'02 Mustang rear suspension help

I'm trying to help my father sort the rear suspension of his '02 Mustang GT. It has already had some work done. It currently sits on Kony oranges, Kony red quads, BMR springs 1" lowering(535lb/in front 235lb/in rear), poly bushings, Summit Racing tubular rear control arms(upper and lower), and Steeda spherical bearings. All done back in the spring. At present the factory rear sway bar has been removed due to the tubular arms and he is waiting for more budget for the steeda sway bar for tubular arms. Up front everything is fine. Out back, while greatly improved from the 140k mile stock set up, it feels under dampened, over sprung.

The plan looks to be a softer rear spring with a similar 3/4- 1" drop. What spring rate would play nice with the Kony orange STR.T? His plan is to try a set of Global West GWS40-01 3/4" springs, but I can't find any spring rate info. I tried to find further info on the Kony Str.t, but nothing of use from the kony site.

The poly bushings in the rear control arms may be causing some of the problem. They make it harder for the suspension to articulate, thus adding to the spring rate. One thing you can try is to put back the stock upper control arms (if you have them) and see if it gets better. The design of that suspension requires some compliance for it to work. Same problems haunt the GM A- & G-body cars.

Also, I had an 03 GT with Roush suspension. It used poly in the lower arms but retained the stock uppers. Ride and handling was pretty good.

Yup. Poly took all the articulation out, so its binding and not letting the shocks and springs do their job.

Not just poly bushings, the uppers need to twist, which is why the factory arms are so flimsy in certain ways. I'd swap back to factory uppers with factory bushings and start looking for a Watts link or some other setup. I believe your springs aren't too stiff but rather that the suspension is going further into bind and the springing is now being partially provided by the floor of the car.

The rear end has spherical bearings in the upper rear end mounts, so it hasn't "lost" articulation. It's lost compliance with the poly bushings and the sleeves are probably same length as the bushings, so when you torque the bolt down, you induce bind.

The problem with this set up is that he sourced parts from various suppliers and expected them to work well together. The Fox/SN95/etc. chassis is a not a good design but can be made to work if you don't cause it to bind while controlling it's movement. For performance use most Mustang guys use a torque arm & and a panhard bar and remove the upper arms. No more bind.

There are a number of other ways to "fix" this suspension but the most important one is to buy all of your parts from one supplier, Steeda, Griggs, Max. Motorsports, etc. Don't "mix & match" parts unless you really understand suspensions and how they work.

The rear suspension of the Fox body and SN95 is awful, and the best way to fix it is to get rid of as much as possible. Get a Modular Motorsports torque arm or Steeda 5-link.

In reply to jimbbski:

Yeah, this is how guys start cracking the rear floors on these cars, and blame "too much motor" or whatever instead of "too much bind made worse by parts I selected".

The only real way to make the rear suspension work is to convert to 3-link. If it still feels underdamped, get adjustable Koni's and stiffen the rebound till it feels right.

The design of the Fox Body rear suspension is so bad, SCCA put a special allowance in the rules for Street Prepared class, allowing them to convert to 3-link.

If you don't believe me, check the rear suspension of the S197 Mustangs prior to the newest IRS models. Yep, 3-link.

My Fairmont has Global West lower control arms (spherical rod end front, delrin/aluminum rear), an Evolution Motorsports tri-link system (rod ends on both ends), and a Fays II Watts. It works pretty well.

So, poor design and miss matching parts. I think we can figure something out holistically without just throwing parts at it.

He is retired and the car is his summer DD/toy. No autoX or track time.

In reply to neon4891:

"... without throwing parts at it". What are you hoping to hear?

I'd probably return the car to stock on the rear as well as stock springs on the front until you can do this as a package. The Summit lower arms + Steeda bar might be pretty good. Stock upper arms stay until you do a 3 link or something similar. That's my recommendation.

TAKE OFF THE UCAS AND REINSTALL STOCK ONES.

Seriously, you will break the control arm or the torque box. I have seen it happen. Not hyperbole, not exaggeration.

The stock rear suspension is jokingly referred to as quadrabind for a reason, you need the compliance of the big rubber UCA.

The real ( and easy ) answer is to upgrade to Koni Yellow, but I understand that it can be about $600 if memory serves. I run H&R race (something like 850F? but progressive if memory serves) with Koni Yellow on mine and like it.

Depending on what you want to do with the car (fun street or autocross) you will likely want to do it eventually anyways.

I am not sure on the dampening threshold of the oranges, I went straight from stock to yellows, so I can't speculate on where the sweet spot is for them rate-wise.

In reply to pres589:

Let me rephrase, without blindly throwing random parts at it until it is better.

neon4891 wrote: In reply to pres589: Let me rephrase, without *blindly* throwing *random* parts at it until it is better.

Take the upper arms lose from the rear end and attempt to move them through there travel. While they won't move freely, they should rotate. Same with the lowers. If nothing moves without extreme force, you have the culprit.

And make sure the spherical bearings in the upper mounts aren't "pinched" from being overtorqued. When they are, they bind.

There isn't any need to reinvent the wheel with oe parts or replacing what is on the car still.....

Install Panhard. Remover Upper Driver side Control Arm.

Done.....

Thinkkker wrote: Install Panhard. Remover Upper Driver side Control Arm. Done.....

That's what they call the PM3L right?

Cooper_Tired wrote:

Thinkkker wrote: Install Panhard. Remover Upper Driver side Control Arm. Done.....

That's what they call the PM3L right?

Yup, only way to really be able to use "bushings" like that and not have binding in the stock setup.

In reply to Ranger50:

http://www.miracerros.com/mustang/t_suspension.html#Rear

You can't move just one of the upper control arms independently and think you're seeing how the entire rear suspension works together as a system. What does the opposite upper arm do as the axle does something crazy like move vertically? What's that arm's affect on the axle?

Or just, you know, put the uppers back. And then get a sway bar back under the car.

Thanks for the input. I'm just going to have him read through this and let him make the call.

Ranger50 wrote: The rear end has spherical bearings in the upper rear end mounts, so it hasn't "lost" articulation. It's lost compliance with the poly bushings and the sleeves are probably same length as the bushings, so when you torque the bolt down, you induce bind.

Also, this. When I had some poly bushings (before I wised up), I took the center tubes out and added some length to them with a welder, and filed them round again. That way, I could tighten the bolts to spec without crushing the torque boxes onto the bushings. It helped.

The plan is to try the original spring to see if it feels "over sprung". As far as the original upper control arms, he is not sure if he still has them. I will also suggest checking the tq on the poly bushings.

http://www.maximummotorsports.com/Upper-Control-Arms-C98.aspx

You can get a brand new set there.

The thing is, if you run the bolts loose enough for the poly bushings to work properly, then the bolt is loose enough that it moves back and forth in the chassis or arm, thereby causing the holes to become oblong over time. The best thing to do with the aftermarket bushings is to make sure the inner sleeve is long enough that the body can clamp down onto it like it did with the original inner sleeves. That way, there is room for the bushing to work, but it can't move in an unintended direction.