 18" off the ground.

I've said for years, actually decades, that such a towering RCH is wrong in every way possible, and especially when driving over bumpy roads. And even worse, when we drive over bumpy roads with stiff-sidewall tires. As I've said many times, in the 1960s timeframe of the genesis of the frame/suspension that got grafted into our A/G bodies, the factory hid a multitude of suspension evils committed for the sake of reducing cost and weight (in that order,) behind the all-forgiving character of very soft, mushy tires by today's standards.

But moving on, two things you say raise an eyebrow for me:

"There is no bind until it's on a bump stop."
How do you know?

"It is impossible to get a triangulated 4 link to handle the way I want it to, in any vehicle."
If the problem is RCH, then what prevents you from getting a 4-link to handle the way you want, if it is indeed true that it articulates with no bind? Does the matter solely come down to packaging (very understandably)?

OTOH, I can appreciate the economy of copying/pasting a known benchmark solution without wrangling with these important but still somewhat theoretical questions. For the sake of advancing the collective knowledge base, however, I think these long-standing nebulous issues deserve definitive answers.

Best,
MAP
Posted By: Travis Jones

Re: Rear 3-link - 04/24/20 01:25 AM

Originally Posted by MAP
Hi Travis,

Well, if bind is eliminated, we're only left with RCH. RCH with a 4-link only has two practical possibilities: either at the top (e.g., our A/G-body,) or at the bottom (Satchell link.) About 99.999% of the 4-links out there are at the top, which is very roughly 18" off the ground.

I've said for years, actually decades, that such a towering RCH is wrong in every way possible, and especially when driving over bumpy roads. And even worse, when we drive over bumpy roads with stiff-sidewall tires. As I've said many times, in the 1960s timeframe of the genesis of the frame/suspension that got grafted into our A/G bodies, the factory hid a multitude of suspension evils committed for the sake of reducing cost and weight (in that order,) behind the all-forgiving character of very soft, mushy tires by today's standards.

But moving on, two things you say raise an eyebrow for me:

"... there is no bind until it's on a bump stop." How do you know?
"It is impossible to get a triangulated 4 link to handle the way I want it to, in any vehicle." If the problem is RCH, then what prevents you from getting a 4-link to handle the way you want, if it is indeed true that it articulates with no bind? Does the matter solely come down to packaging?

Best,
MAP



I don't understand your insistence that the sachel link is an upgrade (It appears to be an inverse triangulated 4 link and would bind just like a triangulated 4 link) or the concept that a triangulated four link is worth saving over what is KNOWN to be the most effective SRA suspension package? If the satchel link was so good it would have been used by someone in production automobile, if the triangulated 4 link was any good, Ford wouldn't have abandoned it for the S197 or GM would have used it on the 82-02 F-body.

I've already thrown over $1500 away trying to make a 4 link handle. I AM DONE entertaining trying to band-aid it with more parts or like Lance does with a locker.

I'll have less $2k in the whole rear axle and suspension assembly, including links/diff rebuild/axles/shortening the housing etc. and I'll be rewarded with a suspension layout which is actually known to work around a racetrack/autox course.

The proof of the pudding will be in the eating. If it works everything will be really well documented so that others can ditch their 4 links too.

So lets keep the discussion on this thread only to 3 link style rear end suspension because it's the path that we we are following here.
Posted By: AkronAero

Re: Rear 3-link - 04/24/20 02:28 AM

Travis - will you be cutting through the floor and/or will there be other clearance and packaging issues? Your thoughts please. Thanks.
Gordon
Posted By: MAP

Re: Rear 3-link - 04/24/20 04:44 AM

Travis, it's understandable that you're well committed to a single course of action. It's just too bad this couldn't be studied further for the greater good - many others are reading here and trying to come to their own conclusion. And, I'm not trying to insist you do anything at all, just to clarify.

Having said that, this is still as clear as mud.

1. Does a 4-link bind, or doesn't it? I asked you point blank but you didn't answer. Much of this debate centers on this still-unsettled question.
2. Remember, once again, that a 3-link can still bind for the same reasons that a 4-link can bind, although it's less likely to do so because CA motion is less conflicted.
3. The Satchell-link I have in mind is a slight variation on Herb Adams' original description of it. His is basically an inverted version of the A/G body 4-link, except the bottom LCAs remain longer than the UCAs. Mine is a 3-link with a single UCA and one of the two LCAs triangulated to define the roll center. It would behave almost exactly like a 3-link with a Panhard rod, and for its greater packaging ease, just pick the latter, although you would lose the slight weight benefit of the Satchell link. I believe Satchell links never got into the mainstream only because they package terribly, not because they don't work.
4. On a road-race course with flat, smooth pavement, it makes sense that a live axle could rival an IRS. But on real roads with bumps, impossible. The live axle simply has too much of a weight disadvantage. If this weren't the case, then the NVH folks would still have us with live axles.
5. I'm not arguing that the Mustang 3-link isn't the best live axle package out there, but I've yet to hear any compelling argument for why it's the best. And until such an argument is presented, one can't presume that a 4-link can't be made to perform equivalently, empirical data notwithstanding. Sorry.

But zooming back out, in the scope of copying something out there that's known to work, your logic is still quite sound - best of luck to you.
Posted By: Travis Jones

Re: Rear 3-link - 04/24/20 07:52 PM

Originally Posted by AkronAero
Travis - will you be cutting through the floor and/or will there be other clearance and packaging issues? Your thoughts please. Thanks.
Gordon


No there should be no cutting of the floor to get this to work, I think. I might have to raise a small portion of the forward trunk floor with a hammer, but theoretically, nothing should be higher than the ears on the original 7.5/8.5 rear. The only "permanent" changes to the frame will be a weld in Panhard bar support.
Posted By: Travis Jones

Re: Rear 3-link - 04/24/20 08:03 PM

Originally Posted by MAP

4. On a road-race course with flat, smooth pavement, it makes sense that a live axle could rival an IRS. But on real roads with bumps, impossible. The live axle simply has too much of a weight disadvantage. If this weren't the case, then the NVH folks would still have us with live axles.




The NVH guys love solid axles. less to fail and rattle out over the life of the product. also cuts down on a lot of harmonics from from diff and CV joints, etc. The ride and handling guys however hate them. Most of the issues come down to the wheel weights of most modern cars. when you look at an IRS or IFS that has 25+ Kn in the REBOUND direction because wheel mass (22 inch wheels wide sticky tires), cars a literally tearing strut mounts out of the towers. the GM T1xx (2019+ Silverado and Sierra) had a huge issue in development where if you took the truck off a small jump it would rip the lower half of a 3mm thick steel top mount apart, my friend fixed it. 40+ Kn's on strut mount in trucks going from fully loaded to unloaded in a jump scenario

That being said, It wouldn't surprised me to see cheap electric cars with stick axles and integrated drive units on leaf springs in the future. If driving response no longer matters because a computer is doing it for you, turn everything into a 70's Cadillac Fleetwood ride, decoupled and soft. The expensive ones are going to have long travel SLA all around.
Posted By: MAP

Re: Rear 3-link - 04/24/20 09:29 PM

Hi Travis,

The "VH" part of NVH for me is part and parcel with the ride aspect you cite. UV joints cog worse than CV joints, but CV with their short half-axles will undergo much greater angular reflections. The higher mass of the live axle means worse dynamic force variation over bumps, no question.

For a given acceleration, maximum reaction force will go in direct proportion to mass. If we have double the mass with a live axle, then we'll have double the reaction force, other things being equal. So, 25-40 kN (I assume you mean kilo-Newtons, right?) would, other things being equal, roughly double. But live axle forces are usually transmitted to stronger elements of the car's chassis, like the frame, while strut towers, being high-up, tend to (my guess) get lower mass (and therefore strength) budgets so the car's COM doesn't shift too high. Also, live axles tend to get softer, lower-performance tires, so acting as a second-order low-pass filter, peak transmitted forces tend to be lower on this basis. But now put stiff performance tires on that live axle, and transmitted forces come right back up. Btw, we know that IRSs don't need to have strut towers. They can be sprung/shocked like live axles, although high motion ratios tend to be bad for VH in the chassis.

I think the bottom line here for NVH folks is that for a live axle with its much higher mass, the VH spectrum will have a lower (roughly sqrt[2] compared to IRS) breakpoint frequency. Lower is very good for the H part. But vibration will have a larger amplitude: the physics demand it. And that's bad.

So bottom line, whether seen as ride, or the VH part, or at minimum the V part, of NVH, the high mass of the live axle is why they've largely disappeared from modern cars. And as performance enthusiasts, where we care about making sure the normal force between tire and pavement doesn't go too low over bumps and dips, else we lose control in a turn, it matters to us too.

If I had to live with a live axle, the lesson for me would be to use tires with much softer sidewalls than on the front of the car. If the torsional stiffness of the tire (about z, that is,) drops too low, then simply compensate with a wider tire. Soft is good, as well, for the high-RCH 4-link folks, because it dampens (not viscously, however,) the twitchiness of the LLT hit in sudden turns that high RCHs create.

Anyway, again, good luck with your endeavor. I see that the binding issue with the 4-link remains unaddressed, which really lies at the very heart of this conversation for others reading here. I come back to saying that iff we remove all binding from a 4-link, then there's no reason (other than packaging convenience) why a 4-link couldn't be made to perform as well as a 3-link, and perhaps slighter better due to reduced unsprung mass. We just need to get the RCH right, so it's the lower LCAs, not the UCAs, that need to get that job done correctly.
Posted By: SSLance

Re: Rear 3-link - 04/25/20 04:00 PM

Originally Posted by Travis Jones

I still see times where the inside rear is lifting lance, your locker covers up a lot of this. A true-trac or Torsen will tell you exactly when that is happening.


This is where it gets a bit tricky...up towards the pointy end of the stick.

I have my car specifically tuned to "release" the inside rear tire from grip at a specific time. If I did not release the inside rear tire under certain circumstances, the grip from that tire will make the front tires push. I had this happen to my car when I re-did the rear suspension package last fall, even with the massive front grip...the inside rear would stay in the track and make the front push. Most all "at the track" tuning for grip involves adding or subtracting inside rear tire grip.

There are many other factors involved for sure, my locker is a big one in this scenario. Truth of the matter is, say I had a Torsen or Tru-trac, I probably could lessen rear roll resistance, keep the inside rear planted and have better rear lateral grip than I have now. I wouldn't say the locker covers up my inside rear lifting, I'd say I have the inside rear "releasing" because it works best WITH my locker.

I have pictures of my inside rear tire 6-8" up in the air, with literally the same rear suspension I have in the car now...so I'm VERY well versed in how and why that happens. It has very little to do with the rear 4 link.
Posted By: Travis Jones

Re: Rear 3-link - 05/26/20 10:23 PM

Well I dropped all the parts off to Drivetrain Specialists in Warren Michigan today.

Rear end will be narrowed to 63 inches WMS to WMS to accommodate the C5 wheels. Claude, the guy who runs the shop made the hard sell to upgrade to a 9 inch style end, which i initially declined, but having lost a C clip, and subsequently an axle before, I decided for the added safety factor to go for it.

The rear end will get all new bearings, 9 inch ends, an Eaton TruTrac 31 spline diff, 3.15 gear, custom Moser axles and a Moser diff cover.

The last piece of information that is needed is the location for the stock lower control arms measured from the wheel mounting surface to the corner of the LCA mount, so they can weld them up.

Does anyone have this info?
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