Sticking Master Cylinder

[ajluch1]

I rebuilt my master cylinder by putting in new cup seals.
After it sits for a half hour or more, the pistons freeze up. It takes a lot of brake pedal force
to unstick the pistons.
What's going on? Did I do something wrong? (I didnt use any kind of assembly lube or
anything. I just lubed the cups with brake fluid and reinstalled). Is their anything I can do to
fix this problem? Thanks for the help!

[Greg]

How old are the seals and was the internal bore of the master cylinder unmarked and almost mirror smooth?  If you pressure bled the system it’s possible to blow one of the seals over backwards, you would need to dis-assemble to check this.  That normally causes the brakes to go on but not release though.
Greg.