Hi all, new to the forum.

I can usually figure things out by just narrowing down the common denominator, but this time I have been beating me head against a wall.
I have a 1977 F150 4X4 351M auto trans power brakes disc/drum. I have changed everything, except the prop valve, and the MC twice, one rebuild and one brand new. Not my first brake job. I have bleed the hell outta this thing... Problem is the pedal goes to the floor and only starts to grab at about 3/4 of the way down. They all lock up thats the strange part but only once the pedal is in the carpet.

I have adjusted the rod on the power booster, a lot of people seem to over look this from what I read on here. I have gone over everything except I saw on here a tread about the Proportioning Valve. There is a pin your supposed to pull or push depending on the model. Could this be the culprit? Does't seem like it but I am running out of things to check.

Thanks for any help

 

Please excuse the late reply....have you got it squared away?

If not, a coupla things to check: M/C has been bench bled, yes? Have you done a booster check? Any/all rubber lines replaced?

No air leaks when the brakes are farting? All connections tight and secure?

...And the rear shoes are adjusted properly and the primary shoe(s) facing forward, yes?.....new pads/shoes all around?

The Prop/Metering valve gets either pushed in or pulled out, depending on the vehicle's GAWR....it also can go only one way...if you have a brass one, it gets pushed in while a cast one gets pulled out. Yours I think gets pulled out. I haven't actually noticed a big difference if either one gets pushed or pulled whilst farting the brakes.

 

I'd check the pin first.

 

Thanks guys, still having the issue. I bled the lines again, no air, and yes bench bled the MC. I also tryed with the pin in and out on the PV, did not notice a difference either way. My rear brakes are adjusted good witha little drag and lock up when I slam on them but the fronts do not. I have done everything I possibly can to check the booster, and it checks out good.

I think my nest step will be to take the front calipers off one at a time and lightly step on the brake a fill them with fluid, the crack the bleeder valve and see if any more air comes out. If that is not it my last solution is to isolate the MC, step on the brake and see what happens, if good attach only the rear brakes, if good attach only the front brakes. If either is bad I know where to start...AGAIN....

 

Ok....be careful when you step on the brake with the calipers off...you don't want those pistons to go wazoo on ya....but then again, if they're original and not moving when the brake is depressed, they might need a good cleaning and the rubber 'O' ring replaced - a royal pain the kiester.

Let us know your results.