Car pulling to left on acceleration and right on deceleration, that about covers it.

1992 230 whp, koni, GC, FM front sway bar, stock rear sway bar, Torsen, 205 /50/15 star spec.

Some street some track car. Been built going on 5 years and always runs flawlessly and this issue seems to be getting worse. I have not done much research on the problem other than lifting and shaking wheel and nothing loose and nothing visually loos broken. What could cause this, where do I start to look. I'm sure it could be the 23 year old control arm bushings but rather not tackle the job to find out its not the issue.

If your rolling at 40 and open it up when boost comes on it starts heading left (not violently but gradually) and when you notice it if you let off fast it immediately heads right. Very strange.

Ideas? thanks!

 

tire pressure

 

Tried it. Even tried different tires and wheels. Did seem worse with the borrowed set that was a higher profile but could have been in my head.

 

and the tread is even on both? I had this exact problem when I had a set of wheels and 1 of the 4 had slightly more tread on it, no matter how I switched them up it would do what you're describing.

 

I'll have to check that.
Lets say that is it. Why? Is it messing with the torsen?

 

Is there any chance that either sub-frame is loose?

 

Doubt it? But I'll check. I imagine it would make some noise if it was.

 

Check for a brake dragging. Pads not letting loose.

 

Rear alignment caused this for me once. The shop didn't tighten one of the eccentrics quite enough and it adjusted itself. After that, on and off throttle were two different directions for the rear end.

 

I would think it's either brakes or alignment issues.

Assuming it's the brakes, even if you don't have a temp gun, it sounds like the drag should be substantial enough that you can feel the heat difference side to side using the back of your hand. Also there's the obvious "one side has way more brake dust that the other side" thing.

If it's not obvious like that, it's probably in the alignment. The fact that it got progressively worse might indicate the eccentric bolts slowly shifting on you. /shrug

 

This is starting to sound like a strong contender too

 

See if I can get it on rack in next few days.

 

I would check the rear suspension bushings.
Just sayin

 

Brake drag, or bushings. Those would be the two I'd start with. Then, maybe a binding bearing in the hub?

 

Brake/bearing drag doesnt make sense, neither does alignment, it would pull to the same side no matter what. Now a lose alignment bolt where the alignment was changing with throttle would make sense. Or some busted *** bushing on just one of the rear corners would also make sense. Or mismatched tire diameters in the rear.

 

Am I crazy to think that the diff may have a factor in this?

 

Ok here a good one. Today I put 40psi in all tires to eliminate the sidewall deflection and the car now pulls RIGHT on acc and LEFT on decel. It swapped. I'm so lost. Alignment soon and hope to find something.

 

Wait... I thought THAT was your problem all along, as evidenced by your initial post.

Please check your suspension bushings, starting with the left rear of the car.

 

My bad on reporting problem swap what I said.
*edited*

 

The rear alignment will cause the effect you describe. A different one of your rear tires gains dominance over the other when accelerating versus decelerating. If the rear toe is out of spec the car will not simply take an average of the two angles, but rather make dynamic changes as the loading or unloading of each tire gives it a few more lbs of contact than the other. Amateur drag racers always put helper springs in the right rear corner because the car rotates in that direction under acceleration due to the longitudinal rotation of the engine and driveshaft versus the transfer to the latitudinal positioning of the rear differential. Ever notice how drag race cars with frame flex pick up the left front tire first? If your engine and driveshaft rotated in the opposite direction then the left rear would become loaded and the right rear unloaded similarly. In our cars it is a bit less pronounced because of our independent rear suspensions and low torque engines, but it only takes a slight difference to give one tire more grip than the other if the car is neutrally weight balanced.



Independent rear suspension car rotating similarly: