MkIII Master Cylinder Gotcha

Hi Gang,

Just thought I'd share a solution to a problem that had me scratching my head.

Having overhauled my Front Brakes, including checking the caliper was freely moving and adding new pads and a Master Cylinder reseal I was having problems getting it to work right, bleeding was difficult and also the brake would bind and only slowly release after use.

I tried a few things, and found I could get it to release if I cracked open the bleed nipple, meaning that the problem was pressure retention. So I had the MC off again, dismantled and rebuilt, and carefully checked the return action of the piston. Then reattaching the lever I released the very simple answer,

I had been tightening the the lever pivot bolt too much, so that it was causing the housing to tighten on the lever, not much, but just enough to prevent it freeing off under the pressure of the return spring, therefore not releasing pressure

I like to think I'm usually on the ball, and believe me the I'm not one for over tightening things, .... So I thought I'd put this out there in case it helps someone else - Don't tighten that pivot nut much at all!

different levers will give the same result, they can place the piston in a different position.

And the pivot joint anointed with moly grease as well?

madass140 said:

different levers will give the same result, they can place the piston in a different position.

Click to expand...

Yes, I can believe, I now appreciate the -now obvious- importance of checking the piston can get back as far as the internal spring wants it.

concours said:

And the pivot joint anointed with moly grease as well?

Click to expand...

Yes and also rubber grease in the cylinder and on the piston to prevent corrosion and , well, lubricate.