Brake pistons won't retract

[fasteddie313]

Front right brake was hanging up so I went to exercise the piston..
Piston won't press in no way..
Pushed piston far out with brake pedal, still won't press in..
Cracked bleeder and piston pushed in..

Is their a reason this piston won't push in like normal brakes and just push the fluid back to the res? 

All back together and it works good now I think.. But curious..

[Oz]

If you check your other side pistons, you'll see they don't press in either. On cars, I have to use a C clamp to do it and it's impossible without cracking the bleeder valve.  Consider how much pressure is needed to press them against the brake pads in order to stop all that weight moving at speed!

You definitely have a problem if that side hangs up.  A dangerous one.  Either the pressure relief valve isn't working or you need to rebuild the caliper.

[Elandan2]

Another possibility is the the rubber flex line to the caliper has separated inside and won't allow the brake fluid to return to the master cylinder.

[fasteddie313]

Yeah, I figure it should just return to the master reservoir like normal hydraulic brakes do but don't know if their is something weird about these master cylinders..

I'm pretty sure the piston was just sticking in the caliper or possibly where the caliper slides in its bracket was sticking.. But I got the piston moving and cleaned and greased the slider surfaces.. Piston didn't look rusty or anything under the boot..
Rubber line looks good from the outside, will see if it hangs up again...
It was just dragging a bit.. Not uncommon..

[fasteddie313]

Pressure relief valve?

You mean the port in the master that opens when the pedal is all the way out to let the lines equalize with the reservoir?
Maybe my brake pedal push rod is adjusted improperly?

It should push back through the master and into the res right?

[Oz]

Yes, it should.  But if not working properly, it should affect all your brakes, not just one, so scratch that thought.   I must be limited to that wheel only.