G-body rear suspension... [Archive]

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mongoose

09-04-2008, 11:18 PM

I'm picking up a new frame soon to start on my frame up build with my cutty. I have the front pretty much sorted, but the back i'm still undecieded...

at present i'm throwing around a couple ideas.. a, keep the stock arms use a watts link and hope for the best, b, change up the stock four link to something like a art morrison set up and maybe throw in a watts just for fun, or c) switch over to a 3 bar set up and watts link.

I don't really car about cutting stuff up... I'm just trying to get the most outta the stock frame... well, demensionally at least. and being i've read all this crap about lowering g bodies and how it's bad.. but i want it to be loowwwwwwwwwwww and still not have any problems... if I wanted a high car i woulda bought a truck. =)

any input? any other ideas on other setups?

Marcus SC&C

09-05-2008, 10:53 AM

Are you planning on using the stock frame rails? Mark SC&C

mongoose

09-05-2008, 12:10 PM

I would like to for body mounts n such....

but if it will net me a lot i wouldn't mind swapping them with something different.

redss86

09-07-2008, 08:50 PM

mongoose

09-07-2008, 11:43 PM

Mark has explained on other posts that the watts link will improve RC among others thing even with the the stock set up...

though... my car is rather low.... like 25 ish inches at the wheel well... and my rear end is so messed up it's not even funny...

but... I think i'm going with the 3 link/coil overs and watts... with a torsion bar.

GBodyGMachine

09-08-2008, 07:25 AM

If I had the money and time I would love to run a 3-link with a watts. Nice thing about starting over is you can modify the control arm mounting points so your suspension geometry is not all wacked. If you use the stock 4-link you cand go that low before you loose you geometry.
Jeff

Marcus SC&C

09-08-2008, 09:33 AM

A 3 link with watts would be my top choice. We built one about 7 years ago (with a phb,we`re upgrading it to a watts now) that`s a real hoot to drive. If you`re interested in talking about doing one give me a call. We`re still trying to design a 3 link conversion package as an easy do it yourself kit.

Joe, on paper (or computer) you`re right. The triangulated upper arms should locate the rear axle laterally. But in this case,in practice they do a pretty lousy job of it. Bushings or bearings with less loss to control lateral axle movement tend to bind the suspension vertically and/or in articulation making it a catch 22. It`s all a very fine compromise. Most aftermarket arms don`t adequately address it at all and can make some issues worse. The idea with the watts is to allow compliance in the UCAs using rubber bushings in at least one end (usually the axle side) then let the watts do what it does best,locate the rear axle laterally with extreme precision and dominate and define the roll center. In this case we can use it to relocate it to a somewhat better location as well. I`m the first to admit that it`s not a kinematically perfect solution but in practice it`s startlingly effective and eliminates many of the compromises normally associated with the OE suspension format. Mark SC&C

liquidh8

03-19-2009, 10:25 AM

Have you figured out if you are running a 3 link yet?

Mark, any luck with the 3 link retrofit kit?

Been thinking the same thing for my g-body, 3 link and your watts.

79MALIBU

08-02-2009, 03:52 PM

This has been the year of much autocross for me. I have leaned a lot this year from Mark at SCandC. He convinced me over the winter to try the watts link. The Watts is by far best suspension upgrade I have ever done for the rear.

On the street, on street tires, the watts is a bolt-in set it and forget it. At the auto-cross, it's great tool for controlling over/under steer.

Now about running a low ride height. I suggest flex-joints everywhere. The G-body doesn't like to be lowered. Don't forget to check the bump stop for the pinion yoke, I run a Ford 9 that does not even come close to hitting. I am running about a 25" ride height.

I have been tuning the rear suspension all summer. The trouble begins with binding. (I would like to say here that Marks watts link doesn't bind any at slightly higher ride heights) Binding is easy for me to detect. When I exit a hard turn at high speed (autocross speed 60mph tops) and pick up a rear tire, the Tru-track makes tons of noises when i get on the gas, and the car doen't accelerate as well.

I believe the final solution for me may lie in a 3-link system, and perhaps longer trailing arms. So in a round-about way I am in the same boat.

So who makes a 3-link for g-bodies?
I have access to a machine shop full of tools and career fabricators-if any is interersted in prototypeing? I could share data in Solidworks or CAD . . .. ;)

I know a co-op would take some time, how-ever I plan to try a 3-link system, even if by my own design within 2 weeks.

6spdmalibu

08-02-2009, 07:19 PM

a67

08-03-2009, 02:23 PM

So who makes a 3-link for g-bodies?
I have access to a machine shop full of tools and career fabricators-if any is interersted in prototypeing? I could share data in Solidworks or CAD . . .. ;)

I know a co-op would take some time, how-ever I plan to try a 3-link system, even if by my own design within 2 weeks.

Didn't the Buick GNX run a torque arm? It used a mount that bolted on between the diff cover and diff. Then ran a torque arm to ? Not sure where actually.

I thought I had some pictures of the set up but it doesn't appear so. I don't know if the torque arm replaced the upper arms or not. The uppers really are not required with the TA. Ah, maybe for side to side control. Otherwise a panhard or watts is required.

And I don't believe either was included on the GNX.

Bob

6spdmalibu

08-03-2009, 04:45 PM

Yes the GNX did run a torque arm with a panhard bar.
There used to be a kit available but no longer!
Here is a link with some info:https://secure.mysuperpageshosting.com/kirbanperformance.com/gnx.htm

Jerry

liquidh8

08-04-2009, 03:37 AM

I would love to do a 3 link conversion, or a torque arm set-up. Looking around though, I think there would be trans tunnel mods needed to fit a torque arm in a g-body. For me, I have a century wagon with a LC-2 turbo 6, so the y-pipe would not crossover the torque arm easily. (thinking camaro style, long). The GNX's TA was shorter by looking in the pics, and more for strait line then twisties. Maybe a 3 link would be better to retrofit. The mustangs run them with the 8.8's, and they fit. I dunno if it's the optimal set-up though. Since one would have to compomise the upper arm length to keep the rear seat in place?

Norm Peterson

08-04-2009, 06:54 AM

Didn't the Buick GNX run a torque arm? It used a mount that bolted on between the diff cover and diff. Then ran a torque arm to ? Not sure where actually.

I thought I had some pictures of the set up but it doesn't appear so. I don't know if the torque arm replaced the upper arms or not. The uppers really are not required with the TA. Ah, maybe for side to side control. Otherwise a panhard or watts is required.

And I don't believe either was included on the GNX.

Bob
The GNX (and Kirban's copy) used what's more properly called a traction arm, sort of like a single centrally located ladder bar. It's important to keep the distinction between this and a true torque arm (such as is found under the 3rd & 4th Gen F-body cars) in mind since both the chassis side attachment and the location of the IC differ between a traction arm and a true torque arm. The location of the chassis side pivot for a traction arm is particularly important, otherwise it will bind up against the LCAs as the suspension moves in two wheel bump/rebound (or at least tries to move).

The GNX and Kirban's copy both did away with the "regular" G-body's upper arms and also installed a PHB (now required for lateral axle location).

If a relatively short upper 3rd link doesn't bother you, the existing 4-link upper mounting points could be used to attach some sort of brackets and adapters to that would pick up the ends of a straight fore/aft 3rd link. FWIW, the single upper on the S197 Mustang is only a little over 8.5" pin to pin (compare to the G-body uppers as projected into side view, at ~7.75") while the lowers are about 18.5" (pretty close to the ~18" G-body LCA side view projected length). I'm sure that you could get a 3rd link longer than 7.75" into the available space without a whole lot of effort.

The Mustang is a pretty good target to aim for (or crib from) here, as that car is of very similar weight, height, and wheelbase to the G-body, and is only a little less nose-heavy (about 54% vs 56% or so). Track-Pack models are hitting mid 0.9x lateral g and crowding 70 mph in R&T's 100' slalom spacing.

Norm

Samckitt

08-04-2009, 07:17 AM

GNX suspension:

https://static1.pt-content.com/images/noimg.gif

GNX Crossmember:
https://static1.pt-content.com/images/pt/2009/08/gnxsuspensioncrossmember-1.jpg

Torque arm from crossmember to rear aluminum cover:
https://static1.pt-content.com/images/pt/2009/08/gnxsuspensionladderbar-1.jpg

a67

08-04-2009, 11:18 AM

Good info on the GNX rear suspension setup (thanks 6spdmalibu). Probably the reason I couldn't quite recall the GNX set up is that I don't have pictures of that setup. My mind was working on a visual from another car.

The GN here has the beginnings of a torque arm system. There is a plate between the diff & cover that has a TA mount on the drivers side (left hand side). However, it has the 4-link still in place and no TA.

I wonder what the builder had in mind for this set up.

The 3rd gen f-body TA is rather long compared to the traction link on the GNX. Goes from the front of the diff to the tail of the tranny. Although the '89 TTA's received a cross-member with the torque arm mount on it.

Norm, with what you posted I agree that a 3-link on a g-body would be straight forward. That and an off the shelf Watts would be a good way to go.

Having a 3rd gen f-body I do not like the feel of the panhard bar on curves. The vehicle isn't the same through a right hand vs a left hand turn. Worst yet is that the jacking is on right hand curves, which nearly all on ramps are.

Bob

liquidh8

08-04-2009, 04:12 PM

Norm, this is exactly what I was tossing around for my junk. I have a ford 9 going in. Plan on fabbing a bolt in bracket "for testing" and use a third link from a S197, or fab/ebay a boxed piece with johny joints. Use SC&C's watts, and try it out. If it sux, I could change it pretty easy. Since its a wagon with the turbo 6, with glass hood, bumper, aluminum rad, and the like, I hope to improve the f/r weight dist. too.

This is my winter project, so I am following all you guys too and when I get started I'll start a new thread to keep all posted. But for now, I am just following and participating in the "brainstorming", lol.

liquidh8

08-04-2009, 04:13 PM

a67

X2

79MALIBU

08-04-2009, 05:42 PM

Trying to come up with a better alternative to the stock suspension as well. Any and all information that you'll provide will be appreciated. My project won't start till late fall, so I'll be curious to see your decisions on your setup.
Meanwhile, are you going to keep the rear seat use able? Or will the car be a track car only? What amount of anti squat are you shooting for? If its a dual purpose car, what amount of roll under steer is desirable? How long will the side view swing arm be to combat brake hop?

Jerry

I plan to keep the rear seat. I am not looking for much anti-squat. I have Anti-squat brackets I could add if i needed them for the strip. But I am running about 400hp at the fly and use Kumho Ecsta V710, so if I can keep them on the ground they will hook at the autocross. Autocoss is the priority, but I do keep the car set-up as a competitive 1/4 mile bracket car. The rest will be determined later. I hope to hit the drawing board pretty hard this weekend.

GregInAtl

08-09-2009, 10:48 AM

a few of you guys say your wheel wells are at 25" (rear?!) Are you completely bound up currently too much for street driving, and this is just an auto-x upgrade, or are you now undrivable w/o breakage?
I am trying to get 25" rear wheel wells on a 26.5" tire set up and it just wont happen. How did you do this and post a pic or two.
I am 26 1/2 Right rear 26 1/8 left rear...my whole left side is 3/8 lower F&R??!
car- 86GN

Norm Peterson

08-10-2009, 06:03 AM

I wonder how closely the various years/models of G-body rear wheel well heights match up?

Reason being that based on my '79 Malibu, putting a 26.5" tall tire on it and then lowering it down to 25" would give a mind-numbing amount of axle roll steer (think 20% !!!). And there's already way too much of that as it is (around 8%).

Norm

novaderrik

08-10-2009, 07:18 AM

why do people measure their ride height based on where the wheelwell is sitting? each body off the line is going to be a little different, and if a quarter panel has ever been replaced, then who knows where it will end up.
i'd think it would be better to measure to the bottom of the frame at the point right in front of the front wheel and behind the front wheels. this would give you a nice solid point of reference that would be more repeatable from car to car.

Norm Peterson

08-10-2009, 08:12 AM

Agreed that a frame refernce is the better way.

But it's just too much easier to lay a yardstick up against the side of the car and look at it. Maybe for most folks it's only an appearance issue, so a little bit of laziness can trump decimal-point accuracy as far as what they're looking for is concerned?

Norm

malibu43

08-10-2009, 02:22 PM

Hi guys am JORGE from CHILE.
I got a 80 malibu coupe,and i race this car as road course.
Ihave lots of questions so if you can help me with advices,and maybe i donne everithing wrong.
The car has a 350 engine,4 speed,4:11 gears non posi,my car its lowered about 6 inches from the lowest side of frame to the ground,all solid bushings,i swap the rear coil springs for softer ones(from a nissan 4 cylinder),all rear arms are boxed(iv´read somewhere only the lower has to be boxed ,never the upper) .
But i make faster turns the rear end tries to pass me,.
QUESTIONS. remember its for road course, not straight line.
how much low has to be the ride height? how much travel has to be achieve in the fron and rear end(from wher do i have to take the measurements)if i took all the weight from the rear end what has to be the spring rate?.
Guys i really need help in this matter ,please let me konw everything you know about this g bodys,and if you have some pics will be great.
From the last country of the world regars.
JORGE

79MALIBU

08-10-2009, 05:40 PM

I just measured my ride height 24.5" left 24.25 right. The car is currently loaded with a heavy set of auto-x rims. So it is sitting a little lower than its normal street height, but not much. My tires are 25.1" tall.

My theory on different measurements per side is about the springs and weight in the car. Our rear springs are fairly light. Enough so that a full tank of full will take to car out of balance, and compress the left side slightly more than the right. In my case right now I have a heavy toolbox on the passenger with little gas in the tank (I drive this car up to 100miles to the Auto-x tracks), causing the right to be slightly lower.

My lower control arms actually point downhill toward the front of the car right now. Its not Ideal, which is why I am building adding a top link and plan to put anti-squat brackets on the lower control arms to bring the up to level.

As far as bound up goes, I do need more free movement for the autocross, but street driveing is fine. I am running flex joints in the ears of the to mounts and in place of bushings on the Lower control arms.

As far as an update for my top-link system goes, I have selected the joints and tierod style bar that will be the link. The concept for the brakects is work-out. Actual design will begin when the parts are in my hands. Currently the plan will involve some welding, and perhaps some heating and reshaping of the frame attachment point.

6spdmalibu

08-13-2009, 10:22 PM

Besides the bind issues of the G body rear suspension. How would lowering the rear roll center height improve handling? From what I understand, it would transfer more weight. And how would that improve slalom times?

Norm Peterson

08-14-2009, 03:23 AM

By itself, lowering the rear RC will cause less load to be transferred at the rear. That's assuming that you lower that RC without adding a PHB, WL, or other "extra" means of laterally locating the axle.

If you lower the rear RC and re-balance the springs and sta-bars (generally, a little more rear stiffness), the amount of understeer would be expected to remain more consistent, rather than getting progressively heavier as the lateral acceleration builds.

Specifically in slaloms, the amount of rear axle roll steer also becomes important. In the triangulated/converging 4-link arrangement, roll center height and roll steer are two results from the same geometric construction.

Norm

6spdmalibu

08-15-2009, 03:40 AM

So then how should one proceed in getting a better geometry out of the rear suspension within the confines of a stock frame?

Norm Peterson

08-15-2009, 04:54 AM

You can 'crutch' the geometry issues by making the car stiff enough in roll (stiffer springs and larger bars) so that the absolute amounts of roll steer don't amount to much. Downsides include a hard ride and poor behavior over bumpy roads.

Or you can scrap much of the OE and put something else in there. 3-links, torque arms, and truckarms are the street-friendly choices, ladder bars and non-converging 4-links are the dragstrip geometry-revision counterparts. LCA relocating brackets are kind of a baby step in this direction (they'll reduce roll steer in addition to increasing anti-squat, and the increase in RC height is negligible).

Additional links, such as a PHB or the Watts link available through SC&C don't really fall into either of the above categories but will provide benefit under at least some conditions.

As far as hard cornering and the converging/triangulated 4-link suspension (and replacements for it) is concerned there's a lot of generally useful information on the forums that cater to the Fox/SN95 Mustangs. The C4L for those cars differs from the G-body only in the plan view angle between the uppers and the fact that the rear springs are seated on the LCAs instead of on top of the axle tubes.

Norm