I've got a 99 GT that I have run locally in several auto crosses, the car has Eibach lowering springs, the taller ball joints for the new roll center and a bumpsteer kit, The car also has convertible subframe connectors on it from auto-xing in NASA awhile back. I recently installed a MaxMotorsports panhard bar and here's the problem...
When I crank on the bar to center the rear, (rearend moves to the left, the chassis bracket is located on the right) the bar mount acts like a fulcrum and raises the right rear. Once the rear is centerred, the right rear is at least 1.5 inches higher in the air than the left rear. I placed a 3/4 rubber "donut" under the left spring to help compensate, but ni deal, the right rear is still at least 1inch higher. I also tried the heim style upper control arm mounts tor free up the rearend, but same thing, it didn't help. I guess the next step is a set of weight jacker lower control arms but I hate throwing more money at something that is no longer my primary competition car. BTW, because I'm sure you will ask, I didn't take any measurements prior to the install. I seemed pretty strightforward, just crank the rear over to where it needs to be. Have any of you guys experienced this phenomenon before?
Thanks for your help.

 

Mustang guys may not respond here, but maybe we can talk anyway.

I would set the panhard bar level to stop it from lifting/lowering the suspension.

Raising/lowering the panhard bar is a stock car trick to get more or less side bite in a turn.

There should be no tension or compression on the panhard bar
when sitting track ready at track ride height.

I would solve the problem of one side higher, not by raising the opposite side, but by lowering the side that is too high.
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"crank the rear over to where it needs to be"...........
Some questions: Why does the rear need to be relocated side to side?
What located the rear when the panhard bar was not there?

Since panhard bars are a locating device for multi-link suspensions, can you shoot us a drawing or pic of what the rear suspension design
looks like?

There are some designs where the rear end pumpkin/gears are offset to one side, and if we can see your suspension design, maybe we can tell if the rear actually "needs" to be centered.-Bob

 

Maximum Motorsports Panhard Bar install with pics. Multiple threads inside. - Corral Forums

write up on installing and other links to threads on the panhard bar to get an understanding. A panhard bar helps keep the wheels centered in but they also keep the rear from moving side to side during cornering.

As far as the OP problem, couldnt tell you havent installed a bar yet. Are you doing it with the chassis loaded or the car up in the air? I would try checking on cornercarvers or just Maximum-Motorsports, they are supposed to be great with tech help over the phone