meldog21

I know the possibilities cover a lot, but I'm hoping that someone will have a good idea where to start to save me time figuring this out.

I have a C5 Z06 with Pfadt sways, shocks, bushings, and camber plates, running the Z06 18x10.5 wheels all around with 285 fronts and 305 rears. Running a compromise street/track set up of 0 toe, -1.7 camber, 7 castor front, and -.05 toe, -1 camber rear. The car has about 50,000 total miles. Probably 20,000 miles or less and 10 or so advanced group track days on the current set up.

Here are my two problems:

1. What appears to be fairly loud tire noise, but it comes from only the left rear tire. It doesn't seem to make any difference on which of the 3 kinds of tires I have on the car. Nitto R2s, PS2s, or Kumho 710s.

2. There is a slight change of direction or instability when transitioning on and off throttle. Not crazy left/right, but enough that you can notice the car is not completely stable when applying or lifting throttle.

A cursory look at the suspension did not reveal anything obvious.

For the tire noise I was guessing wheel bearings?

Naturally the instability sounds like an A-arm(s) with bad bushings changing toe, and I haven't disassembled anything to check, but you'd think the poly bushings wouldn't be worn out so soon. So for the instability I'm stumped at where to look first.

So what I'm asking for is opinions on what are the likely cause or causes, and a list of what to check.

Thanks in advance.

Oh, don't feel bad if you point out something super simple that my super simple mind didn't think of. I won't be embarrassed or insulted. Any suggestions would be great.

Dog

sperkins

Noise sounds like a hub bearing.

Handling issue sounds like a toe issue to me, but here are some other things to check:
Loose/bad tie rod ends
Front upper control arm bushings (snap rings)
Loose axle nut
Worn differential

froggy47

Are the wheel bearings original? If yes the likewise for the "tire noise".

Did you currently check the alignment (for changes) or is that what it was set to some time ago?

meldog21

I have not done a recent check of the alignment. Last one was some time ago, but I have hardly used (less than 2k miles) the car in the last 1-2 years because I was doing a grad program at night. So time wise it was a while ago, but mileage not so much.

My hope is that I can solve my issues before I take the car back to the shop for set up/ alignment/ corner weighting.

Dog

redtopz

Also:
Loose lower rear control arm bolts
Worn poly bushings

I would get the rear up off the ground and start by wiggling the wheels side to side and then up/down to see if there's any play. Then remove the wheels and grab the hub and try to push forward and back to see if there is any slop in the control arm connections.

Pfadt Racing

Well it does sound like there is a good chance you've got a damaged wheel bearing. We would suggest replacing the bearing as your first troubleshooting step and then evaluating the car after the repair. Bad wheel bearings can definitely cause a car to do all kinds of funny things handling wise, so take the opportunity to fix the known problems first.

meldog21

One problem solved. Left rear upper arm front bolt was hanging out about 1.5". Luckily the nut is welded into the bracket so all I had to do was re-install the bolt. That should solve the on and off throttle instability.

I ordered 4 wheel bearings/hubs and some new ARP wheel studs. They should arrive in a day or so. I went with the Timkin. Priced in between standard replacements (approx $200) and SKF (approx $1,400).

I'm guessing the loose bolt contributed to the tire noise too since the toe would change based on acceleration, deceleration, or braking.

Dog

froggy47

Glad you found it. Those take a high torque setting, I would suggest you go over all the control arm bolts. They have different torque values. Put a mark so you can see if it loosens again.

I always pull all wheels b4 an event (even autox) and look at my witness marks and 2x a year I put a torque wrench to everything major under the car that could cause a handling/braking issue. Shocks. Brakes.

It doesn't take long. You might be surprised what you find, especially if "other people" work on your car.



I like ck lists myself.

I would not have gone Timkin, on this forum (based on the threads I have read) close to 100% preference is SKF (regular) or SKF (race). You did say you run in the advanced group for DE's?

Just my 2 cent's.