Vacuum leak or bad vacuum booster
Check to see if you are getting vacuum to it
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.
yes , you will have to get a master cylander that will match the calipers and system
have you tried the proportioning valve. sometimes dirt will get in there and clog the returns.
If calipers were also replaced there has to be something else preventing the pads from backing off. If it was only one side I'd suspect the hose, if it's both I'd have a look at the master cylinder.
Did you bench bleed the master cylinder? Check the front flexible brake lines - they may be internally rutured and are blowing up (like a balloon) when you step on the brake
Make sure calipers aren't frozen
check linkage down near the pedals..there might be some excess play that is causing the problem
could be the master cylinder. or the calipers may be siezed
At least the slave cylinder. The clutch master cylinder can be replaced at any time.
Master Brake cylinder replaced and lines bled-how long?
after the clutch master cylinder has been replaced.