Clutch Sticking & Clutch Master Cylinder. LHD / RHD ?

bmnelsc · Jul 31, 2021

I have had experience with clutch sticking due to the release bearing being worn AND sticking on the guide tube which also wears. Upon disassembly the bearing was found to have A LOT of thick grease which didn't really help. If this is your issue - time to replace the release bearing AND GUIDE TUBE...prolonged usage in this state will wear syncros quickly as while it seems to release the clutch OK it really isn't and excess friction is created. There have been posts here where people have been lubricating their guide tube with some success but it is difficult and only delays the inevitable - parts replacement.

The other issue you may be experiencing is rust/corrosion on the input shaft causing the clutch disc to hang up momentarily. Trouble is it is virtually impossible to observe this with the very limited access provided by the inspection port. Too bad Porsche didn't include a removable section on the bell-housing so we could actually see in there...

The manual includes specification for clutch and pedal travel and disc thickness measurements. You should be checking all of these as well as you may be due for some parts any way.

In summary - don't screw around trying to grease your way out of this or assume that throwing new cylinders at will fix it (the clutch specs in the manual will show if cylinders are required)...the longer you leave it the more damage you are doing to your transmission even if it doesn't feel like it. A clutch is cheap compared to a gear box overhaul!

BenEngland · Jul 31, 2021

Hi.

On the few occasions that I have driven the car this year, since being pretty much laid up for winter, I have had a slight problem with the Clutch.
Appears to be sticking for a fraction of a second in the disengaged position ie. Boot it, change gear & clutch does not immediately re-engage. Pedal does not immediately come back up & clunks a bit.
This appeared to improve as it was driven on each journey.

Initial thoughts were perhaps the Clutch plate was sticking on the shaft splines due to corrosion / lack of use ? & that using it would free it up, which it appeared to do.

However last time out the Clutch pedal became exceedingly stiff & took excessive effort to depress, felt like a mechanical problem & really thought that I wasn't going to get it home, freed up slightly on the way back.

Initial thoughts are to bleed the system & maybe replace Slave & Master cylinder as this would be the cheapest option against going for replacement clutch, Clutch release Fork, Bearings etc which is a last resort due to cost, (I'm too long in the tooth to tackle major under car work these days).

However looking at various suppliers online there appears to be a caveat on some listings that the Master Cylinders are for LHD vehicles ?
They all look to be symmetrical so wandering if anyone has experience of using these ? (the type that has the plastic nozzle at the bulkhead end of the cylinder)

Regarding the clutch has any one experienced anything like this ? Advice very much appreciated.

Car is a 1988 2.5 Turbo

BenEngland · Aug 2, 2021

Hi Bruce.

Thank you for your reply & advise, you are sort of pointing me in the direction of my worst case scenario, that being removal of gearbox, torque tube & clutch bell housing to investigate the components that you have indicated as being the possible cause. As car has done 130K then whilst all that is removed a full clutch replacement would be the obvious thing to do.

However before I consider that I will check the clutch travel travel etc against the manual specs as you suggest.

If all that checks out I will probably remove the Master Cylinder & check that over to make sure that all internal parts are OK, (springs ?). May as well do this as I intend to replace the fluid & bleed it out in any case. Master cylinder was replaced in 1997 so done about 55K since then.

Of concern is to why it took so much effort to depress the Clutch pedal the last time that I drove it, (which is why I want to check for broken internal spring), though it appears to require only normal foot pressure at the moment ?

Sort of clutching at straws I know but don't fancy doing the clutch job, although probably just putting off the inevitable!!

John E

bmnelsc · Aug 2, 2021

Hi John...the symptom of "hard to depress" points directly to friction either from rust on the splines of the input shaft/clutch hub or release bearing on the guide tube. The "not engaging" right away until driven a bit also points to the clutch hanging up either from the input shaft/hub or release bearing on the guide tube. I suppose it is possible that the clutch release fork is failing. The other potential although unlikely source of this kind of behavior would be the pedal itself hanging up on its pivot shaft due to failed bushes, etc. I would think this unlikely and you should be able to detect some slop in the pedal if that was the case. IMHO failing master or slave cylinders would not behave as you describe - they are merely hydraulic cylinders after all and the usual failure mode is to not compress fluid (seen as failure to activate the clutch) or to not hold pressure (clutch depresses but releases on its own as the pressure bleeds off).

My experience was much like yours with hard to depress and occasional failure to engage after a shift. Some high RPM therapy loosened things up - temporarily... I too am "long in the tooth" and not able to do much or my own work anymore - particularly when it comes to getting the car up on stands and crawling around underneath. Your best bet is to get some quotes from experienced shops and pick one. Get the work done or DON'T DRIVE THE CAR. My procrastination left me with a weak 2nd gear synchro with an estimate of at least CDN $2500 to repair. If I kept going I probably would have a much larger repair bill. This on top of the clutch job. You decide but I assure you it is a false economy to try to work around this.

As you are aware, our 944s are the classic examples of "while you are in there might as well replace ..." which I think is wasteful but the time/labor cost associated with accessing the clutch means you really need to address all suspect wear components at the same time. Having to take it all apart again to replace a spigot bearing or guide tube or release fork a year or two after a clutch replacement is just too expensive especially for those of us that can no longer do it ourselves. Good Luck!

BenEngland · Jun 24, 2022

Update.

Situation regarding the clutch pedal sticking & not releasing the clutch became so bad the last time that I used it, after a winter of not being used, such that I was unable to pull away at trafic lights on a slight incline leaving my local supermarket as the clutch would not engage, embarrasing or what !!

A friend had speculated that the Release Fork Bearings may have siezed, seemed plausable?

First attempted to bleed the clutch with the aid of 'Ezibleed' - Flow rate of fluid appeared to be very low?

Decision made to replace Clutch Master & Slave Cylinders - Slave Cylinder was sticking slightly but confirmed that release bearing not siezed.

Slight improvement but still not right & still, in my opinion, insufficient flow rate of fluid during bleeding.

Only part left to replace now being the flex / hardline from the Master Cylinder, (£117 from OPC), as previously stated by another poster this has been re-designed in that the hard line is now much longer which takes the flexible rubber pipe further away from the heat of the exhaust.

Installed & Bled out using the 'Ezibleed' at about 15 Psi - no problems bleeding, didn't have to raise the rear wheels, tapped the Master & Slave Cylinders with a hammer to release any trapped air each time prior to opening the bleed valve. Appeared to be pretty much straight forward, or was I just lucky? Used about 3 litres of Fluid.

Upon inspection of the old hard line there was a blockage at the end of the hardline, can't say exactly what as it fell on the floor & i couldn't find it.

Inspected the old Master Cylinder & there was a lot of 'black gunge' at the bottom of the cylinder. Can only imagine that over time this had found itself into the hardline & been baked by the heat of the exhaust until it formed a hard pellet that caused the blockage. I suspect that this had built up slowly over a number of years & did't get noticed until the car was virtually undrivable

Moral of this has to be to change the clutch fluid at regular intervals.

dlknight · Jun 24, 2022

Glad to hear you sorted it, I couldn't remember the last time my clutch fluid had been bled and so did it back in 2020 and it came out black. It was OK for the limited driving I did back then but then I've had it in the garage since doing my restoration work and it began to drip clutch fluid all over the floor. The slave cylinder was completely shot, seal had blown out and the cylinder bore is slightly corroded. The master cylinder looks original so my thinking it that the seals perished and mixed with the clutch fluid. Possibly similar to what happened to you. I have to replace the hard line from the master to slave as the nuts rounded on the slave cylinder side and I had to get a vice grip on it to remove. Going to make up my own line as I'm also doing the rear brake lines.

Waylander · Jun 25, 2022

Everyone changes the brake fluid but never the clutch and that absorbs just as much water as the brakes, hence the horrid black stuff seriously corroded slave cylinders and blocked pipes, it’s a thing that’s nearly always missed as it’s such a pain in the

BenEngland · Jun 25, 2022

Regarding the Coupling / Flare nuts rounding off.

When I did the Job I initialy had a proper Flare Nut Spanner but it was 'Bi-Hex' design and I could feel the nuts starting to round off. Bought another Flare Nut Spanner, this time being a 'Hex'

Design, far more 'meaty' & grips all of the flat on the nut, not just the corners, so does not tend to round the nuts off - worth while investing in one.