Clutch advice needed plz
 

Just the other day I started having some troubles with the clutch on my 78 928.

It's still the double disc configuration that I just rebuilt/replaced a couple months ago. I did have a reputable shop do that actual installtion. We replaced the slave cyl., clutch dics', intermidiate plate, pressure plate and resurfaced the fly wheel.

Now I am intermittantly having a clutch pedal that is "hanging up" for lack of a better phrase. Seems to happen after prolonged driving before hitting the clutch (7 or more min) and does not happen when the car sits.

When the clutch is depressed, generall about half to 2/3rds of the way down it becomes very stiff, similar to the brake pedal when you are about to lock all the wheels. With enough force it will go all the way to the floor and I believe I can hear a noise when the fault occurs.

It does seem as if the clutch is released when the pedal "hangs up" as it shifts effortlessly out of gear. I have been hesitant to engage it into gear as of yet, but plan to try it the next time the fault happens.

After a couple (two to three) full clutch engagements and disengagements it returns to "normal" opperation.

Other background...
The clutch master I seem to recal had new guts put in it over a year ago and the cylinder walls were reported to be in good shape.

The car also has the early steel ball clutch arm pivot and not the newer 10mm with bushing ball.

It has been hot the last few days and I have headers on the car for the first year too. The headers have NO header tape on them.

Any thoughts would be much appreciated.

I'm no expert.. but I'll give my 2 cents
When I did my clutch on my '85 I noticed some galling on the guide tube that the throwout bearing slides on. The clutch had a kind of sticky feel to the pedal before i took it out.Kind of felt like you describe but more on the release. So as I didn't get a new guide tube I just polished it up in the lathe, replaced both discs and throwout. Definitely smoother..
Wish I'd done the pp also as the clutch is still kind of weak!
Look me up if you're out in the valley
Darrin Gilmore
Sardis B.C.
jdgilmore@shaw.ca
1985 928s 5-speed

OK, lets look at the whole system:

- Clutch Pedal: you’ve got bushings, bearings etc. If these bind you’ll have trouble pressing all the way. These parts are often worn on older cars.

- Clutch Master Cylinder: This is something that you didn’t replace. It so happens that it is one of the greater pains in the *ss to remove. Either you pull the brake master/booster to get clearance or drill a hole in the fender well (actually, the preferred solution!). The odds are that is the original clutch master cylinder in your car and it could be binding. Some shops attempt a rebuild by leaving the cylinder in place. This may work once, but on an older clutch master it won't work.

- Clutch Slave Cylinder: you replaced it, but is the rod binding? Pull the inspection plug to see if it the actuation rod aligned is OK.

- Clutch lever: This is the lever that actuates the clutch plate. It has a ball socket that it fits onto and the clutch slave cylinder move it. This can bind if it wasn’t installed correctly.

- Central shaft: the dual plate clutch moves over a short shaft. If the shaft was not replace with the clutch plates, and if it is worn, the intermediate plate can bind and you will not get proper clutch disengagement. I think this shaft is often overlooked in a clutch replacement.

- Clutch intermediate plate: a very expensive element of the dual plate clutch. Not much to go wrong, but if it and the central shaft become worn the clutch will never disengage correctly. Particular attention is needed to align this so it is equidistant between the two clutch plates. If a mechanic isn’t familiar with the adjustment procedure, the central plate can be DAMAGED and it cannot be repaired! HOPE that you don’t have to replace this part, it is expensive.

- Clutch Plates: yes, this is what you replace. The remaining surface distance is measured from the rivets. There isn’t that much material there.

- Pressure plate: This is what provides the “clamping” pressure on the clutch plates.

- Clutch thrust washer: If this little washer is installed backwards, it will wear out the fingers in the pressure plate. Be sure it is in the proper orientation! [if your mechanic doesn’t have the workshop diagrams, this is a very common mistake]

- Thrust bearing (AKA throw-out bearing): this is what is worn on each shift. If there is noise when you press in the clutch, this is most often the cause.

OK, all the bits have been described. The two plate clutch is a great mechanism. If all of the parts don’t work correctly, or the intermediate plate isn’t adjusted correctly, it can be a HUGE source of pain. When it works correctly, it is great. If you buy an old 928, the odds are the central shaft is worn … don’t over look that part.

You really need a mechanic that understands the two plate clutch to repair it correctly. Any other mechanic will probably not do it right! Be prepared to drop $1500 into it if all the bits need to be replaced!

Good luck

Thanks for the replies...
I had a 928 mechanic do the work as I was in a rush for it. But all components "down under" have been replaced and the intermediate plate is new and has been adjusted. It also has been working flawlessly for the last couple months.

All told it wasn't $1500, more like $2800.

The guide tube was replaced last year on another clutch work job and was still in good shape.

Even if it were worn, it is taking 3 to 5 times as much force to complete the clutch stroke as it would normally take.

It almost seems like the clutch gets to it's further-most travel before the pedal hits the floor.

All the cockpit mech is tight and opperating fine.

As mentioned the clutch master has had new guts oput in it and it had a good looking sleve at the time. I know it to be a REAL bastard to change that clutch master, that's why we just did the guts.

Thanks again.

OK...

MY CLUTCH QUESTION IS THIS.

I was told to always replace the intermediate plate...the biggin...the expensive part. ALWAYS.

Is this not true. Is this something than can be inspected and reused. I AM VERY PARANOID about creating vibration in the drive train. The intermediate plate seems like a place vibration can be introduced.

Chris Magid
1986 928s Garnott Red
camdsl@swbell.net

The intermediate plate "floats" between the two friction discs and really takes far less abuse wear than other components in the clutch assembly . Inspection is an option and if it shows no wear ridges or blue hot spots it can be used . It is not recommended to resurface as it is part of the stack which determines the clamping force of the pressure plate springs . Porsche trained technicians were tought to replace everything !!