Throw Out Bearing?

 

Yep TOB. The fixed guide tube attached at the BH (Bell Housing) itself is a crimped part and rides in the TOB guide. The interfaces are not precision.

 

Pivot bushing? My '88 needed one with <44K miles.


I had a weird vibe on my first '86.5 because of bad motor mounts, which went away when I put a chunk of 3/4" rubber sheet (2 x 10-ish, IIRC), under the oil pan. The pax header would touch the frame under the right conditions.

 

Ken, I was wondering when you would chime in? What is a pivot bushing? Not familiar with that term... If you mean the clutch fork bushing - its been replaced. The shift coupler bushings have also been replaced. I may remove the PKalm clamps to see what effect it has on the condition I've been describing... although, I do think they've amplified a pre-existing condition to where its more noticable. I'm thinking the cause may be TT bearings, but wont know till I get her up in the air (AGAIN) to measure the distance to the front TT bearing... 12" is stock.

The 2"X10" rubber sheet... was it very dense? How did you install or did you just shove it in there? I've seen a few posts with an aftermarket product (a yellow pad) that installs under the oil pan and does the same thing. Not sure what its called? I may look into that or if you would provide me a detailed description of your rubber sheet I'll try to duplicate it...

Thanks!

 

jack up the oil pan all gentle like, cram the rubber between the xmember and the pan, lower her down. we can do that at my place if you want Joel.

 

Jake, Thanks for the offer... Looks like I'll need to schedule some work in Dayton

 

Update: I have some TT bearing measurements and the results of a few "at speed" tests recommended above.

The front TT bearing is 6" from the front edge of the TT. The rear TT bearing is 12" from the rear edge of the TT. From what I've read on here both should be approximately 12" inside the TT. So, these measurements indicate the front TT bearing has migrated forward approximately 6"... CORRCET ?

Afterwards, I took the car down the highway at 80 mph (where the vibration is most noticable). Left it in 5th gear and pushed in the clutch & coasted... vibration deminishes, but still noticable. Got the car back up to 80 mph, put tranny in neutral and coasted with NO deminishment of vibration... As I understand the tests, these results MAY indicate the vibration is originating in the TT or Tranny (since the drive shaft is still turning). CORRECT?

 

Hi Joel,

Best thing to do is take away the other spinning/rolling vibration/noise producers from the equation.

With the car stopped and with the trans in neutral, slowly climb up the revs and see if you can feel any vibrations starting at a certain RPM range. Also listen for that noise. You will be better able to diagnose if it really is the TT.

You can also play with the clutch pedal and see if that changes anything while at the RPM range you notice the vibrations/noises.

If the front bearing unit had migrated back toward the trans then you would have vibrations as you climb in RPMs and load. That it seems to have migrated to the front is a somewhat odd failure mode.

What you are describing doesn't sound exactly like a bad TT. It sounds more like something in the clutch to us.

HTH,

 

Thanks. I'll do that in the a.m. and report back. Its difficult to diagnose this issue. I really appreciate all the help!!

 

Constantine, The front bearing is only 6" from the front edge of the TT. Is this an issue?

Also, I'm helping another 928er install his TT & Tranny in a 89 Automatic. The rear bearing (next to the tranny) on his rebuilt TT is also at the 6" mark. I'd like to let him know if his bearing is not in the proper location.

Thanks again!

 

Hi Joel,

It depends on who did the rebuild and how many bearing units were placed into the 1989 TT. Usually the 1987 and up automatics with the 28mm drive shafts only used two bearing units. We found that in those TTs, the rear most bearing unit was much further in toward the front than 6 inches.

6 inches would be fine if three bearing units were used in the rebuild.

However we do not want to say anything derogatory about another vendor's product. You should ask the vendor about the rebuilt TT if you have any concerns.

Our rebuilds always use three of our Super Bearings, even with the 28mm drive shaft, to better support the drive shaft through it's length.

Good luck with your diagnosis.

 

I agree - not looking to give anyone grief. I just wanted to know if this could be an issue. Sounds like it depends on the rebuilder.

Thanks again!

 

O.K. Car at idle in the driveway in neutral... Sometimes it makes the "chatter" noise and sometimes it doesnt - is it weird that it comes and goes ? Anyway, as I increased the RPM the chatter increased with the RMP - not louder, just faster. No extra vibrations at any RPM that I could tell so that part of the test was inconclusive Hard to tell what happens with the clutch feathered in/out, etc...

I'm thinking the car has TT bearing issues with possibly some clutch issues to boot... The clutch intermediate plate, pressure plate & flywheel had some "minor" hot spots on them when we did the clutch R&R. The plates cleaned up very well & smooth, but the hot spots may still be adding to the problem. There is NO DRAG in neutral, or in gear with the clutch disengaged, car doesnt creep forward, etc, so the intermediate plate adjustment seems to be O.K.

I'm planning on doing a TT bearing replacement and we'll check out the clutch AGAIN while were in there... Might as well since were gonna be "in there" anyway!

Thanks for all the help & suggestions! Any additional suggestions, comments or advice are still welcome!

 

Hi Joel,

It could be bad bearings in the TT, but hard to tell.

We were hoping that feathering the clutch would change the sound which would then point toward the clutch mechanism as the culprit.

The upside is refreshing the TT wouldn't be a bad thing for you to do at this point and a bit easier given it's a 5-speed over an automatic.

Good luck,

 

Yep... Its probably a combination of issues so harder to diagnose... the more you peel the onion ya know! The great part is everything is BETTER with a 5 speed!!!

The 928BuckeyeLandsharks are gonna have a multi-shark TT R&R this summer. Great little club with lots of support, experience, BEER and club tools. I'll be in touch about some super bearing prices. Do you guys give a group discount? Maybe we can get a few more guys to take the TT plunge I'll report back on what I find. Thanks again!