Brakes

I have been through 4 master cylinders and finally believe I have the correct one. I can get brake fluid consistently to the front and when the bleeder screw is cracked the pedal drops. When I loosen the back the pedal doesn’t drop and air is always in the lines no matter how much we bleed it. There is no brake fluid leaks at all. We took it for a drive to work some air out and the pedal goes to the floor but still works. When we were done driving it the rear brakes were hot so they activated a little but not much. I was thinking it was a pushrod in the vacuum booster to master cylinder but it wasnt. I cant bleed these stupid brakes. I just checked and the parts store gave me a wheel cylinder for 11 by 2 inch brakes when I have 11.25 by 2.75 brakes. Could this be causing all of our problems or what is the problem?

That could be the problem but if you can’t get fluid to the back brakes the proportioning valve is tripped. Just replace it anyways. Old truck.

You can thank me later. Having the correct parts is on you.

Grit dog said:

That could be the problem but if you can’t get fluid to the back brakes the proportioning valve is tripped. Just replace it anyways. Old truck.

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Agree with the possible diagnosis. Question replacing the valve unless it has some other obvious issue. Read several posts about new PV's leaking or just plain failing. One failure was on a TV series, leaked. Most of the valves are offshore production.

Yeah keep your original proportioning valve. Or source a good used factory one if it comes to that.

the pv tool that centers the pv while bleeding helps. I went thru 1 new chinese prop valve then spent a little more on a 2nd one and it didnt leak

Ken B said:

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I got to change mine out a week AFTER installing the rad and fan shroud, but the new inner fenders were not installed yet. I didn't know my old body could still bend like that.

Ken B said:

the pv tool that centers the pv while bleeding helps. I went thru 1 new chinese prop valve then spent a little more on a 2nd one and it didnt leak

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What brand was the good one? I'm gonna need one soon for rear discs

Rustisbest said:

What brand was the good one? I'm gonna need one soon for rear discs

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Get NOS,or junkyard Cadillac Seville or Olds Toronoado

Ricko1966 said:

Get NOS,or junkyard Cadillac Seville or Olds Toronoado

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Junkyards vehicles around here are in a grown up fields and mudholes sitting on the ground with no wheels. One even has a couple guard donkeys lol. Not worth the hassle anymore.

Ken B said:

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Ooooooh. SHINY!

I had luck with summit brand proportioning valves. Work as expected and no leaks.