9000 Aero clutch problem

[carrera]

My dads Aero has been eating clutches. I have now replaced 2 of them where the material has been ripped off one side - the last on after about 500 miles.

Last time I did this we bled the clutch and everything seemed fine. Then after a couple of hundred miles the clutch stopped working correctly. It did not disengage when the pedal was pressed.

At first I thought it would just want bleeding again. So, pressure bleeder in hand I have put the car with the front in the air and bled the clutch again this morning. The pedal seems good, there's about the right amount of pressure, but it is still not working correctly.

The strangest thing is that if I start the car in gear, with the clutch depressed, the engine runs, and the wheels do not turn. So far so good   

I then release the clutch and the wheels turn. Good too.

However, if I then depress the clutch the wheels continue to receive power and if I attampt to change gear there is either a grating, or the synchro engages and the car changes gear with power still being applied to the wheels.

Now the really strange bit.  If I repeat the exercise, by switching the engine off, the car will start in gear with clutch depressed and provide no drive to the wheels. Once released the clutch is engaged until the engine is switched off again.

The slave cylinder and master cylinder have both been replaced, and don't have many miles on them. (not to say one of them could have failed again). Similarly the flexi pipe has also been replaced.

The only thing I haven't done that I am aware of is reverse bleed the slave cylinder with a syringe.

Has anyone any ideas what is going on here - it seems to be more than the usual bleeding problems (or is it ?)

Thanks in advance

[Paul @ Kippen]

carrera,

It seems to me that you have a mechanical problem with the clutch, rather than a hydraulic one.  I think the clue lies with the fact that two clutch plates have lost the friction material from one side.  A little assymetric wear is normal, one side wearing slightly faster than the other but not to that degree.  I get the feeling that the flywheel may have a rough patch.  You did replace the pressure plate, didn't you ?

I think what is happening is that when the engine is stationary, the clutch disengages properly.  Once running, as soon as you engage the clutch, the roughness catches on the friction material and sort of 'locks' the plate to whichever side is the problem.

You might need to get the flywheel ground flat, or if it is the other side which gets ripped apart, fit a new pressure plate.

As I reread this I also would consider looking for a wear lip on the input shaft on the gearbox.  This could jam the plate against one side or the other.  If so you might get away with some gently filing of the edge of the 'lip but really you could be looking at a box rebuild and shaft replacement.

Paul @ Kippen.

[sgould]

I didn't comment before because I don't know the 9000 to any degree.  But my thoughts went to a notch on the splines on the input shaft.  I had something similar on a Morris Minor many years ago when the clutch dragged a bit on release. 

[carrera]

Thanks guys for the suggestions.

I ended up dismantling the old master cylinder (he still had it). The piston area had some green/brown "gunk" / sludge in it, which didn't really look like brake fluid at all.  After a good clean up, the seals etc looked fine, I swapped the master cylinders over and retested the car. There was no difference, so either the problem is not in the master cylinder or both are faulty.

I decided that rather than mis-diagnose the problem (and spend another weekend on my back removing / replacing the gearbox) I would have a word with my local dealer.

Current view is that the underlying problem is internal failure of the hose from the reservoir to the master cylinder, which leads to the green deposits which then prevent the master cylinder and slave cylinder working correctly. There was apparently a campaign to replace these hoses at some time.

I have dropped the car off with them this evening - will keep you updated

[Paul @ Kippen]

carrera,

Failure of the flexible section between the master and slave cylinders is fairly well known.  If you get an assistant to get their head down in the correct area they should hear a faint 'hiss' when the clutch pedal is held depressed.  However, in action, the symptoms are that you press the clutch, select gear and without lifting your foot off the pedal the clutch gradually self engages.  Pumping the pedal will disengage again.  Real fun in traffic !

Paul @ Kippen.

[carrera]

Well, the problem is found and fixed.

It turns out that I had been successful in bleeding the hydraulic system, and the pipe from the reservoir to the master cylinder was contaminated. That still did not fix the issue so it was gearbox out again. The clutch cover / diaphragm had fractured and completely broken in two places across the drive face, meaning that it was impossible for drive to be released.

Thanks to everyone for their ideas - it's the first time I've seen a completely broken friction surface, as opposed to cracked. 

[sgould]

That's unusual.  I wonder if the part was a recon unit that was rebuilt without a full inspection?  If it had had a hard life before recon, it might have caused some extra fatigue.