'79 4.5 928
The clutch was slipping in my racecar so I took it out and have glaze busted the plates. The friction plates were worn but not to the min according to the wsm. I had a set re-lined anyway.
Having put the whole lot back together, and yes, I did reset the stop plates, we fired it up yesterday and it will not engage gear. At all.
Having stripped it and measured everything I am a bit puzzled because it looks like the whole lot is refusing to disengage because of 1/2mm of plate.
I think the new plates should be 0.235" or 8.25mm in my money, I measured the new plates uncompressed (8.2-8.9mm) and then compressed (8.06-8.08) . The old one is already compressed and measures 6.87-7.00mm. The big difference in the new plate uncompressed is due to the springs holding the plates.
I think I have set it up right, pulling the stop plates out fully and evening them up.
The release arm ball joint and cup are fine - we did notice that the release arm moves about 4.5mm before eengaging the release bearing and put a spacer in temporarily to see if it made a difference. No
The slave cyl was bled, and starts to move as soon as the pedal is depressed, but it appears that the total movement is only 14.5mm and not 17.4 as per wsm. Can't find why as the cyl is ok and the pedal was set right before. I have noticed that the clutch has never engaged until right at the top of its travel, but I think this is normal in the 2 plate clutch cars.

I am going to put the old plates back in, but has anyone got any ides/suggestions?

 

was the master replaced??
if so then there is a chance the new part isnt the same as the old one IE the new MC stroke is about 5 MM shorter the trick is to cut off the tip of the MC piston by 4 to 5mm this should restore piston travel.
only thing to watch for is that the return spring in the MC can sometimes shatter from being over compressed, make sure the MC is also adjusted for proper preload and the clutch linkages at the pedal are all tight

 

Yes, the piston was replaced, but the old master cyl barrel was left in.
Are you saying that the new pistons are longer? That would explain the lack of movement.

 

Richard, This doesn't seem right:

The spring in the slave should take all of the slack out of the system-- so that the first incremental movement of the pedal and master starts pulling on the pressure plate. Is there possibly a missing spring in the slave?

Also make sure that the master piston is coming all the way up, so that the refill-hole is uncovered. In the "resting" state the slave-spring should take all of the slack out of the clutch components, and the master-spring should push the pedal all the way up and add fluid as needed. The pedal linkage needs to be adjusted per WSM for no free play between pedal and master.

And yes, new MC pistons have a longer "boss" on the spring end that acts as a stop, to limit travel for the later single-disc clutch.

 

Jim,

That comment does seem fine if he is doing the measurement with the lower bellhousing off, and the slave arm not resting on it.

 

Guys
The measurement was with the bellhousing in place and the slave connected - ie the slack is out of the system. The pedal is coming all the way up. I might take the master cyl apart and swap the seals onto the old piston to get some more movement.
I'm not sure whether to put the new plates back in though - I haven't got a 4 post lift and it is a bugger of a job on the floor. I only really want to put it back once more. The engine is being pulled anyway after the next race.

 

I just swapped the seals on mine using a rebuild kit from Porscheshop.co.uk, much cheaper than a new master. Good luck with the '79.

 

did you adjust the H tabs on the Intermediate plate. this is EXACTLY what happens when it is out of adjustment. you will never get it in gear, its impossible. however, once you are rolling down a hill or something, you can get it in 1st, and then you should be able to shift decently, to the upper gears with the clutch, although still a little knotchy. now, come to a stop and you are hosed. Also, you can start the car in gear and then let the clutch out normally to accelerate. that is the smarter test.

the H tab should have abotu a .25 to .5mm gap as you look at it with the bell housing removed. (or you can cut a hole and check and adjust from that.

mk

 

If the clutch pedal is moving through its full range (i.e. small play between the push rod and m/c at the top, and against the floor at the bottom), but the release arm is not moving the correct amount, you need to bleed the system again with the slave off, bleed valve up, and rod pushed in.
Until you get the full movement at the release arm, there's no point looking for any other problems.

Smiffy