PCV Bleed valve 5th gen issue.

[courtuk]

So after I reassembled (not rebuilt yet) the secondary master cylinder, I can no longer draw fluid through the PCV by vacuum pump... However if I pump the rear brake pedal then fluid will flow through the PCV valve, looking at the tube I attached, the fluid does NOT back flow even if I do not tighten the PCV bleed valve. It seems my secondary master cylinder has a one way flow, and a stiff one at that. Has anyone had a similar experience? I did take out the green cartridge in the SMC and cleaned it and replaced it back in the correct orientation. Very confused about this, not sure if this is meant to be a design feature to aid bleeding... or if I've broken something. Fluid can still force through the SMC to the rear bleed points via foot brake, just not via vacuum pump. Front centre bleed valves are both normal and can draw fluid. I did wrap the bleed nipple in PTFE tape to stop air bubbles sucked in ... so before when I was sucking air perhaps it was only coming from around the nipple thread.

 

Currently I'm stuck with a locking rear, due to brake overheating and fluid expansion. Wheel releases when cooled down. Trying to trace if it's the SMC or rear MC. Might just rebuild both for the fun of it.

[Terry]

If it frees up when the system cools down then I'd suggest the caliper is OK but you may have a blocked return port in either the master or secondary master. The return ports are pinhole sized and easy to clog. When you release lever pressure, these ports allow the brake fluid pressure to release in the caliper and lines. You can verify whether pressure build-up is the problem by selectively cracking the bleed nipples on the caliper to see which one releases the brake, that will tell you which circuit (outer piston = foot brake, centre piston = SMC) is trapping pressure.