My 1975 f150 has pooey brakes...

My 1975 f150 has pooey brakes....they feel soft and feel like most of the braking is being done by the backs (back brakes lock easy, front doesnt dip when u brake hard)

Everything except the proportioning valve and the front calipers has been replaced, is it safe for me to assume its the valve?


Also questions that dont deserve their own thread thread.

Have all the steel hard lines been replaced?

Only rubber, no leaks in the steel lines and they were flushed out. I get pressure front and back.

I'm dealing with the same problem with my '86 F250. Feels like I have no power brakes, its all mechanical and I have to step on them to stop at all. But some times the pedal goes to the floor, other times it's as stiff and hard as can be.

Mine may be vacuum related cause diesel tho. who knows

>front calipers
Does that old thing actually have disc brakes?

Yes. Most 70s autos do.

The lighter weight trucks could be optioned with all drum though.

How old is the Master cylinder? Is it a single or dual master cylinder? I would suspect that before a proportioning valve.

Its new and i replaced the old _also new one under this suspicion)

Its dual chamber

Could be booster. Pull hose and see if its wet with brake fluid, unless its hydro. The, i dont know. Also sounds like a bad master.

If you have access to a power bleeder I would use that to make absolutely sure all the air is out of the MC.

Have you checked to see if the calipers are moving freely? Pistons and slide pins?

Have you bled out the fluid and renewed it?

Its been bled but not flushed. One caliper seemed like it might be sticky but other is fine..

Dont got, i bench bled it though.

Is it pulling to the side under harsh braking on the side with the suspect caliper?

Probably worth pipping it off and freeing up the slide pins and repacking them with high temp grease, do it on both, you'll probably find the pins are pitted and corroded.

Change the fluid and free that suspect caliper, clean the pad wells on the caliper carrier too and copper grease the contact areas of the pads.

You said you replaced parts, are they all correct and matched up? Make sure your master is the right size for your calipers

No, it actually isnt. If you'll read my original post it describes the way they act.

Are there any good comprehensive books on learning how auto engines work or how to diagnose and repair them?

Would buying said books along with a

Yes, they are correct.

If you have the money....a chiltons manual and a old car works fine.

Also these calipers don't have slide pins. Its a one piece caliper.

maybe ur fuckin cars broken bud

yes and another thousand for a comprehensive set of amateur tools

The internal rod on the proportioning valve may have moved or be stuck. Their should be a small to push a little to reset its position. or it might be jammed with shit and stuck.

Maybe i just told you to read my previous post for symptoms instead of making needless wasteful ones like these "bud"

...

Are your drums adjusted? No trapped air in lines?

Thank you, I will check that.

Yes, and as far as i can tell also yes.

Could be collapsed front hoses not letting enough fluid flow. It's rare, but I've seen it. Unless they're relatively new?

They are brand new.


Also to everyone else i tried pulling the pin to rest the valve and it appears seized so i guess i have my answer.