Hey guys, I have a 78 f250 custom with a 351m. I recently fully replaced all the brake components (everything) minus the proportioning valve. Not sure if it matters, but I have speed bleeders on the back and normal ones up front since no one in town stocks the size for my fronts. Yesterday I finished hooking up all the new stainless lines. I began bleeding, getting lots of air out and tightening any connections that appeared to have slight leaks or pooling of fluid. I am now 100% sure that nothing is leaking and all connections are tight. Here's the problem, my pedal is still soft and going to the floor. I went through all the lines again, bleeding and checking leaks. No leaks, but still a good amount of air. Pedal is still soft and still goes to the floor. Third time around, bleed and check leaks. NO air and No leaks. Why is this pedal still soft and going to the floor? I did bench bleed the new master cylinder (ran lines back into itself and pumped until no more air bubbles came up from the reservoir). At this point, I was going to bleed again, just to make sure but after that I am lost. Any suggestions? I did hear about some pin that needs to be reset on the proportioning valve? I'm not the most mechanically inclined, but can definitely figure **** out so I am pretty bummed at this point that I can't finish the job. I want to drive the truck again!

 

Crew cut, This may sound weird but have you watched the flex hoses while someone presses the brake pedal? I have seen defective brake hoses. Kenny Nunez

 

I have watched them, but not real close looking for anything in particular other than leaks. What defect should I watch for?

 

You are correct; the front pin must be pulled out while you bleed the fronts. I doubt that's the cause of the problem, but you should go ahead and rebleed the fronts properly just to take that out of the equation.

When you bench bleed the master cylinder, how far were you able to push the cylinder into the bore when you were done bleeding? Once it's done properly, it should be so tight that you should not be able to push it in more than 1/8 of an inch.

 

I guess I worded that wrong, I did the master cylinder bleeding on the truck because I bought it already connected to the booster. I just put it all on the truck as one and did it with the pedal. Could this be the reason? I know it's not the ideal way, but I didn't think it would turn out this bad.
Also, the little ratcheting adjustments on the rear drums, are they the actual adjustment of the rear brakes or JUST the park brake?

 

I read through some other threads about the valve. I believe my pin is stuck out. Its about .25-.5 inches pushed out. I cannot move the pin even with vise grips. Also, when I turn the key to the on position my brake light does not turn on but my seatbelt light does. When I turn the key further and start the truck, my brake light then flickers once

 

So I tried the proportioning valve and rebled everything. Nothing. Any advice?

 

It's not gonna bled on the truck. To get the air out of the master they need to be bench bled. The plunger isn't bottomed out while on the truck and can only be done right to get all the air out on a bench.

Also if the proportioning valve pin doesn't move then you need to replace or rebuild it; as far as I know.... Ford wants that pin pulled out when bleeding for a reason. When working correctly the proportioning valve also is a warning system for brake failure; which is a good thing.

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Crew cut, It is possible that there may still be air in the master cylinder, on the brake hoses, just watch them when the brakes are on, if they are defective you will see them "balloon" under pressure. The self adjusters on the rear wheels must be adjusted manually when new shoes are installed. With a brake adjusting tool inside the slot push down to rotate the adjuster star wheel repeatedly until the wheel is almost locked, then go the other way until the wheel is free. It will take more effort to rotate the star wheel the other way because spring on the self adjuster . The self adjuster maintains .010 clearance if everything is working right.

 

I just did a '78 F250. I bench bled with little jumper hoses going back into the master while it was mounted on the truck. I didn't know the trick of pulling the pin on the prop valve. It probably took me 4 quarts of fluid to get all the air out. I did it the hard way but it did work.

Suggest you bench bleed the master again. Make up little jumper hoses to feed fluid back in to the master. Then re-bleed the whole system. if the prop valve is suspect, get a new one. I believe Inline tube carries them if you can't it find locally.

 

This absolutely could be, and probably IS the reason. Bench bleeding is called "bench" bleeding for a reason. It has to be done in a vice. You cannot bench bleed it in the truck because it won't be level, and the pedal won't give the full stroke.

Take it apart and do it the right way; you're stuck until you redo that step correctly.

 

I installed discs on the front of my f100... Been having issues with the brakes either remaining slightly engaged or the pedal completely dropping where I have to pump once or twice to get pressure back. I am thinking my issue involves the plunger being to far out and some more air perhaps although its got to be minimal. The moral of the story is next time I change as little as possible and get it working right before moving on; should make trouble shooting a little easier by narrowing down the possibilities.

 

Before bleeding brakes:
Always start with adjusting the rear brakes as per Ford procedure (all the way tight then back off till you can turn tire).
The reason is even if you get all the air out of the system you will still have a low and soft pedal unless the rears are adjusted correctly.