GlennD

Guys - thanks for the suggestions. Long day in the office yesterday so I did not have a chance to explore.

Dave - good suggestion - let me try both - clutch in and in gear and clutch in and in neutral. See if that makes a difference

Wally - thanks. I am feeling good about the front end of the engine - time to start at the rear of the engine. Your suggestions will be the first place I look. I have a spare clutch (and bearings, etc) so I may just rip and replace anyways. Never done a clutch job on a 928 - time to learn.

Really appreciate the suggestions. I will continue to report back as I test and if I find the actual issue as well (save someone else).

Cheers
Glenn

Mrmerlin

how long has it been since the rear pinch bolt was torqued?
when stopping do you feel a thud just before the car comes to a complete stop? if so its a sliding vibration damper .
Its possible to pin the damper in place with screws

928NOOBIE

When I had the clutch done I was lucky enough to find someone factory trained on the 928 and had a source to dynamically balance the major components and the assembled unit before installation; this was the second installation because the first one did as you describe...vibrations getting worse as rpm got higher..

There are 21 parts to the dual mass clutch (if that's what you have)....it was not cheap...but the clutch has an expected life of between 70 and 140k....anything over 100k on a car like that to me is pretty darn good...

And this is what he told me about the dual mass clutch...."you have to put it in, take it out and put it back in until it "goes in right"...and this is from a guy factory trained when Porsche was manufacturing the 928...

I think it's magic....

GlennD

Thanks for all the suggestions.

I just tightened the front end of the engine down after going through every thing. So feeling confident that is all good

Have the exhaust off and looking at the clutch pack. Not really sure where to start yet as I expect this will take me some time and work keeps calling me away.

There is no noise when stopping so I do not believe the vibration dampener in the torque tube is loose but willing to try anything/everything now. Amazing how a vibration can take away the wonderful experience of driving a GT.

Has anyone taken off the torque tube WITHOUT removing the rear transmission? I would like to keep the backend where it is, move the coupling (torque tube to transmission) into the torque tube and just unbolt the torque tube and drop it out? Is this possible? Could not find anything on this in my search.

Straying now into unfamiliar territory. Thanks for ant advice

Glenn

WallyP

You don't have to drop the torque tube to R&R the clutch, if that is why you are asking...

Black Sea RD

Hi Glenn,

Yes, you can remove the torque tube (TT) without having to drop the rear suspension and transmission. There have been many successful TT removals done this way.

The transmission will have to be pushed back a bit away from the rear of the TT to allow some wiggle room as you drop the TT. Just take your time and don't force anything.

Also, your descriptions of your vibe problem sounds more like a rotating assembly problem, i.e. clutch/flywheel, than a TT problem. But it's a good idea to check out everything just in case WYIT.

Good luck with your search.

GlennD

So, the battle continues and the car continues to win

I have the coupler back on the torque tube, exhaust dropped, heat shield out, I have the fork disconnected at the top, I have all the 9 hex bolts out, I have the intermediate shaft towards the torque tube (touching the torque tube shaft). The clutch pack is loose, it wiggles. BUT IT WILL NOT COME OUT! What am I missing it doing wrong ?


Anyone with advice please. Getting a bit frustrated to be so close yet so far

Thanks
Glenn

GlennD

Car: 10
Me: 1

I got the clutch out (finally). I read from others to watch out as the clutch may suddenly fall out. Ha! I wish.

Anyways, I think I may have found the source of my vibration. I have a sleeve that is cracked. This is the sleeve where the shaft guide goes into.
If you look at PET for the 1990, it is the clutch release bearing, item 2 on illustration 301-00

Both surfaces are cracked.

GlennD

So I have to recant.

I found my spare clutch with all the parts and there is no difference between what was in the car and the new pieces in the box.

Seems like I am still puzzled on the source of the vibration.

The clutch I pulled is still in great shape (about 1/4 max used) and all the other pieces are the same - in excellent shape.

Do I put all the new stuff in or leave what was there and put it all back together?

Damn. And I was hoping for something obvious. Other than learning how to pull the clutch on a GT, no further ahead in finding the source of the vibration.

Any suggestions?

Thanks
Glenn

SeanR

Dang, I was hoping your issue would be fixed with new clutch components. We are digging back in this month also. Last time I noticed that a couple of the bolts that hold the clutch in place were of different lengths, so it's possible that it was a balance issue.

I'll update when we get in there and play around.

GlennD

Sean,
One thing that I noticed in mine is the pilot bearing (at the crank side of the shaft) is not seated all the way in. I have about 1/4 inch poking out.

I am going to pull it and install a new bearing and see what I get.

I also wonder is I should take the clutch and pressure plate to get balanced befor reinstalling. Anything now to see if it helps

Cheers

Mrmerlin

Uh wait , dont remove the pilot bearing just yet..


You want to take the stub shaft and install it see how much forward and backwards play it has with the pinch screws inserted but not torqued.

Reason being someone may have not put the pilot bearing in fully to hide another issue.

So what you want to see is that the stub shaft can be pushed into the bearing then pulled back about 3 MM this should center the tip of the shaft into the center of the bearing.
NOW you will see why your bearing isnt fully in.

NOTE when the bearing is seated flush and your installing the clutch pack you will want to make a mark on the stub shaft to indicate proper reference with the coupler and the fact that you seated the stub forward and then pulled it back about 3 MM then inserted the pinch bolts so do a dry run to get this mark on the stub shaft



You will also want the pinch bolts to line up with the groove of the shaft and the coupler.

NOTE you must also check the rear pinch bolt and verify that the cut out is also lined up before working on the clutch area..

Now with the bearing not installed to be flush with the crank your stub shaft will also have to be moived back further than it normally should.

So with the pilot bearing in its unseated state you WOULD want to find that the pinch bolts dont line up.

NOTE You must check the rear pinch bolt first or the front checks will all be off.
'
NOTE when installing the clutch discs the yellow dots must be opposite or 180 degrees from each other and there is a front and rear disc make sure you have them correctly placed ref the WSM for complete instructions .


Please report what you find.
PS pictures are always welcome

SeanR

Here are some notes on the one I've been trying to diagnose, copied from conversations I've had with the owner.

The vibration seems to start out ~ 2,500 rpm and peak around 4,000 rpm. As you’ve seen, it’s a fairly high pitch vibration that varies linearly with rpm, although past 4,000 rpm it seems to trend back downward. I have yet to find a scenario where the vibration is not present. The scenarios I’ve tested include:

Normal driving accelerating up through the gears, both gently as well as pushing it
Coasting down at speed/in gear (clutch out, engine braking)
Coasting down at speed/in gear (clutch in) and blipping the throttle
Coasting down at speed/out of gear (clutch in or out) and blipping the throttle
Alternating clutch in and out while in gear at speed while rev matching with throttle
Sitting still in gear/clutch in (obviously) and blipping the throttle
Sitting still in neutral/clutch out and blipping the throttle
Sitting still in neutral/clutch in and blipping the throttle*

All of the below have been done by me or the owner over the last year to try and reduce it. As said before, it's always been there and was not of concern until I was right seat driving and noticed it.


Constantine torque tube, Volvo hydraulic motor mounts, new tranny mounts, new guide rod rubber bushing, new injectors, plugs, ignition wires, distributors, rotors, coils, and Hall sensor. It's not an engine running issue. I'm leaning towards a balance issue on the clutch assembly.

GlennD

Sean,

Thanks for the info. I am thinking I will put all new parts in to remove any doubt. Stay tuned

Merlin,
I installed the pinch bolt in the rear torque tube and installed both in the front. You were right, I have about 5mm on the shaft. I may still replace the bearing because I am in there anyways.

I will post pictures in the next couple of days. This is a single disk clutch so I do not have to worry about lining up the two disks.

While I have the car apart (clutch out) anyone else wants any pictures of the bottom areas to check, confirm things? Please let me know, it would be my pleasure. The exhaust is off as is the heat shield and cross member. Both bottom trays are also off as well. Car is up about 6 feet off the ground so pictures should not be a problem.

Cheers
Glenn

Mrmerlin

Hi Glen can you explain what you mean from your last post?

What you want to find is that the pinch bolts DON`T line up with the stub moved back and with the pilot bearing out if its position.

The ideal situation is ,
the bearing is flush with the crank,
the stub is moved about 3mm back from full forward,
and the pinch bolts are all lined up