I can think of two possibilities:-
1. Could the operating rod be adjusted in too far?
If the travel of the pedal is reduced by too much by extending the adjustable rod, then the master cylinder piston will not return far enough to clear the relief port. The system will trap pressure if it heats up and the fluid expands with nowhere to go.
Try putting a little bit more slack in the travel of the pedal.
2. The other possibilty is corrosion in the master cylinder bore due to water in the fluid settling at the bottom of the system. I had to change the rear master cylinder on my 851 last month because the piston was seized in the bore and would not return. There was too much pitting to clean it up and change the seals.
Good luck!
Mike
Hybrid Mode
