[Mgs] [MG-MGB] Clutch problems with thermal component

PaulHunt73 paulhunt73 at virginmedia.com
Wed Nov 9 01:27:48 MST 2016

Firstly the tilt in the later clutch master - that was to clear the larger brake reservoir cap on North American models when they gained the dual circuit system, but was fitted to all MGBs.  AFAIK the tilt rotates the master cylinder about the centre-line of the bore, so everything should remain in line.  Whilst the pipe could be moved to mate up with the master outlet, if the position of the bore changed relative to the pedal that could cause problems.

1.  If you continue highway driving, after you have experienced the long travel and corrected it with a couple of pedal presses, does it happen again?  Or does it only happen once no matter how far you drive?  If it only ever happens once then it looks like a master seal problem.

2.  Another test, once you feel the slackness, stop the car where safe without using the clutch, and see if you have any free play in the release arm.  If there is, then something would appear to be nudging the piston back into the bore.  However, there should be a spring inside the cylinder which is constantly trying to push the piston out, and that should continually being taking up any free play.  The purpose of this is to take up any and all play from there on i.e. in the release bearing and friction plate, it is this that makes the MGB clutch self-adjusting for wear.

As another part of this test, at various temperatures, by pushing on the release arm move the push-rod and hence the piston all the way back into the cylinder, let it go, and it should ease its way out again.  Make sure the master reservoir has some space at the top to avoid the fluid overflowing.


  ----- Original Message ----- 
  It is a bizarre problem. I was hoping someone might have had similar problems. Since my last email, I have made two 15 mile drives with the same very predictable issue. The master remains the primary suspect because the issue happened after replacing the master cylinder. The slave cylinder was an aftermarket replacement I put in about 4-5 years ago but the only thing I have done with it is to drain the brake fluid.

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