High Speed Vibration
12-09-2005, 08:59 AM
#16
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If your vibration is through the floor/body, and not the steering wheel, I think you are wasting your time, if you look in the front. This clearly sounds like it's coming from the back of the car. If it's purely speed related, it's some of the rotating parts in the rear. So I'd look at half shafts, discs, and wheels. I bet it's one of these three; possibly amplified by some weak transmission mounts or other worn rubber pieces.
Do your wheels turn freely? I once had a car that had vibrations at certain speed - hardly noticeable when it was cold, but getting worse after driving for a while. After a long, long search we found the rear drums were warped. Under certain conditions the wheels would not turn freely all the way around. New drums, no vibration. 928 only has parking brake drums, but if anything on the brakes is warped, the effect could possibly be the same...
Best of luck!
Do your wheels turn freely? I once had a car that had vibrations at certain speed - hardly noticeable when it was cold, but getting worse after driving for a while. After a long, long search we found the rear drums were warped. Under certain conditions the wheels would not turn freely all the way around. New drums, no vibration. 928 only has parking brake drums, but if anything on the brakes is warped, the effect could possibly be the same...
Best of luck!
12-09-2005, 09:50 AM
#17
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Some time ago, I remember a problem someone had with a component in the rear. One of the ends of the connecting shafts( sorry the correct nomenclatere escapes me) was manufactured incorectly, causing a vibration. It was on the 928 OC public list, I think.
12-09-2005, 10:10 AM
#18
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One possible check (sorry if you have already done this and I missed it) would be to CAREFULLY support the car on very steady, high-quality jackstands located on the rear uprights, and run it up to speed. WARNING - Be certain that you do not run it up to speed with just one wheel turning! That wheel will be doing twice speedometer reading, and you can do serious damage!
If the vibration is present, CAREFULLY look under the rear end at half-shafts, etc. Look for any visible wobbling or bouncing.
Remove both rear wheels, making sure that the brake rotors are retained, and repeat.
If the vibration is present, CAREFULLY look under the rear end at half-shafts, etc. Look for any visible wobbling or bouncing.
Remove both rear wheels, making sure that the brake rotors are retained, and repeat.
10-15-2007, 03:46 AM
#20
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Sorry to bring up this old thread, but it seems to lack a conclusion 
After (almost) getting the clutch right on my car, other little annoyances begin to materialize - In particular a vibration at high speeds (as far as I can tell, it peaks between 140 and 160 kmph).
I went through the usual tire/wheel/bearing replacments with no change at all, and started wondering about bushings, springs and so on, then stumpled upon this thread.
Now, I know I need to fix the handbrake because I've adjusted it as far as it will go on both cable and the little adjustment screw, and it only "just" works. Sometimes, it seems like something moves inside the drum causing an annoying, although faint, "clack-clack-clack" sound. The sound goes away if I pull the handbrake while moving (slowly
), but always comes back again after a while...
My question is: Could the handbrake issue and the high-speed vibration be related? For example, could the spring be so "tired" that the centrifugal force of the wheel would allow the handbrake to partly engage at speeds? (Sounds dangerous??)...
(It may be worth noting that even though I obviously have no way to measure this, the vibration does not always appear equally bad - sometimes its just noticable, others, it's really annoying. )
After (almost) getting the clutch right on my car, other little annoyances begin to materialize - In particular a vibration at high speeds (as far as I can tell, it peaks between 140 and 160 kmph).
I went through the usual tire/wheel/bearing replacments with no change at all, and started wondering about bushings, springs and so on, then stumpled upon this thread.
Now, I know I need to fix the handbrake because I've adjusted it as far as it will go on both cable and the little adjustment screw, and it only "just" works. Sometimes, it seems like something moves inside the drum causing an annoying, although faint, "clack-clack-clack" sound. The sound goes away if I pull the handbrake while moving (slowly
), but always comes back again after a while...My question is: Could the handbrake issue and the high-speed vibration be related? For example, could the spring be so "tired" that the centrifugal force of the wheel would allow the handbrake to partly engage at speeds? (Sounds dangerous??)...
(It may be worth noting that even though I obviously have no way to measure this, the vibration does not always appear equally bad - sometimes its just noticable, others, it's really annoying. )
