Drives for a while then brake pedal gets hard?

This happens when the brake booster push rod is adjusted out too far which does no allow the brake master to return fully holding the brakes on . To confirm the issue loosen the brake master mounting bolts 3 turns to see if the car starts to roll again, if so remove the master and adjust the booster push rod inward. Also a brake flex hose can come apart internally causing a short of check valve in the system but this is usually isolated to one brake either front or rear.

It seems to be both wheels so I adjusted the push rod inward that did the trick thank you.

My 1994 Chev 1500 2wd w/305 & auto has a bad brake problem. The right front brake locks up and won't release. It has a light drag when you drive it. It has burned up the brake on that corner. It gets so hot that the wheel has discolored and the plastic hubcap melted enough to loosen. I just replaced the rotors, calipers, pads, bearings and seals on both sides. Bled the system with fresh fluid. Everything looks perfect. IT IS STILL HANGING UP! I just drove it down the street after replacing the entire front brake system and it is smoking the right front pad just like it did before. The left front works perfectly. I have been repairing brakes for forty years on all kind of vehicles and have never seen anything like this before. What do you think the problem is ????
My cell no. is 540-907-8165 if you need to ask me anything. Please help asap. I need the truck tomorrow to get to work!

First, crack the lines at the master cylinder to see if the caliper releases. If it does, suspect fluid contamination causing the lip seals in the master cylinder to swell, trapping the fluid. If that doesn't work, open the RF bleeder screw. If it releases there, look at the rubber hose. See if you can crack the connection open between the steel line and the hose. If that does not let the caliper release, the hose is constricted. That is more common on Chrysler products that use a metal anchor bracket crimped around the center of the hose. Rust builds up inside the crimp squeezing the hose. I've had people tell me that can happen to any hose at the connectors, but there is a barbed tube inside the hose so that seems unlikey.

caradiodoc

I have an 87' Chevy P30 Step van, 350 Auto, The front brakes keep sticking/building pressured. I have to crack/open the bleeders on the front to release the pressure every 10-15 miles (depending on how many times I press the brakes). It has new: master cylinder, metering block, flex lines, calipers, pads, rotors, rear pads, repaired line in the rear. The only original stuff is the hard line from the master cylinder to the front & rear block.... I'm afraid I'm going to ruin the rotors.. they have already been " cherry red" at least twice. I've taken it back to the shop that put all this stuff on 3 times... they changed the metering block on the second time, changed the master cylinder (again) on the third time... I just drove it home and it did it again

Multple part replacement can throw a few wrenches into things. But I would do this:

Thanks for your response... but I have a question, how does this affect the front brakes building up pressure?

The height sensitive proportioning valve provides ideal brake balance according to weight at rear axle.

There doesn't seem to be a balance rather a large difference between the front and rear. The imbalance may be diverting pressure to the fronts.

The proportioning section of the valve proportions outlet pressure to the rear brakes after a certain rear input pressure has been reached, preventing rear wheel lock-up. Instead you are having front wheel lock up. Where the lines run into the correct ports on the valve?

I apparently don't have this "Height Sensing Device". I've crawled under it and there is nothing. Still not sure why it keeps sticking?

It's part of the metering valve.

Are any of the metal lines run close to the exhaust. Possible boiling brake fluid? I assume the brake fluid is fresh.

Since there is a relationship to how many times the pedal is applied, If you were to pump the pedal before it is started, will the caliper then stick or create pressure that is not releasing?

Another thing I would check is movement of the pads in the bracket. Pull a caliper and see if the pads are free.
IF they are too tight, this could happen. I assume a quality brake lube was used.

My right front caliper froze up and burnt the brakes. i replaced all the front brake parts with new not rebuilt. the problem came back after a week. i than replaced the proportioning valve with a rebuilt one. bleed the system and both front brakes are locked up after applying the pedal, and the brake light is on. help please

This problem is a classic brake flex hose falling apart on the inside. I would replace both to be safe here is a video and a guide to help you get the job done.

https://youtu.be/xMS8Xy4Xz1U

Please let us know what happens so it will help others.

Cheers

That worked perfect, you guys are the best I love this site.

When driving this truck some times the front brakes will lock up, the brake pedal is real hard to push when this happens. If i let the truck sit for awhile it will unlock and go like normal. This doesn't happen all the time.

Need some information. Is it locking up the fronts or the rears. Also is it disc brakes in the front. Drum brakes in the rear. Most common problem is the caliper piston over extending due to low pads or thin rotors

It's the fronts only and they are disc brakes. Thought maybe it has something to do with the hydra booster, since it happens when not even applying the brakes

It is possiable but unlikely that it is the hydroboost, because it requires mechanical force to activate. I would first pull the front wheels and check for caliper bind. A telltale sign of failure would be caliper being a redish color indicating it sticking and overheating. Also check the thickness of rotors and pads.

After about 20 minutes of driving my front brakes seem to be locking up on me. If left alone for about an hour to cool they are fine again.

My calipers are new and are not siezed. My flex lines are new and not collapsed.

This happen everytime like clockwork. As soon as the truck heats up after about 20 minutes of driving, I start to loose forward momentum and my brake pedal feels as hard as a rock.

Any ideas would be helpful. At this point I think I may buy a rebuilt master cylinder.

IF the fluid hasn't been flushed, I would recomend that as it may be boiling at the calipers.

You can plug the lines at the mastercylinder to check it. When plugged the pedal should be rock hard.

Well, I took off the Master Cylinder and that was in fact it. The primary piston could hardly be pushed in and it took a long time for it to return to its normal position.

Thanks for the help! =]