Need Help from Chassis Dynamics Experts

ohecht · 10-21-2002, 09:34 AM

Well,

I am hoping someone very familiar with chassis dynamics can help me zero in on a wheel-related vibration:

I am still chasing down the vibration in my 82 SC after a hard day's of Driver's Ed. There is more information in an earlier post:
previous post

I had the wheels and tires "rotated" (switched to the other wheels) and balanced and there was no improvement. The vibration stayed present only when turning right, even in very mild turns (i.e. staying in one lane but moving slightly side to side)

The vibration is definitely in the wheels, etc., as disconnecting the drivetrain has no effect.

Front tires are worn, but rebalancing and swapping did not affect anything, so I am hesitant to replace the tires first (although I need to fairly soon). Front rotors were turned <5k ago, but they are not in perfect shape. It does not sound like a bearing howl or grind.

My question to the experts is: Which side/corner of the car should I focus on first using the information that the vibration is present in any right turn whatsoever (and magnified when coasting or trailing throttle) and not there at all when turning left at all? Which wheels have forces on them at these times that would magnify a rotor, wheel balance, etc. issue?

I am worried this is something I could chase and throw parts at forever if I don't narrow it down early.

Thanks in advance,

Olivier

atlporsche · 10-21-2002, 10:14 AM

wheel bearing, outside, left wheel.

You seem to have eliminated everything else...

if it only happens when turning right, on or off throttle. Do you feel it as a chassis shake or does the steering wheel move?? how violently???

sjd

masraum · 10-21-2002, 11:04 AM

My thought would be wheel/tire, but if you rotated and balanced and still have the same problem and it didn't change sides then it would seem to rule wheel/tire out. My second thought would be bearing related. When turning right the left front will take the majority of the load, and if coasting or trailing throttle the natural weight shift will be to the front, so the front left will be carrying even more weight. From there if the bearing isn't the problem then I would check balljoints, tie rods, etc....

I'd probably just replace both front left bearings unless you are on a really tight budget, they'll be cheap insurance. Maybe mic the shaft while you are there.

ohecht · 10-21-2002, 12:55 PM

I feel the vibration more through the steering wheel than through the chassis, but it does feel like it is coming directly from the wheels at times. The CV joints and axles seem fine, but I am not sure how to check the rear bearings and what the spec is for the half shafts moving side to side.

I appreciate the tips. I will focus on the left front, but probably do all the bearings and the bushings as well. The grease that came out of the left side when I repacked the bearings (it appeared OK) was very runny, as if it had exceeded its temperature rating. I have had my eye on that rotor as well, so it may have been adding excess heat during the track time.

Olivier

masraum · 10-21-2002, 01:05 PM

If you suspect heat and brake issues then I would check the front left rubber brake hose. It is common that when they get old they can cause the brake to drag. Also check the caliper for sticking.

ohecht · 10-21-2002, 02:11 PM

The lines are stainless steel, but I will check the caliper again. I rebuilt it shortly after getting the car 2 years ago, when it would stick very badly. I would probably want to upgrade the brakes if it is sticking again.

Thanks,

Olivier

dean · 10-21-2002, 03:28 PM

Can you borrow a friends set of wheels and tire to eliminate yours as the problem. I think bad wheel bearing make noise more than vibration felt in the wheel. It could also be a rotor that lost a balance weight.

ohecht · 10-21-2002, 06:28 PM

I have thought about that, but I do not know anyone locally with a similar car.