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#1063953 - 11/01/19 12:36 AM Rear spring options for handling  
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After eating up space on Lance's build thread about improving rear stick in a corner decided it was time for this topic to move to Rolling Chassis.
As with all mods to the 86 SS a lot of time searching for info, parts and opinions is done first before the PAYPAL button is pushed.

20 years ago even before the 86 became a toy the first thing on the list to improve was brakes up front, B spindles was the swap choice back then. Today they are still on the car, have been modded several times to fix their ills. Custom centerlink for bump improvement, Wilwood dual calipers, better rotors and pads, moving the LCA pivots to enable 9 1/2 degrees castor, double adj shocks, all using the 700 lb springs, Delrin bushings and Global UCA parts from two decades ago. The current front suspension is actually very good with the combo of parts there. Moving the lower ball joint 11/16" forward was the key to that. Everything got better, turn in, camber curves, bump steer, feel, and cornering all for the price of a couple nuts and bolts, a few costly tools, some MIG wire and gas. Very happy with the end product up front for what it is, and will stay that way on this car.

The focus of this post will trying to get the rear suspension better so it will play nicely with the front suspension. The two just don't get along well now.

The rear suspension has also been improved several times over the years to improve all aspects of driving, whether street, strip or autox. The 8 1/2" has a Tru-Trac, 4.10s, 30 spline axles, LCA relocation, adj UCA and LCAs, adj sway bar, Viking DA shocks and a host of braces. The rear springs are Global West 1" drop spring installed in 99. Oh, rear brake setup is not bad, alum drums, expensive linings, wheel cyl upgrade and an LBS valve work well.

Knowing tires are a large part of the handling package I'm currently limited to the BFG Comp 2 tires on the street in a 255/50x16/GTA wheels. It's a very good street tire but has it's limits at the autox. Have ran Hoosier A6, 275/45x16 at two autox and know they are superior to the BFG, which also have also been autox. Going to an 18" 200 wear tire is in the near future, but for now going through the motions of trying different things in the rear suspension will happen first.

First on the list is try a different spring in the back to see how it effect the rear loose issue. So looking at all the spring offered for a G, and the 3rd Gen F to see what could be installed and still fit the street and track mode for the car. This will be the first change out back. There are several other changes made to improve loose, 3 link, watts, very expensive shocks, but will start with the easiest and least expensive change first.
Bob

#1063984 - 11/03/19 01:15 AM Re: Rear spring options for handling [Re: mmc427ss]  
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Bob I have a rater here if youre curious of the true rate of any of it.

there is a formula but it only works for "square" springs, no small pigtail ends.


86 SS
400SBC, 4l80e, MSD Atomic injection/trans controller, Tilt glass clip, all tubular arms, corvette brakes, 9" rear
In progress
#1063989 - 11/03/19 04:30 AM Re: Rear spring options for handling [Re: mmc427ss]  
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Mason thanks for the rater offer. For the low rates I'm looking at the bathroom scale will be fine. The spring I think would be good to test on a rater would be the variable rate springs that industry is moving toward. At what spring compression the low rate is done and the higher rate take over would be good to know.

Several good places to get the formula to arrive at rate via measurements and math. Pigtail springs do present a challenge when using those formulas. Tried a few and it's a guesstimate on coil turns. Kinda why I made the homemade spring rate tester.
Bob

#1063990 - 11/03/19 04:45 AM Re: Rear spring options for handling [Re: mmc427ss]  
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The first thing to determine a potential new rear spring is to measure the 20 year old, Global West S69, double pigtail, linear,  3/4" drop spring that was, is, a good match for the car. Ride ht, spring rate, ride quality, handling, overall a good spring. Factory rubber insulators were always installed top and bottom, a little less than 1/2" when both compressed. Hard to gauge compression of the rubber when a double pigtail spring pushes on it.

Measured free length of the S69 is close to 13", with insulators 13 3/8", spring, ID is roughly 5.65", wire size is .535".
Some stuff laying around the shop was used to make a spring rate tester. A press using a bathroom scale, some threaded rod showed the S69 is a 130 lb spring.  Only a 260 scale but 128 then 130 for the second inch, it's a 130 spring. This a key number, along with free length,  when looking for a substitute.

Next with spring removed measure the total distance between the rear's pigtail seat and the upper seat. !4 ", the rear is hanging on the shocks at this point. So at 14" a spring would have zero tension, also would not fall out, another important consideration.  Springs that lower the rear usually become a shorter than that 14" measurement..

With no cushions installed, the springs reinstalled, the ride height dropped 1/2'', expected, Compressed spring length was about 8 3/4". So a 13" free length, 130 rate spring compressed 4 1/4" is:  130 x 4.25" = 553 lbs load. To figure spring load you subtract unsprung weight from the corner weight of that corner. Unsprung weight can vary greatly from car to car and difficult to guess at how many pounds it is. The rear, wheels and tires, brakes, 1/2 the weight of the control arms, shocks, driveshaft, sway bar, all effect  the unsprung number on each side of the car. With rear corner weights of 782 and 786 and a guesstimate of 200 lb per side that's about 580 load per side.

Arriving at a load number between 550 and 575 for the new spring rate is the target.  Now to select springs with higher rate to arrive at that 550 -575 load rate means less compression of that spring. So at 550 load with a 200 lb spring only compresses 2 3/4". If the new spring is the same free length as the old 13" spring the car will sit 1 1/2" higher in the back. The old spring compressed 4 1/4". Installing an inch shorter 12" free length spring will drop the ride height with that same 200 rate 1", but still sit to high in the back.

So once you get a handle on how rates, load rating, ride height, free length all work together you start looking for a spring. That's the next page in the book.
Bob

#1064001 - 11/03/19 07:43 PM Re: Rear spring options for handling [Re: mmc427ss]  
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Let's call this spring shopping. Many years of experience buying, getting info on the phone for odd stuff has it's advantages. Sometimes you can get to the engineers that aren't just sales people. It's helps get the answers you need. And having the Moog spring catalog with it's 6 pages of spring specs, all the other web catalogs at your fingertips helps when you go one on one.

First call was UMI.  Great phone conversation. Ramey was close by, thanks Ramey for the input. Their 1" drop rear spring is very close to my Global spring, 130. It would be a great replacement for me, but I'm looking for more rate. Goal is 160-175. That spring is made by Draco, high quality racing spring.

Next was Ridetech, again very helpful and gave me all the specs on their rear spring. It's a Hypercoil dual rate, 150-250 at 12" free, 2" drop they say. From Ridetech it is the only rear spring choice for a G and also used in an A-body. I think the rate is extremely high for a street car. Would be sweet if someone loaned me a pair to try on. Would hate to spend that money and not be able to take the wife along for a ride around the block.

Next called Hypercoil, again a good salesman/tech. nothing in a double pigtail to fit my needs, all to much free length and rate. Back when a street stock was a G-body on the dirt tracks springs were made for the rear with high rates and tall. Nothing from Hypercoil, AFCO, Landrum, Bluecoil, Draco today in a double pigtail. I was transferred to a Hyperco engineer for more info on the Ridetech spring. He was aware of it, a one off for Ridetech and there are no other similarly built, dual rate, double pigtail, at less less rate available. My hat is off to Ridetech for throwing out there that "extreme" spring. We talked about the 3rd Gen F spring install into a G body. He suggested the 18SNP-12-175 spring as a good alternative. It's 12", 5.5" OD, 175 rate, pigtail on the bottom, but tangential on top, meaning not ground flat but should have a rubber seat for the end of the spring to seat in. Just like the stock front spring sits in the LCA of a G-body.

Eibach sells the Pro Kits for only the F-body. Seems they may have moved on to the new hot rods. But their F-body Pro Kit is interesting, #3901.140. A 1" drop, 5.5" OD, 14.13" free length, and a 107-177 dual rate spring. The 107 rate lets them grow the free length, just not sure how all that would work on a G for ride height.

Detroit Speed, several rear springs listed;
G-body 12", 2" drop, 125 rate, double pigtail
3rd Gen F-body 13", 2" drop, 220 rate, double is shown, would think it's not double pigtail.
64-72 A-body 12.75", 1 - 1 1/4"  drop, 150 rate, double pigtail, may be the choice for a G.

Hotchkis has an interesting rear spring for a G, #1901R 13.5" free length, 1" drop, dual rate at 124-159, with a double pigtail sold for both the G and A body cars.Also a 3rd Gen F spring, #1903R, 14.5" free length, 1" drop 4.350" ID on top, dual rate 100-140 lb.

Lots of other springs choices looked at, nothing at this point sticks out, all have pluses and minuses. A double pigtail, single rate spring presents the problem of balancing free length, rate and load. A dual rate seems to be what some have gone to to get the drop necessary using the low rate and have the higher rate kick in once you have used up the low rate when addition load is on that side. As in going around a corner. Have read dual rate springs are not advisable on a track car, constant rate is more predictable handling. Don't know how true that is these days with a lot of the notable spring manufactures offering dual rate springs.

It getting late, just a note on 3rd gen F rear springs. They are pigtail on the bottom, an open coil on top, tangential, with a 4.350 ID. They are meant to be used with a rubber seat on top, they are not flat ground. Word has it there is no rubber seats available, a search for a pair of new or used shows that. Without the seat the spring would be steel against steel, that being the tip of the spring. The G body upper seat  OD is about 4 1/4" and the F rubber seat would sit very nicely there and allow an F spring install. It's just the  thickness of that seat adding to the free height that is a concern. Looking to buy a set of those rubber seats right now to see how they would work with the F springs available.
Later,
Bob 

#1064011 - 11/03/19 11:37 PM Re: Rear spring options for handling [Re: mmc427ss]  
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15.6103

Take a look at that energy suspension number Bob. You dont want an open coil sitting on something flat it will side load the spring and be a headache.

I would have to do some sluething to figure out which one (flat coil not open) I used on the Afco adjustable cups I had. I still think youre gonna end up with those cups before youre all said n done


86 SS
400SBC, 4l80e, MSD Atomic injection/trans controller, Tilt glass clip, all tubular arms, corvette brakes, 9" rear
In progress
#1064014 - 11/04/19 12:54 AM Re: Rear spring options for handling [Re: mmc427ss]  
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Yes I agree, you need a "seat" for that "open coil" (tangential) F spring. The center hole in the Energy 15.6103 is very large. It may move around on the G's upper formed steel seat area.

Here is what a F rubber seat would look like, same idea, just a smaller hole in the center that would sit and locate in a G nicely. I might have to make a trip to U-pull soon to try and find a good used set.
https://www.camarocentral.com/1982_2002_Rear_Coil_Spring_Upper_Rubber_Insulator_p/sus-151.htm

This is a Winter project and will develop as the snow flies here in the NE.

The Global springs are back in the car with the insulators and the adj sway bar rate has been set at the middle setting to see what the results are. Drove the car 80 miles yesterday but all highway driving and no corners to play on. Will be back out on the local roads getting a feel for that change.
Bob

#1064061 - 11/06/19 08:25 PM Re: Rear spring options for handling [Re: mmc427ss]  
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Hi Bob,

One thing that strikes me is the stiffness of the spring under a normal loaded condition. "Linear springs" are rarely exactly that; instead, stiffness depends on deflection, so you want to measure stiffness under a nominally loaded condition. The divergence from linearity tends to be greatest at the beginning of spring compression, which is exactly where most folk, unfortunately, take their measurement.

A bathroom scale can't help you do this right unless you can put roughly 600lb on each spring as a starting point.

Also, it would help considerably if you would define exactly what you mean by the "...rear loose condition."

Thanks,
MAP

Last edited by MAP; 11/06/19 08:30 PM.
#1064068 - 11/07/19 03:45 AM Re: Rear spring options for handling [Re: MAP]  
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I wonder if you can mount a load cell on the spring? Even with that you would have to calibrate the linear curve min to max.


Do it for yourself not the attention of others.
#1064069 - 11/07/19 06:17 AM Re: Rear spring options for handling [Re: mmc427ss]  
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Thanks for the input MAP. I agree the bathroom scale method isn't the most accurrate but it ball parked the same number Global told me the spring was, 130 and I was able to measure 2" of the spring's 4" total deflection. There are so many dirt track guys around here I'm sure someone has a Longacre spring rate checker that would show full range numbers for me. For what I'm doing currently I'm at the mercy of the supplier word on what they sell. What my bathroom scale told me was the 130 Global spring was 128 for the first inch, 130 for the second, close enough for now. And knowing what the car is doing now at that rate let's see what happens when more rate is thrown into the mix. Maintaining the current ride height is critical. This spring choice has nothing to do with lowering the car as the majority of those who change springs only do it for appearance sake.

As for what is "loose". Mid corner to out in a slalom, same in a tight corner, absolutely no understeer on this car the front end is very good. Chasing the tail around an autox is the norm. Yes tire are a big part of that, along with a high dose of engine torque on throttle. But thinking a simple trail and error spring change will at least show me what a rate change does in the rear. Springs are cheap, easy to swap, but dialing in the ride height and keeping shorter spring from falling out is part of the guessing game.

Ron, a load cell! Way to technical for me. Penske can do that, but he just bought Indy.
Bob

#1064071 - 11/07/19 03:19 PM Re: Rear spring options for handling [Re: mmc427ss]  
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With that soft of a spring rate, the sway bar is most certainly over powering the spring on the inside rear and picking that tire up off the track. Its a battle we fight. I'm still trying to dial mine in to get it as stable with the bar as it was with 600# springs and no bar.

Go stiffer on the spring and unhook the bar and see what it does


Lance
1985 Monte Carlo SS Street Car
#1064072 - 11/07/19 07:58 PM Re: Rear spring options for handling [Re: mmc427ss]  
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Thanks Lance.

To run 3rd/4th Gen F rear springs on a G the top insulator from the F should be used with an F aftermarket rear spring. It's has a tangential spring end on top and doesn't sit properly in the G's upper seat without the insulator. Unable to find a new # 10290379 F insulator anywhere (another discontinued GM part) a trip to the local yard was made today. A 4th Gen Bird was sitting right out front, a fork truck, a ply bar, a bandaid, 10 minutes and 30 bucks and a set of insulators are waiting to be cleaned up. SCORE.

This opens up the possible springs to chose from now to get rate and ride height requirements. The Eibach Pro Kit #3801.140 has a rear spring that is dual rate at 109/177 @14.13" tall. Being an F spring (tangential top) shortening the spring is not a problem, the low rate at 109 would be effected. A possible candidate.

Both Hyperco and Afco make a single rate 175 or 200 for the F at 12" but ride ht may be hard to dial in with either spring and at full droop may be to short to stay in without droop restriction. Good thing about both of those springs is they are inexpensive to try.

One of members here emailed me and has a set of Ridetech rear coils he may part with. The dual rate 150/250 with a 2" drop has me curious but it's 12" free length may be an issue. Would think the 150/250 would be a huge difference from the 130 in the car now.

As stated this is a trial many errors project.
Bob

#1064073 - 11/07/19 09:16 PM Re: Rear spring options for handling [Re: mmc427ss]  
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Hi Folks,

Very interesting points here! Lance, you admitted that your 600#/in springs worked because you allowed the inner side of the axle to decompress the spring completely in hard cornerning, so that roughly 150lb of residual unpsrung weight would still load the inner wheel in that condition. In reality, therefore, you were benefiting from a bimodal sping. So 600#/in, strictly interpreted, doesn't tell the whole story.

Bob, I think the key to the problem is how the rear behaves when lateral load transfer is combined with longitudinal load transfer. We're very familiar with how the car reacts when only one of the two conditions applies, but in combination, predicting behavior can be tricky.

For the purely lateral condition, it's easy to assess whether the car is understeering or oversteering: first, find yourself a nice, flat, big section of asphalt where you can safely turn in something like 250-ft(+) dia circles. Second, hold the steering wheel at a constant angle to create this diameter of turn, and start driving the car very slowly along this circle. Be careful to note the diameter of the circle the car is following. Gradually increase the car's speed with very light throttle, picking-up no more than about 2mph per transit. Continue to note the diameter of the circle traced by the car. Be very careful as you go above 0.7g, because the car may want to spin-out, or the diameter of the circle may want to grow much larger than 250 ft. When you have reached what you deem is the highest speed your nerves, or the car, will tolerate, gently ease-off on the throttle, allow some speed reduction through tire scrub, and then start to apply the brakes lightly.

The result of the test is quite easy to interpret: if the circle diameter grows, you have understeer. If it shrinks, you have oversteer, and you'll most likely end the test with a spin-out.

What I've noticed time and again for myself and everyone else I'm aware of, is that a car that we judge "steers neutrally" usually still has significant understeer.

One of the reasons why the rear's behavior can seem so capricious is because in an A/G body, there isn't a lot of weight on the rear, so the size of each tire's traction circle sees fractionally large modulation as we accelerate the car this way or that. Fundamentally, that's why the rear seems so "touchy." It's even worse with FWD, as I know from my most recent experiences. If we could get a bigger fraction of the car's weight sitting on the rear, handling would be more stable and predictable (can't resist a plug for an EV conversion of our cars, with about 60%, instead of 40%, of the car's total static weight on the rear wheels. I'm amazed at the small thinking of traditional hotrodders - but please, no offense here intended.)

So the problem you have with the rear is that high lateral LT with high longitudinal LT tends to make the rear spin-out in severe oversteer, with the inner tire (mainly) losing part or even all of its traction. The art of drifting depends on this phenomenon.

Your best solution, and it's a severe compromise because once again, there's not much weight on the rear wheels, is to aim for as much understeer as you can tolerate coming from the rear under a purely lateral LT condition. So minimizing understeer as it arises from the front is important. Note however, that accomplishing this doesn't necessarily mean that the front will have low roll stiffness. Playing with camber gain can be a big factor too: Lance, I've mentioned that you've left about 2 deg on the table, probably best gained by increasing negative static camber (not that you'd want to use that for the street, of course.)

Back to springs: we'd probably want the rear to have non-linear stiffness in roll, with stiffness highest in a light-roll condition, but dropping with increasing roll, hence Lance's 600#/in "drooping" springs. In theory, this could be done with sway bars too, but the execution would be cumbersome. Can't say I've ever seen it attempted, actually.

Finally a note about rear anti-squat: for a drag strip, this is easy: more, to a point, is better. But for a road race scenario it cuts both ways: high anti-squat is good for acceleration but bad for braking, so you might as well aim for something close to neutrality.

HTH,
MAP

Last edited by MAP; 11/07/19 10:09 PM.
#1064074 - 11/08/19 12:30 AM Re: Rear spring options for handling [Re: mmc427ss]  
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Bob, try BWBs Street grip springs out, they just might be your ticket.

No matter what you do, it'll be a compromise somewhere, you just have to decide which compromise suits you best.

For me, that seems to be an ever changing target... laugh


Lance
1985 Monte Carlo SS Street Car
#1064078 - 11/08/19 01:19 PM Re: Rear spring options for handling [Re: mmc427ss]  
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Sounds like Bob needs to try some coil overs stacked with a digressive rate.

https://www.hypercoils.com/wp-content/uploads/dual_rate_slides.pdf

You preload the secondary spring, then when the force overcomes the preload you transition from just being on the primary to being on both which lowers your rate.

Kind of the opposite of what maybe a trophey truck would have, light long travel to go over "whoops" and a stiff secondary spring to keep from bottoming out when landing a jump.

Gonna need a spring smasher for that


86 SS
400SBC, 4l80e, MSD Atomic injection/trans controller, Tilt glass clip, all tubular arms, corvette brakes, 9" rear
In progress
#1064080 - 11/08/19 09:13 PM Re: Rear spring options for handling [Re: mmc427ss]  
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Hi MC - Now THAT's clever! Very, very nice. I just wish we didn't need bandaids for a rear that's too light. Best - MAP

Last edited by MAP; 11/08/19 11:14 PM.
#1064081 - 11/09/19 05:56 AM Re: Rear spring options for handling [Re: mmc427ss]  
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That is pretty cool. One of the things that sells me about Hyperco is they are noted for quality, engineering, highly regarded.
If you go back just a decade shock technology available to the little guy was a few companies dabbling in double adj shocks. Today I can pay 2 grands and get a pair of very good shocks, something only the big boys had back then. And of course now that you can put coilovers on just about any car, a dozen companies make or sell kits for everything. So now enter dual spring setups. Cool. Just can't see me throwing the cash out to do that, I've got a 30 year old kitchen that needs to get done first.

Couple notes on the F insulators I sourced the other day. Part number on them is #1019587. The 3rd Gen F #10290379 was superseded by the new number. And of coursed nobody has a new set to sell you, discontinued, out of stock everywhere.
Is it a better part, hard to tell, but looks just like the pics I've seen of the 3rd Gen part. The pair pulled came for a rusty white 4th Gen Bird that was sitting on the ground for a long time. They are a hard rubber with a steel insert for the springs seat which rises up to a 2 1/4" hole in the center. Should be a perfect fit in the G frame while using the G's retainer cup and bolt to locate the insulator, AND to help keep a spring in the car.
The steel inserts in the insulator are very thick steel, maybe 10 gauge, good, because it took numerous applications of navel jelly, muriatic acid and wiring brushing to get the heavily rusted off to bare metal. It appears GM had a thin spray of a rubber coating over the enter steel surface, all black when new. Unfortunately the rust bucket donor car made the insert ugly. Two coats of POR with be done and maybe a lite coating of this neat black spray rubber I have.
One piece of the project done. The ability to do either G or F rear springs now, a big +.

Dual rate coil springs. I get the predictability thing, when do they transition. Still remember 20 years ago being told you don't want dual, or progressive rate springs, use linear only so the change is, linear. Today shopping for G and F springs Ridetech, Hotchkis, Eibach, BMR, MOOG all sell dual rate springs and even the big boys, Hyperco, AFCO, Landrum and more produce dual rate springs. The market is flooded with dual rate springs for everything from a Beamer to a Kia. The question is at what amount of compression does the transition happen. With free length not the same from one company to another and what my installed height is compared to other cars will effect when that low rate becomes the high rate. A big variable when selecting springs and will make it difficult to arrive at ride height, rate, and installed height, and now when does that high rate kick in.
That's what makes the F spring interesting, it can be cut to length to adjust ride height. Cutting length should reduce the number of low rate coils and effect the kicking in of the high rate. More to think about when shopping for the spring.

Going back to the Hyperco phone call a little while ago. Now having a direct phone number to an engineer at Hyperco who may enlighten me on this dual rate thing once I have a handle on what I'm talking about.

MAP every time i go for a ride in the car I'm looking for that nice plot of blacktop, 300'x300', flat, smooth, not 50 years old, no light posts and an owner who say "do whatever you want there". That just doesn't happen here in the rust belt NE. But I keep looking cause i know that's where you can find out what the car is really doing in just about all aspects on a flat surface. But living in NE flat is hard to find, especially on the road I drive. Had the displeasure of driving in southern Fl this past Spring, BORING.
Bob

Interesting day, cold, tired of clean rust off the insulators, decide to jump in the 86 and get a cup of coffee. Once the carb was filled ( Lance), the engine fired a continuous belt squeal, wouldn't stop. Pulled the alt belt, lots of slop on the bearing, inspection shows bearing spun in the front housing. A trip to door of the alt guy at 3:10 showed he closed at 3:00 on Fri. No coffee runs this weekend.

Last edited by mmc427ss; 11/09/19 05:57 AM.
#1064083 - 11/09/19 06:54 AM Re: Rear spring options for handling [Re: mmc427ss]  
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Mason, just found this, a very good read about the setup you linked to.
https://shocktherapyst.com/the-truth-about-dual-rate-springs/
Bob

#1064084 - 11/09/19 09:23 PM Re: Rear spring options for handling [Re: mmc427ss]  
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Hi Bob,

Even here in SW AZ where it never, ever snows, finding 300' x 300' of accessible flat pavement is well nigh impossible. And if you're pushing the car to the very edge, maybe 400' by 400' is more like it so a spinout doesn't cause a rigid-object-kissing moment.

A road-race course would be nice, but the closest ones to me are either in SoCal, or up by Lance's neck of the desert in Phx. Both are about 200 miles away, and so far, I haven't felt sufficiently motivated enough to make the trip. Plus, for me the days of A/G bodies are far in the rearview mirror. Sigh...

About expensive shocks: the inevitable average trajectory of technology is that advances push cost higher and higher. Dr. Bose himself said this at MIT in a "distinguished lecturer" series in 1996. I never forgot it. The cost curve has risen faster than inflation and income for performance cars from the factory, and faster still in the aftermarket for weekend-warrior hotrodders. This, in a nutshell, is why cutting-edge street hotrodding is all but dead today except for the wealthy. I predicted this many years ago and got a hostile "No way!" reaction in this very forum. In 1970 a performance car from Detroit cost maybe $5,000, and maybe another $500 of go-fast goodies would have made the car a 1970 street terror. In 2019 such a car might cost $50,000 and maybe another $20,000 would make the car a 2019 street terror. Inflation over this same period has been about 6.5:1. So note the cost ratios: roughly 10:1 for the base car, and roughly 40:1 for the aftermarket enhancements. How I wish I had been wrong about my assessment then and now!

About how to optimize the point of transition in a bi-linear spring stiffness characteristic: experimentation or extensive computer modeling. In our case, that's experimentation. Don't forget that the stops used in MC's linked pages can theoretically be bracketed by soft-bottoming washers so that the transition point isn't so sharp. Basically, your aim is to get small-to-moderate signal steering neutrality (+/-) to transition to increased understeer at the limit of adhesion. Lance did this with 600lb/in springs with one spring loose at the inner rear wheel in extreme cornering. Folks like Porsche do this with active rear-steering. I predict GM will do the same in a revision to the mid-engine C8 (C9?) design. Again, the price of technological advancement...

On that positive note(!) best of luck to you,
MAP

Last edited by MAP; 11/09/19 09:51 PM.
#1064086 - 11/10/19 12:57 AM Re: Rear spring options for handling [Re: mmc427ss]  
Joined: Jan 2000
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mmc427ss Offline
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mmc427ss  Offline
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That's what I figured, experimenting and looking at the results.

As I was going to the grocery store today I heard the screws in a Challenger accelerating the other way from the traffic light. Cool. But just takes all the fun out of suffering through another project. Open a checkbook and have fun. A good friend has two very nice toys, a 69 401 AMX and a 68 glass front 440 Dart. The AMX is being sold and a 100 Year Dodge Anniversary Challenger R/T has taken it's place. He's tired of working on cars.

Just need to make a phone call to Hyperco next week for some logic and then buy a set of spring to try. Have figured out how to use a shorter F spring so falling out isn't a problem at full droop. The F insulator is substantial and can be made to attach to a short F spring and remain attached to the spring. The center hole in the insulator is substantial, 2 3/8" bore and will slid on a lengthened stock spring cup used for a pigtail spring. A short length of 2 1/4" exhaust pipe should work nicely. As the spring comes off the seat at full droop the longer cup will always keep it centered.
And the lengthened center cup can also be used with a "too short" double pigtail spring, From what I see most of the double pigtail springs at 12" would be free at full droop.

I've always ran rubber insulators top and bottom of both springs to adj ride height and had just the right amount of load at full droop where a moderate amount of hand pressure and they were out. The spring and insulator would always stick to the lower mount and had to be pulled away. Hoping that a new shorter F spring sticks to the bottom rubber insulator and the top can float on the tall cup.

Something else can be done to reduce the droop travel which would aid a shorter spring install. A shorter shock or move the lower shocks attachment point a 1/2" . lower. Have already installed LCA relocation which was a PITA to get right. Adding an inch to the shock mount would't be a big deal.
Having small tiewraps indicators on the shafts of the rear shocks has told me unless I run a higher compression shock setting the tiewrap migrates to the top of the shaft. If I'm aggressive on the back roads the tiewraps tell me the shock should be a little shorter. The front Viking went back for shortening when they were install and found to be to long. Maybe I'll just send the rear shocks back to get shortened and an R&R. Beats laying under the car and welding up shock mount extensions.

Two coats of POR on the insulators today, test fit to see how they mate to the car frame next.
Bob

#1064098 - 11/10/19 02:39 PM Re: Rear spring options for handling [Re: mmc427ss]  
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SSLance Offline
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SSLance  Offline
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Peoria, AZ
We are trying to make a 35 year old luxuary car do sports car things. This costs money if you want it to really work.

I can make my car loose, nuetral or tight by twisting a few knobs on my shocks. I can also make it feel loose, nuetral or tight by changing my driver inputs. Shocks are crucial and great shocks will be faster than average shocks every time. They also make spring rate and ride height changes super easy.

I have sold 5 or 6 sets of coil overs to friends with G bodies who are trying to cure these same ills and they all seem to be happy with their choice. I'll price a set of rears out for you Bob just so you can see it's not as expensive as you might think.


Lance
1985 Monte Carlo SS Street Car
#1064100 - 11/10/19 04:52 PM Re: Rear spring options for handling [Re: mmc427ss]  
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T5montecarlo Offline
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Lederach, PA
Searching the Energy Suspension website, they claim that 3.6108 is the correct rear upper coil spring isolator.

Marc

#1064105 - 11/11/19 04:14 AM Re: Rear spring options for handling [Re: mmc427ss]  
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mmc427ss Offline
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mmc427ss  Offline
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Pottstown, Pa
Marc that may be the correct upper for a G/A pigtail spring. The F spring is a tangential top end, not pigtail or ground. A stock Monte front LCA and spring is tangential, has a seat for it to sit in. The top F insulator is a seat for the F spring.

Here is the F stock insulator all be it not available. From GM they were a really nice well made part, list price back in the day almost 50 bucks a piece,
https://hermesautoparts.com/autopart.php?autopart=1995_Chevy_Camaro_-_Rear_Coil_Spring_Rubber_Mounts_(Pair)

I have several sets of the GM top and bottom insulators for our double pigtail springs, and the top of the front springs. You collect them over time after having things apart a dozen times. Now I have a very nice set of the F top insulators.

Lance by now you should know how old school, anal this old guy can be. Now in my golden years it seems it's getting worse. The old school thing just gets worse because of the challenge, not the cash. Fixing something, or better yet call it improved, just for the satisfaction of doing it and seeing the results good or bad. I get the polishing the turd thing, been doing it for 40 or 50 years on cars. Koni adj shocks were on the car for the first 15 years of fun. Viking DA shocks now, who know someday may go coilover, just need to do a straight up rear spring change just to see what the results are first.

I've got a list with 22 spring choices for the rear, narrowed down to the short list, less than a handful. Will make some calls this weeks to verify some specs and make a choice by weeks end.
Bob

#1064107 - 11/11/19 08:14 PM Re: Rear spring options for handling [Re: mmc427ss]  
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MAP Offline
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MAP  Offline
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Yuma, AZ
Hi Bob and folks,

I'll keep this short because I don't want to pull this thread in a direction that won't help you, Bob. About performance costing money: the handwriting's on the wall. Many of today's ordinary family cars do things sports cars of the 1970s could never do. So adding to factors pushing cost higher, we have the fact that the bar is getting higher every year. In my opinion we've arrived at the point where making an A/G body truly world-class in 2019 terms means taking just the exterior body panels of the car, and draping it over an entirely new and updated central core. That core is likely to cost on the order of $100k(+). Think Mark Stielow and his various Camaros, where he's spending about a quarter of a million dollars (if I'm not mistaken) to update a car that cost a few thousand dollars back in the day. And look at the result: a new Camaro still handles better. High-tech solutions like active MR shocks accomplish a lot. Even the best aftermarket shocks are still passive, after all.

The 1960's origin of our lowly A/G body platform has simply become too cumbersome to improve to modern standards. Nearly everything - correction, everything - needs major surgery. But if your goal is restricted to getting around corners the way Lance's car does, then thankfully it's much easier and cheaper to do (that doesn't mean it isn't hard and expensive in absolute terms, but only in relative terms.) It's the 80/20 rule: that last 20% takes a vastly disproportionate expenditure of time, effort, and cost to address. That last 20% mostly comes from taking a car that accelerates well in every direction (the 80%), and adding good NVH, 2019-standard crashworthiness, and Toyota-like reliability. An OEM engineer might actually think 80/20 should get flipped to 20/80 to get the whole job done, but thankfully we're a more tolerant bunch than the average car owner since we're not afraid to do some welding and to turn some wrenches.

OK, just wanted to get that out of the way. Thanks for listening. Carry on(!)

Best,
MAP

Last edited by MAP; 11/11/19 08:26 PM.
#1064112 - 11/12/19 01:41 AM Re: Rear spring options for handling [Re: mmc427ss]  
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BadSS Offline
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BadSS  Offline
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Pearl, MS, 39208
I'm watching this pretty closely. I tried a couple different springs and not sure if I can get the ride height with springs that won't fall out on the rack or doing a Dukes of Hazard jump. Seriously considering the coil-overs for the ride height, but I'm sure I'd be fine with just springs. So, Bob, I may be copying whatever you end up with. Thanks for posting the info!! KG

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