I finally got the exhaust on my car and took it for a drive. After about 15 miles, the front brakes are getting hot. After it cools down, they're both free-ish, slight dragging. Leaving the lines on the master cylinder, I pulled it away from the master-vac. Then screwed the push rod in a ways. I also adjusted the clevis on the brake pedal a couple turns. Took it for another drive today, trying not to hit the brakes, after about 15 miles, got home, jacked the front of the car up, brake pads are tight against the rotors, both left and right. Ugh. Both the master cylinder and master-vac were rebuilt. I did put new pads after restoring the calipers. Whatever it is, it's affecting both left and right brakes equally on the front. When I found this car, it had a later master cylinder on it, with a long tip on the push rod. When I tried to bolt the older correct master cylinder on, it wouldn't fit, the push rod was too long. Fortunately, I had the master-vac that had the shorter push rod in it. I thought I measured everything right, and it bolted up. Anybody got any suggestions? I don't like spilling brake fluid on fresh paint! Why aren't those calipers retracting?

If the fluid can't flow back and there's any air in the system they will get tight when driven

So are you saying it could just be air in the system?

I believe that’s what he was referring to.

15 hours ago, Parman said:

Leaving the lines on the master cylinder, I pulled it away from the master-vac.

If you can do this when the brakes are stuck it will tell you if the rod from the booster to the MC is too long, causing the return port in the MC to be blocked. You'll have to do it while things are still warm though. Patcon is implying that the air expands as it gets warm creating pressure in the system.

They make a tool for setting the booster rod length. It's a fairly common problem, especially with rebuilt boosters.

If you stare at the parts long enough you can figure out other ways to get it right.

I appreciate all the info. I removed one of the calipers and to compress the pistons, I needed to use a C clamp. Is this normal? Seems like they're awful hard to move. It takes alot of pressure to get them to move one way or the other. So when a guy applies the brakes, then releases the brakes, there's no spring to make the pads retract, they just kinda ride along the rotor. This drag is causing things to heat up and expand, making it tight. Some Fords have springs in the calipers to make them retract.

I applied the brakes while the front end was lifted up, it wasn't heated up. After releasing the pedal, there was a more noticeable drag on the rotors. I pulled the master cylinder away from the master-vac, and there was no change. I don't think that's the issue.

Was the bleeder open when you tried to push the piston in?

The Nissan calipers use the rubber seal to retract the pistons.

One common cause of sticking caliper pistons is collapsed rubber hoses. The MC can generate high pressure to push through the collapse but the rubber seal cannot to allow the pressure to release. It becomes like a check valve. On some cars the cause is a metal clamp on the hose that rustjacks and pinches the hose. But just degrading internal material can cause it also. I ould guess that a kink in the hose could cause it also.

Edited 16 hours ago16 hr by Zed Head

No, I don't think so. But the line was disconnected.

It has new rubber hoses, so don't think that's it. The hole in the master cylinder, that creates the pressure when you hit the brakes, is this also the return hole for the fluid?

Edited 16 hours ago16 hr by Parman

But, don't overlook the brake pressure warning switch. Or the NP valve. Can't remember the car. (https://www.classiczcars.com/settings/signature/) It can get gummed up also.

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Probably worthwhile to read the Brake Chapter. It's not long. Well-illustrated.

Opening the bleeder when the brakes are stuck will tell you if the problem is pressure in the caliper or something else. If there's pressure in the caliper you can work your way back to the the MC fitting by fitting. Or work your way down, from the MC. First you need to know if it's hydraulic pressure or just mechanical sticking.

Edited 16 hours ago16 hr by Zed Head