Whining Noise: flywheel or pressure plate?

Seth Stevenson · 10:22 PM

Hey, folks. I'm hoping for wiser minds than my own to chip in with a noise that has me flummoxed. I'm a bit of a novice when it comes to working on and diagnosing cars, although 2 years of owning and working on a Porsche has been quite a satisfying education.

I drive an 86 951/944 turbo with a manual limited slip differential. About 3 months ago, I started getting a weird rubbing/whining noise at higher RPMs. The noise is:
1. Not detectable in 1st or 2nd gear. It tends to appear only rarely in 3rd gear, and regularly in 4th and 5th gears.
2. Present typically between 2000 and 3200 rpm.
3. More prevalent at higher temps.
4. Seems louder inside the cabin than outside, and seems to be coming from either the "rear" of the engine bay, where it meets the cabin, or alternatively the front right of the car, near the power steering pump. (I'm half deaf, so these are tentative diagnoses based on friends and family.)
5. Independent of turning.
6. Tends to be worst when the engine is under load, when the accelerator is depressed.
7. It is usually "cured" or terminated by depressing the clutch. However, if the car is in neutral and the engine is revved, then the noise is sometimes reproducible.
8. It seems to be getting worse.

I have recently replaced all wheel bearings, belts, and vacuum hoses. I have replaced the transmission/differential oil. None of these has helped.

The fact that it is not changed by steering direction seems to rule out bearing and steering pump issues, and the continued presence of the noise when the clutch pedal is depressed or the transmission is in neutral seem to rule out the clutch or transmission.

I'm wondering if it could be the flywheel itself or the pressure plate, but I'm out of my depth in terms of definitively diagnosing the problem.

Any suggestions are greatly appreciated. Thanks!

944 Ecology · 07-19-2011, 01:37 PM

Sounds like it might be the Throwout Bearing (which is attached to the Pressure Plate.)

krystar · 07-19-2011, 02:02 PM

seconded on the TOB.

if u depress the clutch pedal, the clutch fork pulls back on the TOB so it'd eliminate any "free play" that'd result in whining noise.

the noise frequency should be proportional to engine RPM.

Guest765 · 07-19-2011, 02:15 PM

Quote:

Originally Posted by krystar

seconded on the TOB.

if u depress the clutch pedal, the clutch fork pulls back on the TOB so it'd eliminate any "free play" that'd result in whining noise.

the noise frequency should be proportional to engine RPM.

this could also be your synchros, as you mentioned it only happens in the higher gears which seems to be the exact opposite of my throwout bearing noise.

don't rule that out.

Seth Stevenson · 07-20-2011, 11:22 AM

Thanks so much for the input so far. Correct me if I'm wrong:

If it is the throwout bearing, then the noise should be dependent on if the clutch is depressed. If the clutch is depressed, then the bearing will be withdrawn from the flywheel, disengaging the clutch/pressure plate from the flywheel as well.

If it is a bad wheel bearing, the noise should not be reproducible while the clutch is depressed, yes?

I tested this out earlier, based on your input, and the rub/whine does occur if I rev the engine while depressing the clutch. It is not as loud, but it is present. Does that mean that it isn't the throwout bearing?

The car shifts smoothly, with no grinding, by the way.

So, the issue must be somewhere "upstream" of the clutch, I'd guess. What are the likely culprits?

If it were the synchros, wouldn't there be issues changing gears, and wouldn't the noise be further "back" in the car?

Thanks again.

Guest765 · 07-20-2011, 11:50 AM

Honestly the clutch is about two feet from you in the cabin and the throwout bearing is always going to make some noise. Depending on how loud it is it might be normal bearing wear. The only way you're going to figure this one out for sure is going to be by disassembling the clutch at this point. Does it make the noise at idle in neutral with the clutch out and then going away when you depress the clutch? You need not be moving to hear throwout bearing noise.

Seth Stevenson · 07-20-2011, 12:09 PM

Alas. A full clutch disassembly is exactly what I'm hoping to avoid...it noise is intemittent at idle rpms, and only occurs after it has started at higher gears and rpms, but it is sometimes present at idle with the clutch depressed.

Is that possible if it is the throwout bearing? Or wouldn't the presence of the noise with the clutch depressed rule that out?

kmakovac · kmakovac's Garage

if you depress accelerator pedal in gears and you heard like a szoow-szoow-szoow soudn and the sound go away if you depresed the clutch pedel then i will give the chance to the torque tube bearings....

there are 4 bearings that have the engine revs and after 25 years they are not new for sure

i have this problem and change clutch,trans oil,grease the joints but without results
when i change torque tube bearing the car feels like a new one!!!
the bearing are a little tricky to change but is possible and maybe is a great deal if you do a clutch job.

Guest765 · 07-21-2011, 06:24 PM

it really could be the torque tube bearings. open the inspection port on the transmission and with the car off have someone hold down the clutch and reach in and rotate the shaft. if it has any rough feeling at all or more than the tiniest bit of noise when you spin it - it's torque tube bearings.