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MG MGB Technical - Clutch Phantom

My clutch (which has about 5K miles on it) Acts quite inconsistent. Today with temp about 60 degrees I took the car out and brought it up to temp and the clutch acted perfect doing everything that is expected. However I can get in the car tommorow and after a warm up she will slip in third and fourth if I want to get up to speed fast. I have replaced the slave /all rubber hoses and the pin and rod that goes into the slaveslave. I have seen in some thread forget were that when the engine heats up the fluid expands up the the master cylinder and causes the sensation I'm seeing.But I have replaced all concern parts. Is it possible there is still air in the salve line or in the slave that could be causing this??
Any help or thoughts appreciated.
Bob Jorglewich
Holbrook ny

" I have seen in some thread forget were that when the engine heats up the fluid expands up the the master cylinder and causes the sensation I'm seeing."

the only way this would happen is if the cap on the maser cylinder had a clogged vent hole. Have you checked that vent hole in the cap on your M/C? Cheers - Dave
David DuBois

thanks will check

Sounds like it could be oil from the engine or gearbox getting past the oilseal and on to the clutch plate.
Trevor Harvey

Air in the hydraulics causes the opposite problem - the clutch doesn't disengage enough and causes grinding, baulking and a low biting point.

If it is pressure building up in the hydraulic line the other symptom of this is a very high biting point. However you could get the same symptom from a mechanical problem that isn't taking all the pressure off the diaphragm springs. When you are experiencing the problem, slacken the slave bleed nipple and if you get a spurt of fluid and then the clutch is OK, it is hydraulic pressure that is the problem. If it makes no difference it is mechanical. Another cause of the hydraulic problem is if the master push-rod and piston isn't coming back as far as it should do, either because of a mechanical problem up by the pedal linkage or inside the master or incorrect parts i.e. an over-long push-rod. The latter is also easily detectable once the pedal cover is removed, as the push rod and clevis pin should be loose, i.e. a bit of free play as you start to move the pedal before the push-rod moves.

FWIW oil on the clutch plate in my experience has led to a very sharp clutch, i.e. either in or out, not slipping.
Paul Hunt


Almost afraid to ask if you have OD in your car since you are indicating problem occurs in 3rd and 4th gear. Any idea what kind of oil is in the trans?

Fred Wright

Fred I have not changed the tras oil since I have had the car , and haven't had to add. Plus no overdrive.

The clutch is more likely to slip in 4th (then 3rd) than 1st or 2nd.
Paul Hunt

Paul and others thanks for your help ,drove it this am was perfect but was not able to get it to normal run temp as the rain came. will try your advise Paul
thanks again]

Bob J

This thread was discussed between 06/04/2009 and 07/04/2009

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