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MG MGB Technical - clutch pedal resistance

hi all,
i keep losing the resistance to the clutch pedal when i drive. on startup the resistance is as soon as you push the pedal. after driving a short while the pedal does nothing about a third of the way down and clutch bites at bottom of travel.if i stop car and go back to it after about 10 mins all is good again. have changed the rubbers in the master which had a slight weep but still the same. no leak on slave. does it sound like the master cylinder needs replacing.
on the mgc
thanks bob.
bob taylor

Sounds like what happens when the relase ring on the diaphragm is wonky. It shimmies around and pushes the release bearing and clutch arm back so it requires more pedal stroke to make up the difference.
Measure the stroke at the slave cylinder pushrod while a heloful assistant operates the pedal. if 10-11mm, the problem is inside the bellhousing. Les than that indicates hyrdraulic side problem.
Paul Walbran

If mechanical problems are pushing the piston further back into the cylinder than it should be, then one long operation of the pedal should be followed immediately by normal operation, until such time over a period with no clutch operation that the release arm has pushed the piston back into the cylinder again.

If this is happening, then the release arm will have a certain amount of free play, normally there should be none.

The cylinder is supposed to contain a spring pushing against the seal and the piston. This should continually be taking up any free play in the mechanical parts from there on, by pushing the piston out. This could be why it is OK again leaving it a few minutes with the engine stopped.

Worn crankshaft thrust washers allowing the crank to move back and fore could be a factor - see if the distance between pulley and front cover is changing as the clutch is pushed in and out with the engine running.

could be that the light spring inside the slave cyl. has been missed out when the cylinder has been apart in the past or the spring has rusted and lost it's energy
If you push the clutch arm by hand so that the pushrod pushes the piston back into the cylinder then release it ,the spring should be plenty strong enough to push the piston back out to take up the clearance . If it doesn't return out there is a problem with the spring
If it does return out -follow Pauk W's advice
William Revit

slave corroded, cleaned up,new rubbers, all good,, thank god for that.
bob taylor

This thread was discussed on 05/08/2016

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