sportscarclassics

After a clutch job the 928 GT has a vibration problem above 5000 RPM. What is out of balance, pressure plate, clutch? The clutch works fine. All the parts were replaced per GT, pressure plate, bearings.
Thanks

Jim bailey - 928 International

List exactly which parts were changed with all part numbers...

sportscarclassics

Jim,
Thanks for the help. With the clutch in there is no vibration above 5000 RPM. With the car parked and in neutral with the clutch out it will vibrate above 5000 RPM. With the clutch in I think I am illiminating the pressure plate and pilot bearing.

Here are the parts.
Pilot bearing 928 02 111 02
Slave cylinder 928 116 237 22
Ball cup bushing for fork 928 116 145 03
Pressure plate 928 116 004 12
Clutch 928 116 01 3 23
Release bearing 928 116 085 08
Clutch master cylinder 928 423 17 3 06

hupp

The pressure plate rotates with the crank clutch in or out, so I would think you would feel the vibration in both cases if an out-of-balance pressure plate was the issue. With clutch pedal depressed, the clutch pack opens and thus the friction disc and torque tube are stationary with clutch pac rotating with flywheel. With clutch in, car in neutral, the entire drive train is rotating. It may be possible that your vibration is associated with the torque tube.

Garth S

With the clutch engaged, the TT and xmission main shaft are spinning, regardless of gear selection.
If you have a long hill and the correct amount of intestinal fortitude, you can coast at an equivalent speed with the engine off to repeat the tests: lets see ... 5000rpm equivalent in 5th = mph ... on second thought, perhaps there's a safer test to get the driveline up to speed with the engine decoupled.
Out of curiosity, are the motor mounts reasonably fresh?

sportscarclassics

The motor mounts are old and I don't know if they are original. If the motor mounts were bad I think it would have the problem with clutch in or out if I am parked and reving the engine above 5000 RPM. Could it be drive shaft bearings?

Jim bailey - 928 International

BerNard94 may have at least part of the answer... the updated release bearing also needs the updated clutch arm 09 version and the updated guide tube the 16 version as noted on our website(unless your car was updated before). It really can make a difference where you buy your parts ... You may now also have a problem with the central tube bearings since the vibration from mismatched clutch parts may have caused the front central tube bearing to migrate away from the bell housing down toward the middle of the tube.That leaves much of the driveshaft not supported and puts too much load on the pilot bearing and clutch short shaft . I also recall that there were a few Sachs pressure plates some years ago that got distributed which were NOT balanced so check for irregular balance marks (drill marks) on the perimeter of the housing .

sportscarclassics

Jim,
Are you say that I need to replace my clutch arm and guide tube with a version 09? I am assuming that if I rev it up with the clutch depressed and I have no vibration then my pilot bearing and pressure plate are ok?
Thanks

Jim bailey - 928 International

It is most likely that you have the wrong arm and possibly wrong guide tube.

worf928

Listen to Jim B. Your car did not originally come with a release arm lever and guide tube that will mate correctly with the GTS-spec bearing that you parts list indicates was installed. If you have maintenance records and those records do not indicate a previous clutch job then - assuming the records are accurate - you have the wrong parts.

If you paid a shop to do this work I would flat-out demand that they install the correct parts for zero labor cost and that they do it right now before the brand new parts you paid a pretty penny for are trashed.

sportscarclassics

Jim,
Thanks for the help. Yes Jim has the knowledge and greatly respected by most of us in the 928 community. Jim has helped me with parts in the past. I did the clutch myself and it was my first 928 clutch job, no one to blame but myself. Jim may I buy the parts them from you? Do you have them in stock? I am assuming that I can pull the clutch arm and guide tube without removing the pressure plate? Thanks

Jim bailey - 928 International

Carl my next shipment of clutch arms is on order and due here around the 16 th , I have the guide tubes in stock. Replacement will require that you remove the clutch assembly to install the release bearing and arm to the pressure plate.

sportscarclassics

Thanks Jim,
Let me know when you have them and I will cruise by to pick them up. Thanks again for your help. I hate to do the same job twice but I will know next time.