88' f350 diesel brake issue

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Active member
Nov 25, 2012
I'm along for the trip, not the destination.
my brakes on my 88' f350 7.3l dsl are crap. pedal is solid until you start engine then it drops to floor. i have been dealing with it for 4 months and there is ZERO fluid loss

here is what we have changed:
master cylinder, vaccum booster, calipers, pads, rotors, wheel cylinders, shoes, ALL lines(except from master to proportional valve and distro block), ALL hoses, proportional valve,anti lock brake fuse.

we have blead OVER 5 bottles starting from the furthest working to the closest, bench blead the master and bled the proportional valve.

Vaccum pump is supplying 27" of vaccum and the one-way valve is working properly.

I got that vaccum reading while ideling in park, should i take readings while driving?

anyone know how the proportional valve works/ the wiring of it or if it works off a certain fuse?
A master cylinder for a 1988 will definetly be a rebuilt. I would be trying another master. Mistakes happen in rebuilding shops like anywhere else. Iv'e installed bad thermostats, bad waterpumps and bad power steering pumps. I would buy from the same place as the warrantee is probably up on the first one. If that solves it repack first one in new packaging with the new receipt and get your money back. If I,m wrong my appologies in advance. Good luck.
had bought two different rebuilts from different companies same thing. after four months, changing everything, pulling our hair out we brought it to a shop. @#$%!. they rebuilt the master themselves, reset the proportioning valve and did some odds and ends and the brakes are fine, bummer.

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