It would be helpful to know:
What vehicle you are working on.
The condition of the rear brakes, and were they also bled.
Does the brake fluid level stay full, if no then there may be a brake fluid leak.
Air in system? Remove and bench bleed master cylinder Bleed lines and calipers
It's rare....because usually the master cylinder will allow pressure to bleed off. Not the other way around. But if you have replaced the calipers, this is the next thing I would check. I suppose it could be sticking.
I had one do this and I had to change the brake calipers. Problem was gone.
have you tried the proportioning valve. sometimes dirt will get in there and clog the returns.
Make sure calipers aren't frozen
could be the master cylinder. or the calipers may be siezed
Bleed the master cylinder.& then rebleed the system.
I am having the same problem. Ist time overhauled calipers. Right front pads wore out quickly. Next replaced calipers, same deal right front is locked to the point where care shakes and cannot be driven. Thinking proportioning valve or master cylinder? Anyone ever run into this?
Check the calipers. If the calipers pistons are extended to far - this could cause the brakes to lock up. The pistons cannot be retracted.
If You Replaced the master cylinder Did you Bleed it as well? if not you need to bleed it first. then bleed the brakes start with the passenger side rear, then driver side rear, then passenger side front, then finally the driver side front.
your brake system has air in it and needs bleeding. new calipers are a real hard to bleed
no