Brakes were mushy when I bought it.
Installed rebuilt Master Cylinder - brakes still mushy.
Lived with it for a while. Then bought $6 bench bleed kit.
Bled MC on truck, and viola! Good pressure.
A couple of days later, drove truck, and mushy again. Stayed mushy.
Bought new MC.
Brakes are still mushy.
Frustrating.

Fronts grab, but not so good rears. Front pads, rotors, calipers are good. New shoes, wheel cylinders, and spring kit on rears. Adjusted rears out plenty far enough.

When I bleed the lines the fluid squirts out like it should. But brakes are mushy. Not right.

Weird. They don't fade. Doesn't help to pump them. Stay mushy with pedal going too far to floor. Not right and not good.

Your ideas will be greatly appreciated.

RB

 

have you replaced the rubber flex lines at the wheels? That would be my first step.

 

I'd flush ALL the old fluid out of the lines before trying more expensive measures.

 

I had trouble one time with the proportioning valve just below the MC on a 75 F250. Its been awhile back, but I thought there was a place to bleed it? Ended up I had to replace it (basically no rear brakes and it was grabby on the front like yours. It would act like it bound up and then all at once let go, like the valve was sticking). Solved my problem anyway? It might be worth checking? If your changing soft lines, don't forget the one that goes down to the rear axle. Could still be your MC too? Did you try bleeding it again?

 

Thanks for the suggestions. I'll check all of them when the weather clears up a bit. Then reply what happens. Thanks.

 

The snow is gone enough to start working on it again. I thoroughly bled all four wheels, and adjusted the rears out a bit more. Maybe I'm just wanting these brakes to be as good as the brakes on my '95 Dakota? And maybe I just need to accept the brakes on the Ford for how they are now? I have to say though that every time I do something the brakes improve. It stops and all that, but they're just not as solid as I think they should be. Next thing I'll check/replace the flex lines. And report back.

 

I also have a '77 F150 with mushy brakes. I'm interested in hearing your fixes, so Please post again, Elk Ears.
I know why mine are bad, for a start. I've kept up on the fronts, but let the rears go for a while now, since most of the stopping power is in the front. I'm in a mountainous area, though, so I'm going to do the whole works on the rear brakes again in the next few days. If mine stay mushy, I'm paying attention to this post. If I figure something out, I'll post it.
cheers

 

I made a self bleeder with a plastic jug and 1/4" tubing. And then gave each wheel cylinder 12 to 16 full pumps of the brake pedal. Kept refilling the reservoir. And adjusted the rears out to where they seemed a little too tight. All that helped them. Next thing that would help is a new or better booster. Adjusting the rears out helped probably the most, and I think I'll do that again. I installed new adjuster spoons on each side, but might need to get new star screws also, so they'll stay adjusted out.

They're still not where I'd like them to be, but I'm living with them.

 

35 year old braking system you got there.. The Rear brakes are probably not working right. Did you manually adjust them? If there adjusted then I'd replace the rubber line then the rear brake cylinders proportioning valve and rebuild the brake themselves. Ford had super sensitive brakes in the 70's. My Mach I has those brake. Every time I drive it I have to get used to how the brakes are so tight..

 

The rubber lines and proportioning valve are the only things I haven't replaced. I'll have some time to do that this summer. Thanks.

 

But it could also be that my booster is a little weak. Seems like I read somewhere about how to test it, but don't recall where or how.

 

I completely rebuilt rears down to the wheel cylinder. New drums, brakes, springs, cylinders. I then bled brakes at each wheel, (farthest first, of course) until fluid was clear. (good friend helped, while doing the newspaper crossword puzzle. heh).
I just use 1/4" clear surgical tubing and a jar. I can see the fluid color, which was pretty yellowed. I can also see if the fluid is ejecting by keeping a bubble in the surgical tubing as I bleed the brakes.

so far, so good. They firmed up quite a bit. Brake warning light in the dash won't shut off, though.

 

nope

a "weak" booster would result in a hard brake pedal.
To see what I mean, shut off your engine and then pump the brake pedal 5-6 times to deplete the vacuum. The brake pedal will get hard as a rock

 

I drove it, pulling a horse trailer, 900 miles. The trailer brakes helped greatly. After driving about 100 miles, which is the farthest I've ever driven in at one time, the brake pedal stopped returning all the way. This caused the brake lights to stay lit and the trailer brake to stay engaged. I had to lift the pedal with my foot every time I braked for the rest of the trip. After arriving at my destination and parking the truck for a week, the pedal returns to its proper position now. What the heck?

I tried the booster test, but can't say for sure it was hard as a rock. Could still be the booster causing the pedal to not return to its proper position?

 

If the booster was not returning you would have dragging brakes, not a soft pedal.