1989 Ford F350 Can't get hard pedal on brakes

1989 FORD F-350
88,000 MILES • V8 • 4WD • MANUAL
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GVRANCHES
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I can't get the brakes to bleed properly. I've replaced the brake booster, master cylinder (new-not rebuilt), vacuum pump(it's a 7.3 diesal), both rear wheell seals, several sections of tubing (due to rust) and a rubber hydraulic hose at one front wheel. The proportioning valve is bypassed by manual gizzmo that controls the amount of fluid going to the rear brakes.

I tried to isolate the front from the rears by plugging the rear oriface at the master brake cyl. This produced a harder pedal but I still couldn't get the wheels to lock up.

I had the vacuum pump and rear wheel cylyinders & bypass gizzmo intalled by two different shops. I'm stumped. Any suggestions will greatly be appreciated. You might want to know this vehicle came from the north and is very rusty. It has low mileage and steers good but sat up a good part of the time because it was used as a snow plow (4WD)

Thanks!
George V

I
Sep 9, 2008 at 5:06 PM
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BLACKOP555
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what seems to be the problem?

do you have any breaking?

incredible low pedal?

pressure build up with engine off?
Sep 9, 2008 at 7:12 PM
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GVRANCHES
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I have some brakes but unsafe to run on the road.
Brakes go clear to floor. when bleeding, air blasts out right rear (longest line); after a few procedures, it runs clear. Did all four four wheels in proper sequence and even bleed the master cyl by loosening connections. Pressure seems less with engine running.

I'm totaly baffled. Could it be sucking air somewhere ? I checked the entire system for leaks.
Sep 9, 2008 at 8:15 PM
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BLACKOP555
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do they keep getting more air in the lines? imeditely after bleading is done? or is fluid coming out with no air, just no pedal?
Sep 12, 2008 at 5:22 PM
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GVRANCHES
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Yes, air seems to be creeping back especially the right rear (the longest line). I would bleed them 4-5 times til finally no air, then go around to the remaining 3 wheels only to go back again to the right rear and find air again. I would have my buddy stand on the pedal, trying to bust out a line if he could to find the possibilty of a small leak somewhere--no find.

Another bit of info--I mentioned earlier the proportioning valve was by-passed with a manual valve. This was done at a brake shop, but the tech did not disconnect the wires going to the proportioning valve. I was hopoeful after disconnecting the wire would solve my problem but didnot.

I also saw on a Ford forum website where someone described my problem to a t, saying it was solved by "cross bleeding" but didnot describe how that was done. Another individual said the hydraulic hose at the fron wheel from frame to claipier deteriotes somehow to form an internal flapper vlave. He said after changing the hose, it solved the problem. I changed one hose but didn't change the passenger side yet. I appreciate any suggestions you might have. Thanks!
Sep 12, 2008 at 9:28 PM
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BLACKOP555
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what i would suggest doing would be quite simply to bench bleed the master cylinder and reinstall, then bleed out the metering/combo valve them go to rear right and work in sequience bleeding each one and seeing how it works.

the flapper valve deteriated hose problem usually will let fluid in but wont let fluid back through it and will usually cause a dragging problem NOT a air geting in line problem.

reember just because no fluid is leaking on a caliper doesnt mean it cant suck air back in.
Sep 13, 2008 at 7:35 PM
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BLACKOP555
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try gavity bleeding also, just crack all bleeders and let her sit for 1 hour.
Sep 13, 2008 at 7:36 PM