Brakes lock up randomly on my truck. I thought it was rear.. replaced brake line with no luck. Today in the dark they locked up hard and when i got home i could see it was all 4 (glowing) locked up. Any ideas? Master cylinder?

 

Wow all 4 were locked up at the same time. I have never heard of that. I would speculate that is it something like the master cylinder? I dont completly understand how the hydro boost system works I wonder if it would have anything to do with it.

When you get a solution I am curious as to what it is. I have never heard of this problem before.

 

I have no idea what would cause that. My guess is master cylinder, but why???I wonder if there might not be moisture in the brake lines and it froze?? Might be time for a complete flush of the fluid. If you need a hand, call me. I'll be around in the morning(Sunday).

 

Were you on the brakes when they locked up or did it do it on its own?

 

It is really random. Sometimes no problem, sometimes it is locked up and i can bearly hit 40mph! Seems like when i push the pedal the brakes just don't release... something is holding the pressure in the calipers. I'll let you know Mike... thanks!

 

Any other ideas?

 

How is your brake pedal assembly? Does everything move freely under the dash? Just wondering if something could be in a bind mechanically under there? Do your brake lights stay on when this happens? If not, then maybe the pedal is returning all the way and it's something hydro?

 

I dont think this is a pedal issue. Brake lights do not stay on and the pedal returns to normal position, when I go to press it down it takes a small amount before i hit pressure.

 

Well I bled the front brakes out. Filled the miti-vac container full for each side on the front. Can't get it to do it now. It did however lock up tonight while going to the shop.... so i'm thinking its not a cold thing. I'll let you know what happens.

 

Had that happen this year on the wifes car. Replaced the mastercycender and brake fuild and all is well. Someone added the wrong brake fuild and it locked the front tires completely. Let it set and they released but did it again. I also changed pads and rotors but not cali[ers works fine good luck.

 

Did you put any diffent kind of brake fluid in it? You can use Dot 3/4 but not Dot 5. The difference between Dot 3 and 4 is the boiling temps. They are both a synthetic fluid. Dot 5 is a silicon and does not absorbe moisture. If you were to add 5 into your system your lines will swell and cause this, then you gotta replace your entire line system on your truck. I hope its not a booster issue cuz that can get expensive. Good luck and keep us posted on what you find out please.

Dan