I searched but couldn't really find what I'm looking for, and I'm confident the PO just slapped stuff together. I have drum brakes all the way around. I have a 2 pot MC feeding a proportioning valve going to the drums. The pedal rides obnoxiously high and the slightest touch of the pedal sends you through the windshield. I also noticed at times of extended braking it seems to lose power boost and goes manual. I'm curious to know what I can do, to tame this brake system down some and get the pedal closer to the floor.

 

It looks like you have brake fluid leaking where the master cylinder and booster meet; either the piston seal in the master cylinder is leaking (this will suck brake fluid into booster and damage booster diaphragm) or the M/C cover is leaking (a minor problem that is an irritant more than a problem). My guess is the booster/Master/proportioning valve set up is from a disc/drum system. I believe pressure is higher for disc brakes so u may be getting too much psi to front brakes creating the uncomfortable grab and close up windshield inspection u are experiencing.

 

All 1967 and later FoMoCo Passenger Cars, F100/350's, Bronco's and Econolines have a dual master cylinder and a Brake Pressure Differential Valve.

These two parts are specific to disc or drum brakes. Disc brakes became standard equipment in 1973 F100/250 2WD & F350, 1975 F150 2WD, 1976 F100/250 4WD

The P/B booster on the OP's truck is HUGE .. looks to be from a 500 and larger series truck, because it ain't from an F100/350 of any year.

 

I think tomorrow I'll try and take the booster, and proportioning valve out and see how it does. I grew up driving post WWII jeeps so my braking foot is conditioned for manual brakes.

 

You sure bout that Mr. Wilson? Without going out in the cold dark to look, it sure resembles the 76 booster on my truck.

I am going to say that it appears that some idiot started a power disc brake upgrade but never finished it. The porp valve is for disc brakes and might be causing concern.

When I did my upgrade I had to relocate the connect point under the dash to drop the pedal down where it should be.

J You do have a leak that needs to be taken care of.



John

 

The power drum boosters used on 1965/72 F100/250's could be either 6.75" or 8.94" in diameter.

1973/79 F100/250 power disc brake boosters could be 11.00" or 11.46" in diameter.

But the booster on the OP's truck looks to me...to be larger than 11.46."

 

[QUOTE=jowilker;15029412]You sure bout that Mr. Wilson? Without going out in the cold dark to look, it sure resembles the 76 booster on my truck.

Ditto; appears similar to booster I salvaged from a 76. More knowledgeable member can probly better advise, but it appears the prop valve may be original and the booster possibly a replacement, best to determine; may need to replace the booster for all drum, then clean and repair leak on prop valve? .

 

Bill, It is getting dark again but I did go out and look, my vac connector seems to be further down the side but surely resembles the photo in looks ands size.



John