I have a friend that has a 98 , 12V 2500 extended cab 4X4, 5 spd. trans, w/ 60,000 miles. He has had the master cyl replaced (under warranty I think) a while back. He is experiencing severe rear brake lock up when stopping. He says that if he is in 4WD that it dosen't happen as much. Could he be having problems with his ABS? Or could the proportioning valve be bad. Any help on how to trouble shoot this problem would be appreciated.

Thanks, Frank.

 

He doesn't have a leaky axle seal does he?

 

He works at a mine and has strange hours. I will let him know to check this and will advise you of his findings.

Thanks, Frank

 

Might even be a leaking wheel cylinder too. Any contamination will cause problems. Does the ABS light come on like normal during start up? How much pressure does it take on the pedal? If the M/C was replaced under warranty, could it be possible to fix the rear brakes under warranty? Lots of questions and little answers..................
Tom

 

Sorry it took so long. Both wheel seals were leaking. Didn't seem like a lot of grease contamination on the linings but seals and linings were replaced. Seems to have cleared up the problem. It seems strange that grease contamination would cause this problem, I thought it would have been the opposite.

 

Yea, you'de think it would act like a lubricant. I wish I knew why it works the opposite too. Just nice to have the brakes bake to where they should be.
Tom

 

My theory on grease causing rear drum lockup - the gear oil or brake fluid causes the pad material to swell slightly, making it "stickier" and more "grabby" than when dry. The swelled material apparently has a higher coefficient of friction but can be "burned down" by the first couple of applications until it is back to being smooth agian.

My brother's '77 W200 always locked the right rear on the first stop each time you drove it after sitting overnight. Took a few months before the obvious signs of seal leakage began to show. Changed out the pads and seals and cleaned up every thing and it hasn't happened since.

 

What was odd, is that the linings looked glazed. There was some uneven wear on the top of the shoes on one side. It seemed that the adjusted was hard to turn and probably wasn't working on that side. The swelling sounds like that could be the cause. They must use different material in big trucks because all we used to do was steam them off and reuse them.

 

Zackly what he said. Seen it before. They can be cleaned and saved in a pinch but I replaced them both times.
This is also why I replace everything when I do a brake job. New calipers, wheel cylinders, hoses, and all.

 

i have the same prob going on! i changed driver side rear wheel cylinder last spring cause it was leaking thought it might have been a bad seal so i bought new seals but they where not the prob. but now im thinking they r cause i have the same prob with the rear brakes locking up!

how long does it take to put new seals in?