Clutch differences
12-24-2007, 01:39 AM
#1
Three Wheelin'
Thread Starter
Join Date: Sep 2003
Location: SF Bay Area
Posts: 1,526
Likes: 0
Received 0 Likes
on
0 Posts
Clutch differences
I am working on a 78 with a bad clutch. The guy managed to tear up everything including breaking the ball, scoring the flywheel and intermediate plate.
I have secured a new pressure plate, the two disks, a used updated clutch arm, a new ball and socket and some used parts.
The guy I was buying the used parts said they came off a 79, but when I get the flywheel and intermediate plate they are from a newer car. The intermediate plate and the flywheel use pins while the 78 flywheel has a rim around the flywheel to center the pressure plate.
Now I get all these parts and lay them out. I have the 78 parts, a second flywheel from an 82, the flywheel the guy sent me and even parts from an 86 clutch. Here is the deal - other than the pin in the pressure plate I can see no difference in the plate between the 78 and the new one - except the locating pins. The same with the Intermediate plate. Given the clutch plate slips down into the intermediate plate I see no real reason for pins on this part.
When putting the parts together and measuring the deck heights I come up with the same thing. It look like the lip on the flywheel has just been machined off on the newer flywheels and holes drilled for the pins.
I see no reason using the Intermediate or flywheel as a guide why I cannot drill locating pin holes in the 78 pressure plate and go from there.
In examining the disk I do not see much different between the two disks on the 78. They are different part numbers. The only difference appears to be the spacer between the two fiber pieces is a little thicker in one of the disks. When I look at a newer disk set the spacer difference is reversed. On the newer plates one of them has an extension on the spline part.
Has anyone been into this mess before and have a better understanding than I do? It looks to my inexperienced eye one could mix and mingle the parts without too much concern.
I notice 928 Specialists sell mounting bolts for the clutch and the flywheel. Are these items that need to be changed out with each change?
Thanks a bunch - that is if anyone is still reading this list
Merry Christmas and Happy Holidays.
Dan the Pod Guy
I have secured a new pressure plate, the two disks, a used updated clutch arm, a new ball and socket and some used parts.
The guy I was buying the used parts said they came off a 79, but when I get the flywheel and intermediate plate they are from a newer car. The intermediate plate and the flywheel use pins while the 78 flywheel has a rim around the flywheel to center the pressure plate.
Now I get all these parts and lay them out. I have the 78 parts, a second flywheel from an 82, the flywheel the guy sent me and even parts from an 86 clutch. Here is the deal - other than the pin in the pressure plate I can see no difference in the plate between the 78 and the new one - except the locating pins. The same with the Intermediate plate. Given the clutch plate slips down into the intermediate plate I see no real reason for pins on this part.
When putting the parts together and measuring the deck heights I come up with the same thing. It look like the lip on the flywheel has just been machined off on the newer flywheels and holes drilled for the pins.
I see no reason using the Intermediate or flywheel as a guide why I cannot drill locating pin holes in the 78 pressure plate and go from there.
In examining the disk I do not see much different between the two disks on the 78. They are different part numbers. The only difference appears to be the spacer between the two fiber pieces is a little thicker in one of the disks. When I look at a newer disk set the spacer difference is reversed. On the newer plates one of them has an extension on the spline part.
Has anyone been into this mess before and have a better understanding than I do? It looks to my inexperienced eye one could mix and mingle the parts without too much concern.
I notice 928 Specialists sell mounting bolts for the clutch and the flywheel. Are these items that need to be changed out with each change?
Thanks a bunch - that is if anyone is still reading this list
Merry Christmas and Happy Holidays.
Dan the Pod Guy
12-24-2007, 01:09 PM
#2
Nordschleife Master
I have done clutchs in other cars, and none of them have had locating pins or a lip on the flywheel to locate it.
I personally cant really see a reason as to why they are even required.
As to replacing the bolts, it is not a must to do, but you can if you like.
I personally cant really see a reason as to why they are even required.
As to replacing the bolts, it is not a must to do, but you can if you like.
12-27-2007, 01:21 AM
#3
Addict
Rennlist Member
Rennlist Member
I know one clutch where different year parts were mixed and pins used. Works ok. I would drill holes for pins.
Centering pins aren't there just for fun. For example one GTS had really anoying vibration which varied at based on engine revs. It took long time for owner to notice single disk clutch didn't have those three pins installed. Before he found this out he went through TT bearing change and many sleepless nights thinging if he should pull entire engine to pieces or not to find the cause.
Centering pins aren't there just for fun. For example one GTS had really anoying vibration which varied at based on engine revs. It took long time for owner to notice single disk clutch didn't have those three pins installed. Before he found this out he went through TT bearing change and many sleepless nights thinging if he should pull entire engine to pieces or not to find the cause.
12-27-2007, 10:04 AM
#4
Burning Brakes
The older double disc clutches are diametricaly centered (via the lip) and the newer double disc clutches are dowel centered. Although everything looks very close in size they are not. The dowel centered PP will not squeeze into a diametrically centered IP - the outer diameter of the dowel centered PP is slightly larger than the diametricaly centered PP. I found this out when replacing my clutch -- the PP's looked the same but when my new one would not stack I looked closer and noticed the holes for the pins - I had to send it back and order the correct part. So, "on the flip side", it stands to reason that there may be a bit too much tolerance when you stack your diametrically centered pp inside your dowel centered IP -- modifying and centering may be tough.
The clutch friction disc design, Intermediate plate (more travel specifically), splined shaft and guide sleeve were changed at some point in the early eighties. Basis your description, I think you have aquired the newer design friction discs - difference in liner spring thickness is usually older design. With the newer design one disc (PP side) should have the longer hub.
The newer and older parts must not be installed together or the clutch will not release properly.
The clutch friction disc design, Intermediate plate (more travel specifically), splined shaft and guide sleeve were changed at some point in the early eighties. Basis your description, I think you have aquired the newer design friction discs - difference in liner spring thickness is usually older design. With the newer design one disc (PP side) should have the longer hub.
The newer and older parts must not be installed together or the clutch will not release properly.
