Fronkenstein

So I was under the OG (I prefer Old Girl) today hunting down noise and adjusting the clutch disc spacing.

while doing the adjustment I noticed that the discs are very loose. I estimate it at 0.5mm of backlash.This explains the chatter I was hearing.

If this is bad, which I expect it is, what are the odds that it's the discs versus the input shaft or both.

Here is a video:


Any clues, help, suggestions would be greatly appreciated.

Fronkenstein

GlenL

Should not be that loose.

I suggest dropping the clutch and taking a look. Could be a worn splines on the intermediate shaft on on the discs.

christiandk

Loose? Well the clutch is disengaged which will make it loose. How about the coupler? Seated correctly?

Since you have the housing off it wont hurt to drop it and take a look at the components. Watch your head

The Deputy

That looks extremely excessive to me. And I would think that would make a heck of a racket while disengaged.

Brian.

Dave928S

That's a lot more than minor wear, and once it gets to that stage the wear accelerates.

The clutch disc hubs tend to wear a little less than the input shaft, so my guess is that you'll find the input shaft has fairly significant spline wear, with a pronounced step between the two hub wear areas. The spline wear also tends to make the hubs not slide well on the shaft, which affects clutch release and engagement.

You need to pull the clutch out to take a look.

GlenL

It could be a problem with the coupler as well. Consider pulling that, too and especially if the splines are OK.

SeanR

Looks like it's time for some disks and an intermediate shaft.

GregBBRD

Many who work on these clutches fail to lubricate (or lubricate with the incorrect product) the clutch shaft, disc hubs, and other spots that need lubrication.

Buy a tube of genuine Porsche high pressure grease and use it here, and in a multitude of other places.

I make new clutch shafts from 300M material for roughly 1/2 the price of a new shaft from Porsche ($395.00 versus $600+). Higher quality material, cheaper!

Fronkenstein

This clutch had been out and dismantled and the short shaft didn't appear to have significant wear and the discs looked ok. But but it never occurred to me to test lateral play while it was out or while it was over my head while aligning the shaft and with the pilot bearing.

I have a near new original Porsche short shaft on its way as well as two new discs.

Yes it is very noisy. At one point I could swear I heard what sounded like a solid slipping. Now I know why.

Greg, are your replacement shafts hard chromed or some other durable coating?

Has anyone tried swain coating any of the clutch or transmission components?

Fronkenstein

GregBBRD

300M with the proper heat treating is one of the toughest splined shafts that can be made, with current technology. Good enough for things like jet engine shafts, off-road race truck axles, etc.

No coating used and I doubt that any of those spray on coatings would survive for very long in the clutch application.

I never thought about having one DLC treated and trying that. While that may help, over many 100s of thousands of miles, the cost would probably stop most 928 owners in their tracks. DLC, itself, is really expensive and because the surface has to be very highly polished to accept the coating, the shaft would have to be engineered for the material removed in the polishing process. (Since the top of the splines would loose more dimension than the troughs during the polishing process.) A DLC shaft would cost several thousands of dollars each, in the tiny quantities needed for the 928 world.

While I love building state of the art pieces....I think 300M is about as far as needed, for this application.

Fronkenstein

Thanks Greg. If this shaft turns out to be out of spec I will send you a request for one.

Fronkenstein