What is happening is this: The brakes are not fully released. The more you drive, the hotter they get which causes expansion of the brake fluid in the caliper. That makes the pads tighter. As it cools, slowly the caliper releases.
Since this is a1972, it's possible this is a kit to change drum brakes to disc. So, if you know if that is the case, let me know.
First, I need you to check something. If the master cylinder was replaced, they may have incorrectly installed the pushrod causing a small amount of pressure to remain on the plunger. This could cause a slight drag that turns into what you experience. Check under the dash and make sure nothing is preventing the brake pedal from fully returning and make sure the brake light switch doesn't stop it from returning.
If that checks good, I want you to do the following. While the brakes are locked, loosen (not remove) the two bolts holding the brake master cylinder to the brake booster so the MC can move about 1/2" forward away from the booster. Does that allow them to release? If not, move to the next test.
Although the calipers were replaced, there could be a problem with the rubber brake hoses to the caliper. So, when they are locked, very carefully (so you don't get burned) slightly open the bleeder on one of the calipers to see if the brake releases.
Try these things and let me know what you find. Also, if you could take a couple of pictures of the brake master cylinder and the calipers so I can see what I'm dealing with, it would help.
Let me know.
Tuesday, December 28th, 2021 AT 7:31 PM