Another M52'd iS problem - clutch control this time...

[Aubs]

Before I start on another problem, I have to thank DanThe for his help with the cooling system issues. Got rid of the air in the end by seperating the components and bleeding them one at a time. Thanks for the tip mate!

Right, I'll tell the whole story here for clarity, and summarise the points at the end:

Couple of weeks back I was happily driving along near my house, driving quite sedately. Changed to 3rd, everything is fine, reached for 4th and suddenly there is no clutch pressure - return spring works fine but the pedal is limp and clutch does not disengage. No funny noises - this happened suddenly and completely silently.

I got the car home and had an investigate: no loss of fluid at all, on first inspection everything appears normal. I removed the slave cylinder and got a mate to press the pedal while I held the slave in the 'return' position - nothing, I could feel no change in pressure (it should be much stronger than my hand right?). tried this by taping the slave back as well then pushing the pedal (just to double check), the tape stayed intact.

Thought then that there may be air in the system (not that I had any idea how it would have suddenly filled with air). The bleed nipple on the slave was just shooting out fluid - no air.

I then watched the level in the fill pot while I pushed the master, it rose almost to overflowing. Repeating the process with the slave only caused it to move 5mm or so. From this i assumed the seals in the [5000 mile old] slave had gone.

Got a new slave and new fluid, fitted the slave and filled with fluid with bleed valve OPEN. Bled in usual way for approx 15 minutes, until I had just fluid flowing from the valve. Absolutely no clutch resistance at all.

Then tried operating the pedal myself, when released I noticed a gasping sound, coming from the filler bottle. A closer inspection showed that it has a split in the side of the screw on cap. Air was being drawn in on the release. Surely this isnt right I didnt think this end of the circuit was pressure dependant?

Summary:

- The slave cylinder is new
- There are no fluid leaks anywhere
- The master cylinder piston appears to displace fluid in the filler bottle just fine
- The slave isn't being activated by the master

A thought I just had - does the master have a non return valve fitted that prevents the fluid just being pushed up to the filler bottle, rather than activating the slave?

Sorry about the overload of information chaps - just want to make sure I get everything down first off. As always, any help is greatly appreciated

[HairyScreech]

sounds like your bringing air into the split and then into the master.

[Aubs]

I was told by a mechanic at my local garage (not E30 specialist) that they always bleed clutch systems with filler cap off, and that it shouldnt make any difference. I saw that the cap was not o-ring'd or pressure sealed in any way, so I assumed this was true?

If the system was dependant on the seal at the top for holding air pressure, surely the air in the space of the reserviour would be compressed preferentially over the fluid - meaning that the slave still wouldn't move?

[DanThe]

The master needs changing mate, that is where your problem lies. The res cap is vented so it wont make any odds if its on or off

[Aubs]

The master needs changing mate, that is where your problem lies. The res cap is vented so it wont make any odds if its on or off

Sounds likely doesn't it? What about the fact that it still displaces fluid in the bottle though? The bias of flow can't be equal to that and the slave can it?