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New pilot bearing for sure. The short-shaft splines look OK from the pic, but how about a close-up of the "nose" that fits the pilot bearing? (cleaned).
I agree with James on the surface, both flywheel and PP look pretty toasted. It looks my S4 clutch after 60K miles, quite burned-- must have been the PO
But if it was slipping at all with your right foot down, then things get very hot, very fast. Clutch surfaces which aren't very flat show large burn marks, but this pattern looks like what I found with our S4.
What are your goals? The right thing to do is surface the flywheel (if there is enough material), new PP (the spring gets tired as well as the surface), new disc, new/rebuilt TO bearing, new call-cup bushing, new pilot. That's a couple of Porsche-bucks but should sort it out for the next 50-80K miles.
lots of good suggestions here , I will add a few more,
I would scrub the splines with parts cleaner and a wire brush,
then use a toothbrush to spread the Porsche Hi temp grease on the splines,
do the shaft and the disc splines.
NOTE before refitting the clutch, take the guide tube and the stub shaft install them,
push the stub shaft into the NEW pilot bearing fully,
then pull it out about 3MM this will center the tip of the stub into the pilot bearing.
Mark the shaft at the back side of the guide tube.
Then slide the clamp to the stub shaft and verify that the cut outs are all lined up and your mark is still set.
NOTE this will make it easy to reset the stub shaft when you install the clutch.
NOTE if your having difficulty removing or installing the clutch,
loosen the bell housing bolts till 3 threads left, remove the trans mount bolts,
and slide the TT/trans assembly rearwards, it will ride on the loosened bolts.
Based on your pictures the clutch parts look to be recent no way they have seen 90K miles.
The flywheel and PP have seen some heat though,
so it is time to swap out the PP and cut the flywheel.
NOTE on the flywheel,
the PP mounting point and the friction disc area should both be cut to have the same relationship with the PP,
OR the clutch may slip,
and infact the flywheel may have already been resurfaced and only the friction area was cut thus leading to a slipping clutch.
The release arm looks OK,
NOTE the new bushing is pressed onto the ball first,
then arm fitted to it.
A dab of DC111 or Porsche hi temp grease works well on the ball.
NOTE if the TOB appears to be smooth then you can grease it.
With a new metal drill, drill a small hole into the bearing shield ,
Take a zerk fitting and a hypodermic needle that has a bigger opening.
(kind of like you might use on a horse)
screw the zerk into the end of the needle base,
then put the grease gun onto the zerk,
then inject the grease into the hole till you see it come out the edge of the seal..
wipe off the opening and put a dab of silicone onto the hole.
You now have serviced the TOB and it should last a long time with fresh grease.
NOTE the usual failure of the TOB is that it runs dry from lack of lubrication,
or is contaminated from water from washing the engine.
NOTE if you swap out the TOB then you must also have the correct release arm to properly fit the TOB .
The latest revision is to use GTS clutch parts.
NOTE even when fitting a new TOB I would still suggest to grease it as it seems the bearings dont get as much grease as they could, thus shortening its service life..
NOTE the TOB spins at engine speed, so it is spinning all the time the engine is running.
Note the manufacturing date on the clutch disc....6/96.
It's been replaced at least once before.
The pressure plate will also have a date stamped into it, which will tell you if someone just stuffed a disc in when the clutch was last done....sometime after 6/96.
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
Here is a close-up of the nose of the short shaft, after cleaning.
I don't think the short shaft nose looks to bad.
I think I'll pull the flywheel and take the clutch parts down to a local machine shop, and see what they have to say and can do.
I have only noticed slipping a few times over 6k miles. I would try to push it and make it slip again and it did not. With poor lubrication, could the clutch disk get hung up on the short shaft and cause some slipping?
Are the concentric rings of wear on the clutch disk normal or does that point to the bad cup bushing or something else?
Great points, I will get a new pilot bearing and pre-install the stub shaft and guide tube as you outline.
I think the TOB feels good.
Do you have a picture of where you drill the small hole?
I do have a needle point for my grease gun, is this small enough?
On cutting the flywheel, I had been talking with my brother and he had mentioned the same thing about the PP mounting area. I do not think the PP has been cut before.
Greg,
Good eye, I didn't notice that. I think I had been told the clutch was original. I have a lot of records, but there is a hole from 1991 to 1999..... I looked all over the Pressure plate and did find a series of number on the fingers, 147 003 F&S 5 89. That was the only thing that looked like a date and looks like May of 1989, so an original PP?
Herman,
No ball cup present, probably has not been there since before I owned the car. It has been on my list, I had just been to busy to check. I had seen the info you posted by looking in you previous posts, thanks. I will look at inspecting the ball stud closer for wear or edges.
you only cut the flywheel, not the PP
you drill in the center of the grease shield on the TOB, with a fresh drill the metal swarf may come out in one long shard, just make a hole no further with the drill.
go slow you only need a hole as big as your hypo needle.
if you mess with the ball you may find its been loctited,
I would see if its tight , if its loose then remove it and clean and red loctite it ,
burnish the ball with red scotchbrite pad and clean,
then a smear of DC111 grease so the bushing will go on.
Greg,
Good eye, I didn't notice that. I think I had been told the clutch was original. I have a lot of records, but there is a hole from 1991 to 1999..... I looked all over the Pressure plate and did find a series of number on the fingers, 147 003 F&S 5 89. That was the only thing that looked like a date and looks like May of 1989, so an original pressure plate?
Ken
Wait... The throw out bearing spins at engine speed, only when the clutch is depressed. Correct..?
Anytime the clutch is released (most of driving) the TOB is disengaged and thus not spinning. Right..?
~
No. The TOB housing is attached to the release arm. The TOB (inner race) is attached to the PP.
It spins all the time.
You can get noises out of it while pressing on the pedal (releasing the clutch) because the forces on it are different when the pedal is pressed and when it is released.
Helpful hint: Listen to Stan (MrMerlin). He knows what he's talking about.
you only cut the flywheel, not the PP
you drill in the center of the grease shield on the TOB, with a fresh drill the metal swarf may come out in one long shard, just make a hole no further with the drill.
go slow you only need a hole as big as your hypo needle.
if you mess with the ball you may find its been loctited,
I would see if its tight , if its loose then remove it and clean and red loctite it ,
burnish the ball with red scotchbrite pad and clean,
then a smear of DC111 grease so the bushing will go on.
Stan, any recommendation on type/brand of grease to pump into the TOB?
Here is a picture of my bearing.
Is this the seal surface that you were talking about? It seems to me that when the clutch pedal is pressed down this is a surface that takes load from the ball-bearing inside the bearing?
If this is the surface to drill into, should the hole be in the center, outer or inner edge?
Or am I not showing the correct thing at all.
I put a mark on the bearing.
The bearing feels a little dry but it spins nicely and does not feel gritty.
Release bearing
I did get my flywheel resurfaced today. It looks much better.
They said they took off about .010 inch of material.
Here is a picture of my bearing.
Is this the seal surface that you were talking about? It seems to me that when the clutch pedal is pressed down this is a surface that takes load from the ball-bearing inside the bearing?
If this is the surface to drill into, should the hole be in the center, outer or inner edge?
Or am I not showing the correct thing at all.
I put a mark on the bearing.
The bearing feels a little dry but it spins nicely and does not feel gritty.
Release bearing
I did get my flywheel resurfaced today. It looks much better.
They said they took off about .010 inch of material.
Thanks,
Ken
Resurfacing the flywheel gives people a false impression.
All of those original black "hot spots" are still there, because the metal has actually changed hardness in those locations. After a few miles of use, all the hot spots will re-appear. The grinding process just smears the harder and softer areas all together so that they look nice and the surface is flat. (Which is why they grind them with a stone....turning one in a lathe (like was done when the flywheel was made) is impossible....even the best carbide tooling just bounces off of the hot spots.)
Regardless of that, what you are trying to accomplish is to replace the clutch pieces as needed to have it hold the power (easy to accomplish, with a new disc) and be smooth (these single disc clutches are very forgiving, when properly lubricated and installed.)
The biggest problem with these clutches occurs when people try to mix early and late T/O arm and T/O bearing pieces.
The rule to remember is that the T/O beaing and the T/O arm must have one "crowned" surface and one flat surface. Both crowned....bad. Both flat....terrible.
02-06-2016, 11:27 PM
