We replaced the master cylinder , hydro boost and calipers , 2 break lines, pads and bleed the system. Thought things were fine. Had brakes. But when we drove it 2 miles the more you drive it the more they stick till they lock , when they cool they release.

2 things come to mind:

If the calipers are new and free they should not drag unless there is some internal pressure.

Perhaps the system (calipers?) may still have some air somewhere? As they drag and heat up, the air may be expanding?

Is the pedal linkage properly adjusted? If the brake master cylinder plunger is pushing into the cylinder at rest, the brakes will see pressure. (Like riding the brakes)

My problem was an old brake line. It would collapse, replaced it and problem went away.

Mine problem was the same as Mary Ray . Collapsed rubber brake line. Bob

I had this problem about 8 years ago with a front brake. At that time I replaced all the calipers and rubber lines and put a new master cylinder in. Monday when I took it for a test drive to check out the rebuilt Quadrajet, it started slowing and a guy next to me waved me over. The right rear was smoking and when I crawled under I could see fluid dripping from the caliper and the disk was HOT! I let it cool down and limped it back home with no further problems but when I backed in the driveway the brake light came on so I lost fluid through the burned out seal. I made an appointment to get the caliper replaced but I think I'll get some more opinions before I throw money at it without knowing the cause.

It's the rubber brake line between the frame mounted hard lines and the caliper. Ditch those and buy the braided stainless steel ones from Russell on line. Measure yours and get the same length. Recommend also to flush system and refill with DOT 5 synthetic. Much higher heat range and won't absorb water like DOT 3.

Mary, Bob & Tom, that's what I thought. Had it on an old Cadillac. Inner hose collapses and will not allow hyd pressure to release. I suppose the same could happen even if the rubber hoses were wrapped with metal braid.

Not the new stuff. It is one extruded, reinforced rubber tube, not a two piece, and the stainless braid is then pulled over the tube. The days of ply type hoses is long over.

Thank you all so much for the help and info. Have found a web site that may prove helpful http://www.brakeandfrontend.co...ower-assist-systems/

I had same problem with front brakes sticking . I jacked up front end, had wife apply brakes then release brake tried to rotate wheel, couldn't brakes were still locked. I cracked bleeder on the brakes released a little break fluid wheel turned very easy brake was released . The problem was the rubber brake line.

I have run into this bad brake hose problem a few times. Had this happen on my sons front brake of his MX bike. Intermittently locking his front brake and wheel up. Down he would go. He was wondering if he knew how to ride. Had the same thing on my V.W. bug rear brakes. Split the old lines and found the rubber almost fish scale looking acting like a 1 way valve.