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MG MGB Technical - Clutch help please!

The clutch on my 67 BGT suddenly failed the other morning. The pedal started to loose resistance and very quickly ended up with only about an inch of active play in the bottom of the pedal before not allowing me to select any gear at all. I have since removed the slave cylinder and replaced the seals before bleeding the system. Slowly the resistance in the pedal returned but as soon as you turned the engine on it went again. With the engine on you can slowly pump the pressure back up again to allow you to put the car into a gear but still only with the bottom inch of the pedal being active - the clutch is very grabby at this point. The pedal will then go back to the floor and you have to pump wildly to allow you to put it into gear again. There does not seem to be any fluid loss from the master cylinder. One other factor is that if the car sits in traffic and gets very hot, you begin to feel a grinding through the clutch pedal and the clutch seems a bit resistant to engage drive for a moment but all worked perfectly when cool. I'm not sure if it is a hydraulic problem or whether it is the thrust bearings as I have been told by someone. I don't want to take the engine out if I can help it so would really appreciate some more opinions before deciding what to do!
Many thanks in advance.
Martin

Sounds like the clutch master cylinder is very close to being completely kaput.

Fortunately, it is not too difficult to rebuild and the kit costs is not unreasonable.
Daniel Wong

That's probably my next line of investigation before engine out I guess, but I figured that if the master cylinder was worn out then I would probably be losing fluid?
Martin

Have a look underneath the car at the slave cylinder and have an assistant press the pedal. Check for full movement of the arm and pivot fork. Do this at the various stages of your problem (cold and hot). If you don't have full movement then it is probably hydraulics. If on the other hand you have full movement at all stages, and your mention of the grinding makes me wonder, you may have a very worn clutch release bearing. What is the mileage and is it the original clutch as far you are aware. My clutch gave up at 120k miles (bearing and plate).
Also, get your assitant to pump the clutch pedal and look for any movement of the front crank pulley. If there is any movement, it may be a worn thrust washers on the crank.
You may be able to pull back the rubber grommet on the clutch fork and somehow, by peering into the clutch housing with a torch, ascertain what state the bearing is in, but tricky to say the least.
HTH
Martin.
Martin

Martin
The mileage is about 118k - not sure if it is the original clutch though. Whilst bleeding the system I was observing the fork going into the slave cylinder - it seemed to move about an inch maximum to start with but when air was being bled out it then moved more and seemed to free up a bit. At one point the clutch pedal stuck down and I pushed the fork manually into the cylinder after which it seemed to free up. Overall the amount it moves varies but I was suprised at how little distance I could make it move from underneath the car - about an inch and a half to two inches maximum from stop to stop - is this normal or should it be more?
Martin

Just went through this myself,I believe your problem is in the throwout bearing/pressure plate. On my 70 the cylinder which passes through the middle of the pressure plate broke up. The triangular shaped face on which the throwout bearing presses seperated from the crimped on portion which rides on the clutch fingers on the opposite side of the pressure plate.

The throwout bearing itself was in nearly new condition, the pressure plate showed evidence of heating. I don't know if that was the cause of the mechanical failure or the result.

Similar to you, I first tried replacing the slave and master cylinder. No luck. (By the way the non OEM appearing Victoria British master clutch cylinder was junk, and I had to replace it a second time.) I fear its time to pull the engine. Took about 4 late evening sessions. IF you can, degrease the engine and trans before beginning work. The oil covered state of the engine and trans was the worst thing about the job. (no the clutch friction plate was good as new.)

SM
stevem

Martin,

I had a similar problem a few months back. I also changed the slave cylinder no improvement. I bought a rebuild kit from MOSS and pulled the master cylinder. When I took the master cylinder apart the inside rubber came apart. Rebuilt the master cylinder and all is fine. Your problem maybe more severe but I would try this before pulling the engine.

George
G.L. Logan

Thanks for your assistance guys - unless someone comes up with a definative answer I think I'll start with the master cylinder before looking at taking the engine out. Looks like I'll be buying a seal kit this weekend!
Cheers
Martin

Before you go and yank the engine & trans out of the car...try this test:

1) Undo the rubber piston boot from the slave cylinder.
Unmount the clutch slave cylinder from the transmission bellhousing.

Attach a "C" clamp to hold the piston in the bore. Do not squash the piston
at the bottom of the bore with the "C" clamp as it will damage the piston seal.

Be sure that you do not let the slave cylinder hang by the hose.
Rest it's weight on a scrap block of wood, etc.

2) Get in the car and press down on the clutch pedal with your foot - and hold it there.

- If the pedal slowly drifts down to the floor - and there are no leaks at the slave cylinder - then
the master cylinder is at fault.

- If the pedal feels soft and "mushy" - but does not slowly drift to the floor - then there's air in the
system and it needs to be bled out.

- If the pedal pushes down a fraction of an inch, then stops (no drifting) - and feels rock hard -
then there's good news, and bad news. Good news: There's nothing wrong with the hydraulics.
Bad news: Your problem lays elsewhere - inside the bellhousing. (...but I have my doubts
on this last, worse-case senario).
Daniel Wong

This thread was discussed on 24/04/2003

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