strange alignment and tire worn problem.

rnln · 01-30-2010, 12:09 PM

One of my rear tire always wear more than the other. I thought that wheel has more (-) camber but today I found it has less (-) camber.

Mostly consevative street driving, no race.
Ground is leveled, all 4 corners.
Digital gauge is verified.
Weight used on driver seat is around 160lbs. I am around 190lbs.
I found weight and no weight don't make much different to cambers. Maybe my suspension is too stiff.
Tire worn more on the inside on right rear. A lot more compare to the left rear.
Camber on right rear is -0.8 degree.
Camber on left rear is -1 degree.
Is this odd? More (-) should wear more inside tire edge. Correct? So I and my friend thought it's my toe.

I set up the string to measure my rear toe. I am sure string setup is correct, maybe not very accurate but correct enough, and found that toes are perfect on the rear. I can't tell the degree\s but both sides are equal, very equal.

What else can it be? Shock/strut? Can't be. They must be very stiff, because putting 160lbs on the driver seat doesn't make the car come down that much (less than 1/4" at the left rear fender), and camber doesn't change at all.

What can be be? What makes my right rear tire wear a lot more in the inside? I am giving up and starting working on my Toyota now.

ttweed · ttweed's Garage

Quote:

Originally Posted by rnln

What can be be? What makes my right rear tire wear a lot more in the inside? I am giving up and starting working on my Toyota now.

Have you checked the trailing arm bushing? You measured the static toe, but something may be happening dynamically while driving that you can't see or measure in the garage. The 911 semi-trailing arm suspensions toe IN under bump and toe OUT in droop. If the bushings at the forward pivot of the right trailing arm are shot compared to the left, the thrust and squat from acceleration might be adding excessive toe-in from bushing deflection on that side compared to the other. The wear you describe could certainly be from excessive toe-in.

Just a guess. YMMV. I would be looking for anything that could allow more play in the suspension on that side than the other (springplate fasteners to the chassis have been known to tear out, etc.)

TT

dfink · 01-30-2010, 05:51 PM

Corner balance perhaps. Ride height does not nesessarily indicate a good weight distribution.

rnln · 01-30-2010, 08:02 PM

ok. If corner balance affect tire worn, look like I need to come to the pro.
On the trailing arm bushing, is there a trick to check it beside visual check?
Thanks.

Flieger · Flieger's Garage

I think a difference of .2 degree is not far out of spec. I hope the experts can help but I think you might not be in such a bad situation.

dfink · 01-31-2010, 03:56 AM

Quote:

Originally Posted by rnln

ok. If corner balance affect tire worn, look like I need to come to the pro.
On the trailing arm bushing, is there a trick to check it beside visual check?
Thanks.

You could try the tripod method. Put jack under engine, jack up and then measure the height on the fronts. Could indicate if you are way off. I don't think you will get an accurate setting this way. You can search for exact procedure. If the car has never been corner balanced it wouldn't be a bad idea anyhow. Would be a good time to check bearings, brake pads and bushings.

I see this is an 87. If the bushings for the spring plate and front control arms have never been changed then they need it. Brake lines likely need changed if not already done. I would be checking (probably replacing) all vacuum lines. I would take a serious look at the fuel lines. Perhaps some of this has been done already but on a car of that age I can just about guarantee that every piece of rubber on it has deteriorated.

p911dad · p911dad's Garage

My 84' Carrera has always done the same thing and my mechanic(longtime Porsche guy) says he has seen it before. He said it is possibly related to which wheel does the most power transmission. (it made some sense to me, as there aren't too many other plausible explainations considering you have done just about everything you can to equalize things). A couple of times I had the rears dismounted and swapped once in the rear pair's short life(which seems to be 12,000 max) to get the full life out of both. As I recall it is the right rear that wears first.

rnln · 01-31-2010, 09:57 AM

Thanks dfink.

gmeteer,
That's exactly what I have. The right rear is the one, and only the inner edge. Is right rear the drive/power-tran corner, non-LSD? If that is the case, then the right rear can have less (-) camber, but that might hurt performance does it?

p911dad · p911dad's Garage

MLN, I don't know about the camber setting, but my car is non-LSD. GM

rusnak · 01-31-2010, 11:51 AM

Ron, my gut instinct is to think that maybe the right-side rear is toed in more than the left. But that would make you steer to the right to compensate. Have you recently re-centered the front wheels?

rnln · 11:49 PM

I did years ago, and I don't have to force the streetin wheel when driving. I am not go ing to bet my head on the toe, but I checked with the string method and found the rear toes look fine. They are perfectly equal. Still, I can't tell what the problem is.

Anyone has non-LSD and have perfect rear tires worn? Please let me know if you know your alignment spec.
Thanks.