Why are my front breaks locking up

Chase6214

Ok guy so I've pretty much replaced all the components of my break system with no change. Brake booster MC hubs calipers ext.. the break pedal gets hard and they lock up after driving a little. I crack a line to release the pressure and I'm good to go for a few mins anyone have any suggestions ive pit out too much money a

imidazol97

How old is the vehicle?

I'd suspect either a problem in the master cylinder or the brake lines. You have replaced the master cylinder, so we can assume for now that it's working as intended.

I suggest taking off the rubber brake line at both ends to see if it's allowing the fluid to return from the brake calipers. The lines can swell closed inside. The high pressure of the fluid when the pedal is depressed forces the fluid through the obstructed line into the caliper, but the caliper doesn't have the ability to generate pressure to force a little fluid back through the line to relax the caliper. The caliper stays activated rubbing the pads against the rotor.

The fact that opening the brake line AT the caliper allows things to work temporarily supports that theory.

One person found the line was so swollen that he couldn't blow through it. But the high pressure fluid can be forced through from the MC to the caliper.

Mr_Shiftright

Some people prefer to install braided stainless steel flex hoses, especially on older or higher performance vehicles. Definitely check for swelling, especially if someone is pushing on the pedal while you watch.

Seems like you've eliminated the brake booster possibility but perhaps the push rod in the booster needs to be adjusted properly.

Did you lubricate the brake caliper guide pins?