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

PaulHunt73 paulhunt73 at virginmedia.com
Tue Nov 8 01:52:21 MST 2016

"pedal goes almost to the floor with no resistance but enough to still work"

Expand?  If the biting point is very low when this happens, then either the pressure seal is not sealing when it should be, or there is air in the system.  If the biting point remains 'normal' then it's a purely mechanical issue, possibly pivots binding with heat expansion.

If the banjo union at the master is wet then that does imply a leak, which may or may not let in air, and further tightening may not seal it.  Also if it's wet it implies fluid loss, which should eventually become visible from the level in the master.  But that may take some time, and it will be affected by fluid expansion and contraction with heat/cool cycles.

If there is air getting in, then I can see that this becomes apparent on flooring the pedal, which will tend to push the air down while compressing it.  But it will float to the top of the pipe while the pedal is down, then when the pedal is released it will be flushed out of the system into the reservoir.  That is one of the many techniques that may be needed to get full travel of the clutch slave after working on the hydraulics.  The effects of incomplete bleeding i.e. air remaining in the system would normally be apparent on every pedal operation.

However that begs the question of how the air is getting in in the first place.  The fluid is either under no pressure at all (pedal released), or under pressure (anywhere beyond where the master piston seal closes off the bypass hole to the reservoir).  If air was getting with the pedal released then it would be apparent on the first operation no matter what the temperature was, and more than once on each drive.  And the pressure while the pedal was anywhere in its disengagement portion should stop air getting in, even on the upwards stroke, as it is the cover plate that is pushing back on the slave piston and hence the fluid, which is the main factor in returning the master piston and hence the pedal.

The other possibility is that something is causing the slave piston to be pushed back into the cylinder while you are driving, pushing fluid that should normally be in the system back into the reservoir, and creating lost-motion at the release arm.  This has to be taken up before you can start to disengage the clutch, so reducing pedal back-pressure and lowering the biting point.

But I can't really see how that could suddenly start happening with the new master, so the new master (subject to getting a proper seal on the banjo) has to be the prime suspect.


----- Original Message ----- 
  ... Now I have a new problem - pedal motion is perfect until the car warms up and then most of the pedal resistance is lost briefly...
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