hupp

For a '79 928 - double disc clutch:

My clutch recently began to drag. This problem does not rear it's ugly head until I've been driving a bit (about 10 miles or so). Essentially, the clutch does not drag until everything is good and warm then the issue begins, and gradually gets worse the more I drive. First the drive train takes a while to slow down and the issue progresses until depressing the clutch has absolutely no effect whatsoever. Next morning the clutch releases as it should, but after warm it begins to drag again.

I replaced the entire clutch pack about 300-500miles ago and it operated fine until recent. (New PP, IP, discs, release bearing, pilot bearing, center shaft and flywheel machined.) The hydraulic components have also been replaced - master, slave, blue hose and black rubber hose under the car). I've been under the car multiple times checking/adjusting, checking again and adjusting again with no success.

Hoping one of the double disc gurus can give me some advice, but do have one specific question regarding the splined shaft. How easy should it be to move the shaft back and forth. I did use a liberal amount of moly htl as specified but it takes a little effort to move the shaft. Should it move very easily if properly centered and lubed?

Thanks, in advance, for the help.

GlenL

The "hot and does nothing" part says it may be hydraulic.

With all newer parts on there the obvious cluprits (inter. shaft, slave, master) are no longer obvious.

My suggestion is to get it hot and then observe the clutch action through the access hole. Arm moves? Then it's adjustment or intermediate shaft. No movement? Then it's slave or master.

FlyingDog

Maybe release/throwout bearing, but more likely hydraulic as Glen mentioned due to this being a hot issue.

What do you mean by move the shaft? The discs should slide very easily on the shaft. The shaft should be locked to the draftshaft with the pinch bolt and should not move. You say you replaced the shaft. Did you get the newer nickel plated version?

hupp

Flyingdog,

I removed one of the pinch bolts on the collar and slid the shaft just to re-check the alignment. The shaft was ordered new fro 928 Intl, and had more of a silver luster to it, rather than, the dark grey coloring like the old - which needed to be replaced due to worn splines.

I'll check for air in the system tomorrow and bleed one more time for good measure. A hydraulic issue would make sense, but why would the new clutch operate fine for about 500mi then suddenly exibit these issues. Seems like hydraulics would cause problems from day one. Maybe an ellusive air bubble finally migrated to the slave cylinder or master cylinder.

1slo928

maybe you hose from the brake resivoir to clutch master cyl is leaking I replaced mine it was a miserable job but I wanted to replace all the hoses for the system since my car is 27 years old.
Chris

hupp

Chris,

The blue hose is new. I also gave it a good look when I was under the shark yesterday -- dry as a bone.

I'm beginning to suspect that I may have installed the discs backwards - Disc I (thinner disc) near PP and disc II (thicker disc) near flywheel. I'm going to have another look this afternoon. I'll probably just pull the clutch and thoroughly inspect everything -- almost have to do this for peace of mind.

FlyingDog

I have heard of people having hydraulic problems from leaky brake master to resevoir seals (doesn't make any sense, but seems to happen). Also, just because the blue hose is dry doesn't mean it's not pulling in air (Did you hose clamp it at both ends?).

Since it started after 500 miles, I'd guess throwout/release bearing. The silvery intermediate shaft should be the newest version. I don't know about 79, but I don't think you can put the discs in backwards in newer ones and have the clutch work.

hupp

I can see where a bad pilot bearing may cause "clutch dragging type symptoms" since the assembly basically rotates around the friction discs/splined shaft when released. Its possible that a failed pilot bearing would essentially turn the drive shaft because it would be somewhat fixed to the flywheel. I do not understand how a bad release out bearing would cause the clutch to drag. But nevertheless, no bearing groaning/rattling/squealing is evident when the clutch is engaged or released.

FlyingDog

I think the problem is that the throwout bearing is not pulling the clutch far enough back to disengage. That was the problem on mine, Beerfish's and I think Hacker-Pschorr's.

hupp

FlyingDog,

Was it a failure of the snap ring that holds the bearing in place?

FlyingDog

On beerfish's, the keyed ring that pushes on the pressure plate fingers was eating it's out out of the bearing. Mine did not look like it was seriously damaged on the outside (a little movement of the keyed ring and snapring), but the bearing inside was destroyed.

My pilot bearing was also dragging, but beerfish's was fine.

hupp

Well...I do not suspect an issue with the release bearing. Everything was in good order upon the last assembly. I'll be pulling the clutch in a couple of hours -- at this point I hope something obvious jumps out at me. But that is usually never the case.....

hupp

I was able to take the clutch down yesterday and did not find anything terribly obvious. Here are some things I did notice:

- Before removing the clutch pack, I removed the rear pinch collar bolt (TT bolt) and slid the splined shaft back and forth to check lubrication. It slid very easily initially. My helper turned the engine by hand by about 45 degree incriments and I checked the shaft movement at each increment. What I found was that the shaft would slide easily in some positions and not so easy in others. But it would not completely bind.

-- Noticed that the end of my TT shaft had a bit of radial play in the up and down direction but not in the side to side direction. Enough to get my attention. This TT is a rebuilt unit with about 1000mi on it. Nothing was too concerning ere though

--Upon disassembly, I observed ecerything to be in the right order, all bearings good, IP adjustment rivots still tight -- nothing out of the ordinary. Cleaned and re-lubed necessary points.

--When installing in the car, my astute helper noticed that the guid sleeve was hanging up on the shoulder of its mounting location, and was not sitting flush on its seat. Its very possible that this was the case during the last install and I did not catch it.

--After re-installation/shaft centering/adjusting we repeated the first step above and the shaft moved very easily in all crank positions.


I'll spend some time this afternoon checking the adjustment and re-installing the exhaust -- then hopefully have a successful test drive.

nemo

Ive had a similar problem on my 80, hard to shift up and down when warmed up/hot.
A week ago i lubed the splines ( they were dry ) on the shaft for the cluch disks and it become much better, but i think the sync rings now are worn so its not perfect.

hupp

Clutch is back in and problem still exists -- dragging after hot!

In an effort to continue to troubleshoot I was thinking of machining a new slave rod, which would be approx. 1/8" longer than stock to effectively increase travel. Not a permanent fix, but to see if travel is an issue -- What unintended adverse effects could this have on the clutch? Would this be a stupid idea?