front brakes lock

[nibbes123]

Need some help on this matter, the front brakes lock up when warmed up from stopping serve l times and unlock when they cool off. Replaced pads front and rear ,new rotors front and rear, replaced the master cylinder, new rear brake regulator bleed the system well. Looking at replacing the front flex hoses and rebuilding the calipers up front.
Nick

[So Cal Mark]

once they lock, try loosening the master cylinder mounting bolts a couple of turns. If the master cyl push rod is misadjusted, the brakes will release. Collapsed hoses can cause them to lock, but so can calipers if the pistons are seized

[nibbes123]

Will try it tomorrow and let you know.
Thanks

[nibbes123]

Hey Mark took off M/C and checked the booster rod depth and was good. Took off the rubber cover on the end of the M/C, installed on the booster, bled system and seems ok . Will try car on road tomorrow. Oh one more thing I rebuilt the calipers and changed the flex hoses so everything in the brake system is new.
Nick

[majicwrench]

Measurements are nice,,,,,,but next time brakes are LOCKED, like Mark said, back off MC and see what happens.
Keith

[jon8christine]

So I'm having the same problem. Car has been running fine for the past couple years. Haven't touched the brake system. On this trip I drove about 10 miles and after pulling in to a parking spot the fronts were locked up (assuming just the fronts as the front wheels were very hot and the rears we're fine. I had my wife bring me tools and after bleeding the fronts I was able to drive it home using the ebrake. I figured it was the master cylinder, and they're cheap, so I changed it. Drove around the block and was fine, but on a longer drive they locked up again.

What did you ever figure out?

[jon8christine]

Found a broken wire leading to the proportioning valve or whatever it is up by the master cylinder. Repaired it and thought it was fixed as it's been running fine for a week or so. Then today the brake pedal got hard and both front brakes locked up again. Tried loosening the master cylinder like Mark suggested and wiggled it around, but it didn't help. Bled both front calipers and it released and drove it home.

When I look on Vics website I can't find a matching proportioning valve or whatever it is that the lines run into up front. They just have the rear balancing valve. Could that be the culprit?

https://drive.google.com/file/d/1-KPX9d ... p=drivesdk

Not sure how to add a photo.

Any thoughts?

[Zoofly]

I'm having the same problem. I'm in the middle of swapping out the front calipers to new ones. I also want to replace the brake hoses but I'm having trouble getting the flare nut loose. I've heard a collapsed hose will cause the brakes to lock.

[jon8christine]

Yeah I've read that too. Both my front hoses are new a few years ago and the rears look OK. Going to try to shim out the master cylinder and see if that helps because if the push rod is sticking in too far it won't let the master bypass the pressure built up from heat. It's just weird that it would all of the sudden start that...

[jon8christine]

Shimmed the new master cylinder off the brake booster and that seems to have fixed it. One ambitious day I may adjust the booster push rod and take the shims out.