Technical F-100 brakes

I have worked on my neighbors '68 F-100 brakes. It would pump the pedal up while driving to the point he had to get out, and crack the lines loose at the master cylinder, to release the brakes.

I replaced the master (it has no pressure valves in it) I replaced all the brakes, wheel cylinders, all new springs & hold downs. I took the proportioning valve out, and cleaned it. It is basically only a equalizer for the warning light, you can see through it, there is no valves inside. I flushed the lines, and refilled it with new brake fluid.

We were driving it the other day and it started to shake the front of the truck when he would use the brakes. I took the wheels off and knew I'd see fluid on the shoes, but it was clean, found nothing wrong. I checked the master for valves, I'd thought one was stuck, but there is no valves in it. So I took the proportioning valve out, to see if something in it was stuck, but there is nothing inside it to stick.

He came over with it tonight, with the drivers side wheel hot, and pulling to the left. I jacked it up and the wheel was tight to turn. I cracked the fittings at the master, and some trickled out of the rear (front brakes), and nothing came out the other.

I am lost as what it could be, anyone have any ideas as what could be the problem???
This why I changed everything in the first place, I thought it had a bad master on it.


Pat

 

I'm more inclined to say it's a bad hose from the frame to wheel cylinder, failing internally and acting like a check valve. Just because it looks "OK" on the outside doesn't mean anything and it wasn't on your list of replacement parts.

 

X2 on the hoses

 

Yep ive had hoses that did the same thing.

 

Yep. Check hoses. I had a 71 F100. It had a hard pull to the left after a brake job. New everything. Master and wheel cylinders. New shoes, hardware and hoses. Ended up being a bad new hose. It had a piece of material in the hose sidewall that delaminated and acted like a flapper valve.

 

Thanks for the replies!
I had to look, and see if I did put new hoses on it last night! This is one of his 4 trucks, I have been rebuilding, and replacing all the brake parts on. It turns out, I didn't put new hoses on this one, because he had them replaced a year, or so ago. I will be replacing them now!

Thanks, again. Pat

 

Also verify the rod from the brake pedal that contacts the master cylinder piston has some clearance when you let off on the pedal. If the MC piston can not fully return to its original position after the brakes are actuated it can cause residual pressure to remain in the lines.

 

Do you need another input for hoses?
Here it is

 

I went and put new hoses on it today. It turns out that I did just put new hoses on it. I thought I did. He will drive it around and tell me how they are. It took a few days to show up last time. This is one of four of his trucks that I did a complete brake job on. He buys all new parts, ms, wheel cyl, calipers, hoses, springs everything. Two got all new hard lines also.

He just bought everything including hard lines, for his '77 F100 stepside I'm doing also. I have one more to do after that also. He has 7 trucks! He gave a '95 Z71 I rebuilt to his one son, and is going to give the '77 Ford to his other son. I still have to put floor complete pans in it. I already put a new fuel tank, and fuel lines in, shocks, and then new bed floor boards in, after he gets it painted,

I had put a spring on the brake pedal on the '68, because it was leaving the brake lights on, after I did the brakes before, I know there is no pressure on the master.

Pat