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#1065577 - 03/20/20 02:45 PM Rear 3-link  
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MC96 Offline
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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!


86 SS
400SBC, 4l80e, MSD Atomic injection/trans controller, Tilt glass clip, all tubular arms, corvette brakes, 9" rear
In progress
#1065578 - 03/20/20 03:37 PM Re: Rear 3-link [Re: MC96]  
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SSLance Offline
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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...


Lance
1985 Monte Carlo SS Street Car
#1065580 - 03/20/20 04:10 PM Re: Rear 3-link [Re: MC96]  
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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.


86 SS
400SBC, 4l80e, MSD Atomic injection/trans controller, Tilt glass clip, all tubular arms, corvette brakes, 9" rear
In progress
#1065581 - 03/20/20 05:29 PM Re: Rear 3-link [Re: SSLance]  
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Travis Jones Offline
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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

Last edited by Travis Jones; 03/20/20 05:55 PM.

86 SS 6.0L LQ4, TBSS GEN IV intake, 92mm TB, 30lb injectors, Summit Stage 3 NA Cam, Stainless long tube headers, Stainless 3in exhaust, Microsquirt ECU, FABbot AR5 5-speed, Torsen LSD, QA1 Lvl 3 Suspension Kit, UMI Front & Rear Braces. Check out my build blog on Summit Racing's OnAll Cylinders https://www.onallcylinders.com/author/travis-jones/
#1065582 - 03/20/20 05:45 PM Re: Rear 3-link [Re: MC96]  
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MC96 Offline
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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.


86 SS
400SBC, 4l80e, MSD Atomic injection/trans controller, Tilt glass clip, all tubular arms, corvette brakes, 9" rear
In progress
#1065584 - 03/20/20 05:57 PM Re: Rear 3-link [Re: MC96]  
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Travis Jones Offline
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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.


86 SS 6.0L LQ4, TBSS GEN IV intake, 92mm TB, 30lb injectors, Summit Stage 3 NA Cam, Stainless long tube headers, Stainless 3in exhaust, Microsquirt ECU, FABbot AR5 5-speed, Torsen LSD, QA1 Lvl 3 Suspension Kit, UMI Front & Rear Braces. Check out my build blog on Summit Racing's OnAll Cylinders https://www.onallcylinders.com/author/travis-jones/
#1065627 - 03/22/20 09:19 PM Re: Rear 3-link [Re: MC96]  
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MAP Offline
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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

Last edited by MAP; 03/22/20 09:32 PM.
#1065639 - 03/23/20 02:50 PM Re: Rear 3-link [Re: MC96]  
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MC96 Offline
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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)


Last edited by MC96; 03/23/20 02:50 PM.

86 SS
400SBC, 4l80e, MSD Atomic injection/trans controller, Tilt glass clip, all tubular arms, corvette brakes, 9" rear
In progress
#1065643 - 03/23/20 09:37 PM Re: Rear 3-link [Re: MC96]  
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MAP Offline
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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?

Last edited by MAP; 03/23/20 09:48 PM.
#1065650 - 03/24/20 03:25 AM Re: Rear 3-link [Re: MAP]  
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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.


86 SS 6.0L LQ4, TBSS GEN IV intake, 92mm TB, 30lb injectors, Summit Stage 3 NA Cam, Stainless long tube headers, Stainless 3in exhaust, Microsquirt ECU, FABbot AR5 5-speed, Torsen LSD, QA1 Lvl 3 Suspension Kit, UMI Front & Rear Braces. Check out my build blog on Summit Racing's OnAll Cylinders https://www.onallcylinders.com/author/travis-jones/
#1065651 - 03/24/20 03:46 AM Re: Rear 3-link [Re: MC96]  
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MAP Offline
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Hi Travis, I'm not familiar with that suspension. I come back to my question for 96 as I asked it.

#1065654 - 03/24/20 05:58 AM Re: Rear 3-link [Re: MC96]  
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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

#1065661 - 03/24/20 02:47 PM Re: Rear 3-link [Re: MC96]  
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MC96 Offline
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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.


86 SS
400SBC, 4l80e, MSD Atomic injection/trans controller, Tilt glass clip, all tubular arms, corvette brakes, 9" rear
In progress
#1065662 - 03/24/20 02:59 PM Re: Rear 3-link [Re: MC96]  
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MC96 Offline
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[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

Last edited by MC96; 03/24/20 03:00 PM.

86 SS
400SBC, 4l80e, MSD Atomic injection/trans controller, Tilt glass clip, all tubular arms, corvette brakes, 9" rear
In progress
#1065663 - 03/24/20 03:16 PM Re: Rear 3-link [Re: MC96]  
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#1065721 - Yesterday at 06:24 PM Re: Rear 3-link [Re: MC96]  
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MC96 Offline
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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]


86 SS
400SBC, 4l80e, MSD Atomic injection/trans controller, Tilt glass clip, all tubular arms, corvette brakes, 9" rear
In progress
#1065730 - 10 hours ago Re: Rear 3-link [Re: MC96]  
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MAP Offline
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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.


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