Brakes not working, need help

[FORDification]

Well, I suppose you could call it a valve, but I think it's more of an electrical switch. When you loose pressure in either the front or the rear, the switch gets off-center, turning on the dash light to alert you to problems. You simply have to re-center the switch by bleeding the brakes. Crack either the front or rear brake line while a helper pushes on the brakes very slowly until the light goes out. It'll probably take a time or two to get it just right. It's really kind of a PIA to get centered...more annoying than difficult.

I have a scanned article around here somewhere on the proper procedure for getting that centered. I'll try to dig that up and post it for you.

[Joe Kriston]

I just thought about what I just asked,and I guess that would fall under the category of a stupid question...The fact that it is not a proportioning valve would indicate that there is no valve in the distribution block...So I don't have to worry that I have front brakes only,...or rear brakes only...That light should only be one when there is a problem with the brake fluid system,no?

[Joe Kriston]

Thanks,Keith...We posted at the same time...My mechanic told me that the Ford book he had said that those blocks were not serviceable.....and he could not find a replacement anywhere....He may have been talking about centering that thing like you were talking about...But he said that was the reason my light stayed on,and that he wasn't sure exactly what,but that my brake system wasn't operating at it's maximum...

[FORDification]

Well, I guess the factory DOES call it a valve, and after seeing the schematic in the manual, I'd have to concur. However, I don't think the valve is bad, I just think it needs to be recentered.

Here's what the piece looks like:



and here's what the manual says as an example of how the valve works:

Should a failure of the rear brake system occur, hydraulic fluid pressure in the rear brake system would drop. During brake pedal operation, the fluid pressure buildup of the front brake system would force the differential valve toward the low pressure area (secondary system outlet port). Movement of the differential valve forces the switchy plunger upward over the taper shoulder to close the switch electrical contacts and lights the warning lamp, signaling a brake system failure.

...and here's how it describes the proper procedure for centering the valve:

Turn the ignition switch to the ACC or ON position. Loosen the pressure differential valve inlet tube nut of the unfailed system, or teh side opposite the system that was bled last. Operate the brake pedal carefully and gradually until the pressure differential valve is returned to a centralized position and the brake warning light goes out. Tighten the tube nut.

Hope this helps....good luck!

[Joe Kriston]

Thanks,Keith...I'll show that to my buddy...It's a little too technical for me...The only thing I'd know to do is to tell a few jokes and try and cheer it up because the schematic says the warning light plunger is 'depressed' : ...

[Jay]

Hey, I'm finally back with some updates.

I replaced the booster, this helped with the pedal being very sticky. Now it moves up and down when you press it, and springs back. Good stuff.

Trouble is, it doesn't do much more than that. I was able to bleed each brake, that went just fine. However, I've lost about 10oz of brake fluid out of the smaller compartement of the master cyl, and I have no idea where it's going.

Also, if i take off the master cyl, and reattach it, brake pedal feels normal. If you press hard, or repeatedly pump it, there is a jolting and loud thunk. After this, the pedal becomes really loose, but will still put brake fluid out of a bleeder.

My idea is that the fluid is leaking out of a wheel cyl, and when enough is lost you don't have enough pressure in the system to do any good.

What do you think?

[FORDification]

If it's leaking somewhere, you'll know it....go around to each corner of the truck and see if there are any puddles of brake fluid running down the back to the tire..

I don't know...sounds like maybe the jolt or thud you report might be either a sticking wheel cylinder or a problem with the linkage. Kinda hard to tell any more from what you're describing. Where does it sound like the noise is coming from?

[Jay]

I would say it feels like the master cyl, but i am not sure. That general direction though. Think it's worth replacing? It functions fine as far as i can tell, squirted liquid when i took it off and tested it. And yes, i did bleed it before putting it back in. Could be broken though?

And I really can't find where all that brake fluid is going!

I have poured in a whole lot, hoping it would show up, but no such luck. Traced all the lines, checked all the tires, looked in a general area under the truck, no signs.

[Jay]

I checked the front two brake assemblies yesterday, and they seemed to be in working order. The wheel cyl pushed when the brake was pushed down. It did not move the rear caliper very much at all though, I think once the front one encountered some pressure it would expand the rear one ok. The springs also brought things back into position just fine. Things were a little dusty, but the rust buildup was not intense.

Oh, also the brakes were only moving once the pedal reached the very last inch of it's travel, after about 10 inches of movement.

I thought I would check out the rear assemblies today, I've heard it is more complicated though, so we'll see how it goes.

[Jay]

uh... huh.... they uhm... seem to be working?

I did not really change that much though. Took both front wheels off, undid and reattached the master cyl. Then the pedal felt different, so i tried it out.
They brought the truck to a stop, but i was able to overpower them with the horsepower from the engine.
The travel of the pedal was very light for the first 3 inches or so, and then it seems to hit a very solid resistance.

Is this normal? Should I let the person I sell it to know that they might die?

it is a 67 with 4 drums and vac assist.

[jor]

Jay,
Did you ever do the suggested diagnostics on your rear brakes? i.e. test to be certain your hydraulic system is actually pushing fluid into those rear brake cylinders. I'm starting to think Willow's suggestion is the one you need to employ - replace it all for $300-$400. Good luck.
jor

[Jay]

The truck went to a mechanic for their review, and they thought an entire brake job was necessary, i can't really afford that though. There is a guy with a 1970 f250 that would sell me the brake system (missing only the master cyl) for $75, he said the brakes always seemed fine to him when he drove it, and that the front was power disc.

p.s. i've been gone a long while, because I thought I had sold the truck. The guy ended up declining because it lost oil and had some other problems. My opinion is it's 40 years old... heh

[Jay]

haha watts, you hit that one dead on. I keep doing these things and thinking hey, i might as well keep it now that...

I think I am just going to let it go though. Hopefully I can find someone that will take proper care of a great old truck. And thanks everyone, i had a great time here. Expect me to drop by in the future.