'78 clutch replacement - need some advice please
05-30-2019, 10:46 PM
#16
Rennlist Member
Thread Starter
Greg - first thanks for your continued replies in trying to sort this problem because I know you must be very busy. It has been a few weeks since this last happened so my memory is not totally clear but I don't recall that the gears, including reverse, would grind while I was driving the car the couple of miles back home and backing it into the garage. The clutch was operable but from your choices I would say more of a rattle or rubbing noise. It had some vibration in the pedal also. Up until this the clutch was perfectly smooth. I was driving down the highway, pushing the revs a bit between shifts, pulled off the ramp and then when I moved off again I felt something catch a bit and then every time I would operate the clutch it would disengage but not smoothly nor quietly.
I was very careful to look everything over as I was taking it out. The H stops were all perfectly adjusted, all the pressure plate bolts were tight, the intermediate shaft seemed to be in the correct position, the clutch fork was on the bushing. The only irregular thing I could see was the thrust washer jammed up against the slip ring. Even so, how much would that affect the I function of the TOB? I guess if the thrust washer is not sitting in place and parallel to the TOB that the TOB could tilt some when the clutch is operated and therefore make noise. But the centering tube should help prevent any tilting of the TOB.
I also mentioned earlier that, as I was searching for answers and checking things over, that the rear pinch bolt at the transmission was not fully torqued. I had not touched that bolt during the two previous installations. I was actually able to move the main shaft back and forth slightly until I secured the pinch bolt. Is it possible that the main torque tube shaft was moving longitudinally enough to affect the TOB? This would allow the intermediate shaft to move also, correct?
So again thanks for your time and continued response.
I was very careful to look everything over as I was taking it out. The H stops were all perfectly adjusted, all the pressure plate bolts were tight, the intermediate shaft seemed to be in the correct position, the clutch fork was on the bushing. The only irregular thing I could see was the thrust washer jammed up against the slip ring. Even so, how much would that affect the I function of the TOB? I guess if the thrust washer is not sitting in place and parallel to the TOB that the TOB could tilt some when the clutch is operated and therefore make noise. But the centering tube should help prevent any tilting of the TOB.
I also mentioned earlier that, as I was searching for answers and checking things over, that the rear pinch bolt at the transmission was not fully torqued. I had not touched that bolt during the two previous installations. I was actually able to move the main shaft back and forth slightly until I secured the pinch bolt. Is it possible that the main torque tube shaft was moving longitudinally enough to affect the TOB? This would allow the intermediate shaft to move also, correct?
So again thanks for your time and continued response.
05-30-2019, 10:58 PM
#17
Rennlist Member
Thread Starter
Thanks GJB928 - I reviewed your thread and your guide tube showed pretty obvious signs of metal to metal contact, much worse than mine. Have you had your torque tube rebuilt? Mine is noisy, clanky and could be causing some excess vibration through the clutch pack. Could be the source of your noise.
05-30-2019, 11:27 PM
#18
It could be, but it sure feels like it's in the clutch. I'm going to take it apart again to inspect. The whole thing with the different length tube has me worried. I'm going to watch your thread with great interest.
05-30-2019, 11:51 PM
#19
Former Sponsor
Purely from a technical standpoint, worth discussing, for general knowledge.....
The original early forward clutch disc had no Marcels. The rear discs all had Marcels. (These are the "flat" springs between the two clutch disc surfaces, which compress when the pressure plate pushes on the discs.) The Marcels are what make clutches smooth, when they engage. The "original" intermediate plates had .9mm to 1.0..of "potential movement" between the "H" stops....which was enough to lift the intermediate plate free from the front clutch disc (which did not expand when the pressure was removed.)
When Porsche superceeded the front clutch disc to the current style (with Marcels), they also superceeded the intermediate plate to the current version, which has a "potential movement" of 1.3mm to 1.4mm between the two "H" stops. This "increase" in the movement distance was changed, because the clutch disc "grew" when the pressure was removed from it (the Marcels expanded) and the .9mm to 1.0mm distance was found to be inadequate, which caused the front disc to "drag" and wore out the synchros very quickly. (Also wore the front disc more than the rear disc, since it was "dragging".)
So....there is definite "potential" for the front clutch disc to "drag", when the front disc is changed to one with Marcels, if the original intermediate plate is used. I've fought this problem dozens of times over the years....and finally gave up....I always use the "later" intermediate plate when the front clutch disc is changed to one with Marcels.
The "thicker" clutch discs that Roger supplies makes this problem more complex. When the clutch is bolted together, the actual internal pressure plate in the clutch cover, is forced towards the rear of the car. There are 3 "T" shaped pieces that keep the actual internal pressure plate centered. These "T" pieces go through the aluminum part of the clutch cover and move back and forth, when the clutch is released and engaged. The "problem" with the thicker discs is that when the cover is bolted down, there is very little "movement" left over for the "t" shaped pieces to move and allow the actual pressure plate to lift off of the rear disc. (This lack of movement influences how far the intermediate plate can move, also.)
Fortunately, the two clutch discs from Roger that I tried were extremely "flat" (almost no run out) and I had no problems with the clutch releasing, when using a "late" intermediate plate. (Although I would have bet money that it would not have released properly, when looking at it.) I have no idea how this is going to work, when using an early intermediate plate.
These "issues" are going to influence how well the clutch releases....and will get "worse" as the clutch warms up.
I do not see how any of these issues would make noise.
The original early forward clutch disc had no Marcels. The rear discs all had Marcels. (These are the "flat" springs between the two clutch disc surfaces, which compress when the pressure plate pushes on the discs.) The Marcels are what make clutches smooth, when they engage. The "original" intermediate plates had .9mm to 1.0..of "potential movement" between the "H" stops....which was enough to lift the intermediate plate free from the front clutch disc (which did not expand when the pressure was removed.)
When Porsche superceeded the front clutch disc to the current style (with Marcels), they also superceeded the intermediate plate to the current version, which has a "potential movement" of 1.3mm to 1.4mm between the two "H" stops. This "increase" in the movement distance was changed, because the clutch disc "grew" when the pressure was removed from it (the Marcels expanded) and the .9mm to 1.0mm distance was found to be inadequate, which caused the front disc to "drag" and wore out the synchros very quickly. (Also wore the front disc more than the rear disc, since it was "dragging".)
So....there is definite "potential" for the front clutch disc to "drag", when the front disc is changed to one with Marcels, if the original intermediate plate is used. I've fought this problem dozens of times over the years....and finally gave up....I always use the "later" intermediate plate when the front clutch disc is changed to one with Marcels.
The "thicker" clutch discs that Roger supplies makes this problem more complex. When the clutch is bolted together, the actual internal pressure plate in the clutch cover, is forced towards the rear of the car. There are 3 "T" shaped pieces that keep the actual internal pressure plate centered. These "T" pieces go through the aluminum part of the clutch cover and move back and forth, when the clutch is released and engaged. The "problem" with the thicker discs is that when the cover is bolted down, there is very little "movement" left over for the "t" shaped pieces to move and allow the actual pressure plate to lift off of the rear disc. (This lack of movement influences how far the intermediate plate can move, also.)
Fortunately, the two clutch discs from Roger that I tried were extremely "flat" (almost no run out) and I had no problems with the clutch releasing, when using a "late" intermediate plate. (Although I would have bet money that it would not have released properly, when looking at it.) I have no idea how this is going to work, when using an early intermediate plate.
These "issues" are going to influence how well the clutch releases....and will get "worse" as the clutch warms up.
I do not see how any of these issues would make noise.
Last edited by GregBBRD; 05-31-2019 at 12:14 AM.
05-31-2019, 12:04 AM
#20
Former Sponsor
Worth thinking about:
If there is wear on the short clutch shaft (a "ridge" on the splines), and the new clutch discs sit in a slightly different position than the old discs (new discs will always sit in a different position and thicker discs will obviously sit in a different position, the new discs can "hang up" on those "ridges" (this wear is a major reason why we install new short shafts.). This, alone, could make a rattling noise, when the clutch is released. It could also "force" the clutch disc to drop into the "old" ridge and make the clutch disc "drag" on one of the metal surfaces, which would make the clutch not completely release.
I can see this getting worse, as the clutch pieces get hot.
If there is wear on the short clutch shaft (a "ridge" on the splines), and the new clutch discs sit in a slightly different position than the old discs (new discs will always sit in a different position and thicker discs will obviously sit in a different position, the new discs can "hang up" on those "ridges" (this wear is a major reason why we install new short shafts.). This, alone, could make a rattling noise, when the clutch is released. It could also "force" the clutch disc to drop into the "old" ridge and make the clutch disc "drag" on one of the metal surfaces, which would make the clutch not completely release.
I can see this getting worse, as the clutch pieces get hot.
05-31-2019, 01:00 PM
#21
Drifting
Great thread. I'll be tearing into my '78 sometime this Fall or Winter so this is more for me to lookout for....
05-31-2019, 01:50 PM
#22
Pro
06-01-2019, 10:19 AM
#24
Drifting
Greg,
Is your short shaft compatible regardless of which version of clutch discs are in the car? I don’t know what my car has (I assume they’ve been updated) but am working on stockpiling whatever pieces I can in anticipation of the project.
Is your short shaft compatible regardless of which version of clutch discs are in the car? I don’t know what my car has (I assume they’ve been updated) but am working on stockpiling whatever pieces I can in anticipation of the project.
06-03-2019, 09:15 PM
#25
Rennlist Member
Thread Starter
Okay - I've gone through this as it relates to my situation. I have a new pressure plate, of which the design has not changed. I have the original "early" intermediate plate which has been surfaced on both sides that allows for the 0.9 to 1.0 mm potential movement. I have new clutch discs from Roger which are thicker than the original discs and which have the "Marcels" in both discs so that may be a problem. I have a new TOB which needs a new snap ring. I also have what appears to be the original stub shaft that has some wear on it but not that bad.
So, I am going to order a new stub shaft from Greg to eliminate that variable. I am going to install it as Stan has suggested. I am going to order a new clutch guide tube and a new snap ring for the TOB. I am going to inspect and maybe order new pinch bolts front and rear but make sure all are torqued before I drive the car. That only leaves the front disc and the intermediate plate. Getting a new intermediate plate will be impossible I think.
I looked closer at my old front clutch disc and it does not appear to have the same spring load, the Marcels, as the second disc so I see what Greg is saying. The original part number is 928.116.011.23 for the front disc - probably impossible to find - looks like superceded to 928.116.011.35. So I am going to see what I can find without breaking the bank.
So, I am going to order a new stub shaft from Greg to eliminate that variable. I am going to install it as Stan has suggested. I am going to order a new clutch guide tube and a new snap ring for the TOB. I am going to inspect and maybe order new pinch bolts front and rear but make sure all are torqued before I drive the car. That only leaves the front disc and the intermediate plate. Getting a new intermediate plate will be impossible I think.
I looked closer at my old front clutch disc and it does not appear to have the same spring load, the Marcels, as the second disc so I see what Greg is saying. The original part number is 928.116.011.23 for the front disc - probably impossible to find - looks like superceded to 928.116.011.35. So I am going to see what I can find without breaking the bank.
06-04-2019, 10:07 AM
#28
Nordschleife Master
Yeah. The shaft on the right is the wear Greg was talking about a couple posts back.
That shaft is trashed.
It's also the 'poster child' for proper use of the 'super duper sticky clutch shaft grease' that is supposed to be put on during installation.
That stuff has a proper name (Optimoly?), but, as with a lot of things, just call or e-mail Roger and ask for the 'super duper sticky grease' and he'll know exactly what you mean.
That shaft has very obvious and visible wear. My understanding is that it doesn't have to be that bad to be a problem. If you can run a fingernail up and down the splines and it catches anywhere, it's a problem.
That shaft is trashed.
It's also the 'poster child' for proper use of the 'super duper sticky clutch shaft grease' that is supposed to be put on during installation.
That stuff has a proper name (Optimoly?), but, as with a lot of things, just call or e-mail Roger and ask for the 'super duper sticky grease' and he'll know exactly what you mean.
That shaft has very obvious and visible wear. My understanding is that it doesn't have to be that bad to be a problem. If you can run a fingernail up and down the splines and it catches anywhere, it's a problem.
06-04-2019, 02:40 PM
#29
Former Sponsor
Wow, your shaft was terrible. Whenever there is rust inside the clutch discs, you will probably need a new shaft. (Rust between two metal parts comes from tiny amount of metal being "torn" off (wear.)
Special high pressure grease is absolutely mandatory on the splines!
Special high pressure grease is absolutely mandatory on the splines!
06-04-2019, 02:42 PM
#30
Former Sponsor
Yes, with the exception that there is apparently a super early '78 version with a very strange short shaft. I have a new one, but have never seen another.....could be from a prototype, for all I know. Just a "curiosity part", right now.