1996 Blazer LS 4x4, just had the front rotors pads and rear pads done 6 months back, the wrench who did it said the proportioning valve was locked up or something along those lines, and it wasn't pumping fluid to the rears(as well as a desperate need for pads and rotors)

All was well until today a few miles down the road the pedal became very stiff and the brakes would slowly release upon releasing the pedal, if you pressed the pedal before the brakes disengaged fully they would be very stiff, barely stopping or doing anything. Soon after the service engine light lit up and the brakes had a cooked pad/fluid sort of smell, the entire master cylinder was very hot, and it had plenty of very black brake fluid, no leaks of any sort. I suspected the master cylinder, and bought a remanufactured one for $50 bench bled and installed it, bled all 4 lines until fluid poured out. But the brakes still wont release quickly and barely stop and I don't feel much rear brake.

Help is appreciated

 

If the proportioning valve is messed up, replace it. It should be cheap to replace. Other than that the rear calipers might be frozen if you have a disk brake rear. I thought the 97 and older had drum brakes. In that case the wheel cylinders are probably froze up.

 

Drum on the rear.
How could i check the proportioning valve?

 

Not sure how to check it. I'd guess it's less than $20 for a new one though.

 

Little confused. If you Bleed all four corners and you got fluid to pass through the calipers and the Wheel cylinders then why would you suspect you have a Proportioning Valve issue.

Also, I have never heard of a Master Cyliner getting Hot. that's odd. I cannot see how a plunger of fluid would get hot.
I'm really interested in the outcome.

 

If a caliper or wheel cylinder is locked up and dragging causing heat it will cause the brake fluid to boil, all the way back to the master cylinder if driven long enough.

 

Im not sure on the proportioning valve, i was just trying to find possibilities.
The master cylinder was cooked! I found it odd as well, especially considering it was only driven about 8 miles(both ways, maybe 30mins to cool in between) when this happened.

Booster pump is good, checked that already.
I was wondering if this could be a stuck piston somewhere?

 

Alright, i checked some things out today. The brakes are still very stiff, even more stiff then when the brakes work properly and stop only at low speeds.

I have ruled out the proportioning valve. Theres is definitely some air left in the line i need to get out. I tried cracking the two nipples where 4 lines return to that large square block in front of the proportioning valve, but nothing came out.
Gotta be clogged returns. How might i flush them? Or i must replace the blocked lines?

 

Im also suspecting a blocked booster pump check valve, i couldn't get a good vacuum off it, but the line is clear on the intake side.

 

A wrench told me it was a blocked EGR valve.
It stops fine now, however the master cylinder still gets very hot, and i get a much stiffer brake feel in reverse for some reason. And within 10 minutes of driving the service engine soon light always comes on(but never at startup, only once the truck is warm)

Still scratching my head a bit. any help/explanation is appreciated.