It all started when I pressed my brake and pedal went to floor, so i replaced the MC, then looked at the brake and saw the caliper was leaking lightly out around the Front passenger caliper pistons, so I bought a used caliper. installed it all and bled the system and bench bled the MC correctly. then the caliper siezed up while driving, so i bought a Brand NEW unused caliper and installed it with new hoses. New caliper siezed up!!! I tried pulling the fuse to the ABS too, nothing helps, brake builds up and stops the car. the only way to release the brake is to loosen the bleeder on the FR caliper, or wait for 10-20 minutes (with the car off). I have no idea what to do next. Any Advice!!!

 

Did you drain old brake fluid and put in all new? Is the brake fluid black (dirty) or clear (clean). You can use a turkey baster to suck out wht is in thge reservoir and open all the bleed valves and continue draining until it runs clear. If the fluid is badly contaminated, the particles in suspension are what makes it black instead of clear and this cam be the cause of it sticking.

Or the inside of your brake lines could be corroded if the brake fluid was never drained and replaced. What year? Miles?

Look at the brake lines, are they corroded?

Time for some detailed first hand inspection and investigation.

 

its a '98 with 140k on it. I flushed the entire system. Its all new brake fluid. even the old fluid was still pretty good looking. none of the hard lines look corroded.Is it possible the ABS has a valve or something locked up? It really makes no sense to me. When I pumped the brakes for bleeding, there is absolutely no hesitation for fluid to come out the bleeder valve. no lines look pinched. Im thinking about removing the ABS altogether and running all new lines. Is there a write up on this? other than the 2 simple diagrams, i havent seen one showing which ports on the proportioner valve need to be plugged to which hoses. Also, i removed the 2 fuses under the hood (ABS pump 40Amp fusible link, as well as the 30amp fuse) Are there any others?

 

Do these trucks have proportioning valves? Could that be bad and dumping all the pressure into one caliper?

 

proportioning valve would put pressure on both fronts im 99% sure

 

Hmmm. I would check the rubber hoses then for blocks. See if the issue is there. Idk. It'd be weird if a blockage let pressure into the caliper but not out.

 

replaced rubber hoses with brand new ones already. i thought maybe couldve been a collapsed line, didnt help.

 

Sorry Ive been out of the country. I bought a brake line plug and plugged the solid brake line for the pass side caliper, drove it around (just diagnosing, not a temp fix) It took a good bit longer, but sure enough the driver side seized up too, so it has got to be the prop valve. will be replacing tommorow.

 

Did you install an aftermarket master cylinder?

 

Replaced the prop valve, still have both front brakes building up pressure and locking down. i can open the bleeder valve on either left or right to release the pressure on both. So in total, i have replaced the MC, Prop valve, new caliper, pads and brakes hoses. Ive checked to make sure none of the hard lines are bent, pinched or anything, Ive also pulled the fuses to ABS, so the only other possibility i can see is a bad valve in the ABS pump thats stuck. any other thoughts anyone?

The MC is aftermarket, but did solve the mushy pedal problem, so i think it is working.