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My 928 is a 1978, MY 1979 car. I have 5 clutch discs in stock, 1 of them (#5 in the pictures) is new but probably the wrong disc (92811601136 according to various sources, for cars build from MY 80).
The other 4 discs are all "reconditioned" with new friction material: 2 of them are from my old car but the splines of 1 of them don't look good (#3 and #4 in the pictures). To me, these discs look the same)
And there are 2 discs (# 1 and # 2 in the pictures) that also look identical to me, but I don't know the part # of these.
According to the PET, the front disc should be different from the rear disc
Front disc: 92811601124
Rear disc: 92811601127
How can I identify which disc is which?
See pictures.
Can anyone comment on these discs and tell me which is which?
Let me refrase my question,
Although all these discs (1, 2, 3, 4) look the same to me there must be some kind of difference. I am sure #3 and #4 came from my car and should be different (front disc and rear disc have different part numbers). How can I tell which disc is a front disc and which disc is a rear disc?
There were two iterations of both disc 1 and disc 2, that differed in whether there was a gap between the liner (marcel) springs and how the discs were rivets. The WSM has this summary on page 30-14 (below):
For the later iteration of discs, the front disc has a shorter (20mm) hub and the rear disc has a longer (28 mm hub).
The splines in your discs #2 and #3 don't look very happy, not sure those are usable. I would measure #1 and #4, and use whichever is thicker, in front, along with #5 in the rear. Hubs point rearward, and don't forget your high pressure copper grease on the splines. #4 looks happier than #1, from here.
Last edited by Rob Edwards; 10-03-2022 at 02:47 PM.
There were two iterations of both disc 1 and disc 2, that differed in whether there was a gap between the liner (marcel) springs and how the discs were rivets. The WSM has this summary on page 30-14 (below):
For the later iteration of discs, the front disc has a shorter (20mm) hub and the rear disc has a longer (28 mm hub).
The splines in your discs #2 and #3 don't look very happy, not sure those are usable. I would measure #1 and #4, and use whichever is thicker, in front, along with #5 in the rear. Hubs point rearward, and don't forget your high pressure copper grease on the splines. #4 looks happier than #1, from here.
Many thanks, this makes me happy (and the fact that I have so many clutch discs in stock).
The entire dual disc clutch thing is a bit of a mess. Porsche changed things, "*****-nilly" and it is difficult to understand what happened when and what was required when it got changed. Even the factory Workshop manual "ignores' several different iterations.
(I only know all of the details, because I was "there" working on all of the different versions.....trying to make these clutches release and engage properly.)
However, here's some information about what you have....and some thoughts:
It's very doubtful that you will "enjoy" mixing different clutch lining materials.
There's a 100% chance that each material will have different friction characteristics (different "bite" and different coefficient of friction.) One disc will always end up doing the brunt of the work and the wear will always be different between the two discs.
Therefore, this eliminates clutch discs #3 and #4. (#3 has terribly worn splines and is junk.) This appears to be a correct set of early clutch discs, however. Disc #3 appears to not have marcels and disc #4 appears to have marcels. (Better side view would be nice.)
The marcels are the "springs" between the linings of the clutch disc, which help "lift" the intermediate plate and the pressure plate off of the clutch discs. The lack of marcels, on the front disc on these early cars, allowed the front disc to "drag". Porsche changed this front disc to one with marcels (which also required a different intermediate plate, with more travel built into it, although worn early intermediate plates will sometimes work fine.)
Clutch disc #5 is a brand new rear factory disc (latest model) with extended hub. This disc requires a "short shaft" with longer splines and a shorter T/O bearing collar. If you have one of the very early cars with the "different" clutch short shafts and short coupler, you would need to replace the torque tube shaft, the coupler, and the "short shaft". You would also need a front disc to match this disc.
Clutch discs #1 and #2 are and interesting mix. They both appear to have marcels (although it's tough to tell from the angle of the picture.....really need a side view of the discs.)
None of the "early" front clutch disc had marcels, so both of these discs appear to be early vintage rear discs. (Marcels with short hubs.)
Compare the thickness of the linings on the clutch discs (#1and #2) to the new factory disc. Some of the "rebuilt discs" have thicker lining and.....suck.
Clutch discs #1 and #2 are and interesting mix. They both appear to have marcels (although it's tough to tell from the angle of the picture.....really need a side view of the discs.)
None of the "early" front clutch disc had marcels, so both of these discs appear to be early vintage rear discs. (Marcels with short hubs.)
Compare the thickness of the linings on the clutch discs (#1and #2) to the new factory disc. Some of the "rebuilt discs" have thicker lining and.....suck.
Many thanks for your expert opinion. Alweays appreciated.
I made some side pictures with thickness measurements. I hope this adds useful information.
Many thanks for your expert opinion. Alweays appreciated.
I made some side pictures with thickness measurements. I hope this adds useful information.
Wow.
Those discs are...trash, at my shop.
Factory discs, with marcels, measure ~8.1mm.
Anything thicker than that will likely not release properly.
Two of your discs (#1 and #4) have marcels and the discs are 9mm+.
Disc #2 does not have a marcel, but does have the thick lining. Might drag with a early intermediate plate.
Disc #3 is strange. Looks like a non marcel disc, with the rivets not tightened enough. Yet 7.6mm.
Lets start somewhere else.
Can you take a picture of your clutch short shaft, coupler, and T/O arm pivot ball, so I know what generation of pieces you have, in the car?
Can you take a picture of your clutch short shaft, coupler, and T/O arm pivot ball, so I know what generation of pieces you have, in the car?[/QUOTE]
I am very happy you are taking the time to look at my clutch. Here are the pictures you asked for. I hope this all adds up. The whole package without clutch discs. All wear surfaces resurfaced. Intermediate plate thickness = 15 mm Right = old original half shaft Left = used replacement Notice left one shorter splines Right = old original half shaft Left = used replacement Coupler 130 mm long T/O arm
I am very happy you are taking the time to look at my clutch. Here are the pictures you asked for. I hope this all adds up. The whole package without clutch discs. All wear surfaces resurfaced. Intermediate plate thickness = 15 mm Right = old original half shaft Left = used replacement Notice left one shorter splines The left one should be the original, with the shorter splines, The right one is an updated version, made for a rear clutch disc with the longer hub.
No matter, both have badly worn splines and you need to replace with one that looks like the right hand one. Right = old original half shaft Left = used replacement Coupler 130 mm long Made for use with "later" torque tube shaft. The "sticky" area is left over from a Porsche part number tag, which makes this a replacement part....sometime in its history.
Great! Galling on ball is from plastic bushing being gone (at some point in time). If the treaded portion is 8mm, it should work ok. If the threaded portion is 6mm, replace the ball and thread the hole to 8mm. T/O arm
Take a picture of the inside of the fork, where the "ball" goes, so the amount of wear can be determined. By the appearance of the area where the T/O bearing sits, this fork has also been replaced.
Great!
Now I know where your car is, in terms of clutch updates. See notes, in blue, in your text/pictures.
Your best bet is to buy a front (late model) new clutch disc and a better/new clutch short shaft. Still available from the aftermarket suppliers. (At least, we have them....)
Use the new rear disc you have (these are only available new, from Porsche, so that's a good disc to have.)
Take a picture of the inside of the fork, where the "ball" goes, so the amount of wear can be determined. By the appearance of the area where the T/O bearing sits, this fork has also been replaced.
Great!
Now I know where your car is, in terms of clutch updates. See notes, in blue, in your text/pictures.
Your best bet is to buy a front (late model) new clutch disc and a better/new clutch short shaft. Still available from the aftermarket suppliers. (At least, we have them....)
Use the new rear disc you have (these are only available new, from Porsche, so that's a good disc to have.)
OK, some good news, some bad news. But at least it is clear to me what to do. Here is the picture of the fork. I posted this picture before because the cup seems to slide in easily. I understand I have to press it on the ball and then press the arom over it.Then it will grip. Seems logical. My original question was what to do with the crush ring because it doesn't seem to fit anywhere but it is in the drawing as a snap ring and it was in the same bag from Porsche. I understand now that it is for another year of car.
I will check around for the intermediate shaft. But getting one from the USA to the Netherlands is horendously expensive. But I'll check your website anyhow,
OK, some good news, some bad news. But at least it is clear to me what to do. Here is the picture of the fork. I posted this picture before because the cup seems to slide in easily. I understand I have to press it on the ball and then press the arom over it.Then it will grip. Seems logical. My original question was what to do with the crush ring because it doesn't seem to fit anywhere but it is in the drawing as a snap ring and it was in the same bag from Porsche. I understand now that it is for another year of car.
I will check around for the intermediate shaft. But getting one from the USA to the Netherlands is horendously expensive. But I'll check your website anyhow,
Not much on my website.
We are terrified of creating more work...
Walked around, yesterday, and there are still 35 928's here, most waiting for TLC. (With a few that are almost ready to "go home".)
Three weeks ago, I had Mary call anyone with an appointment, from then to January and move them into the New Year.
These cars arrive for a post purchase inspection or "Can you get it running" and leave 100 hours of labor, later.
We do make a clutch short shaft from 300M, which corrects all of the "issues" with the factory shaft and is just about 1/2 the price.
And I do have several of the clutch disc you need, in stock.
10-02-2022, 09:12 AM
help identify clutch discs
