Brakes not working, need help

[Jay]

And that is about all I know about brakes.
So, i tried to bleed the rear brakes, but no fluid came out.
Fluid comes out of the front ones.

The truck will come to a stop by the brakes if it is slowly moving forward, but not backwards.

Pressure at the pedal is very very slight.

It appears to be a stock 67 system, all drums.

I took this to be a problem with the master cylinder or the booster, so I took them out to see if I could see anything. The pictures are attached.

What I am wondering is if anyone has an idea of what the problem is, and then hopefully a solution

[shrektruck]

You're scaring me. The master cylinder and vac booster both look pretty rough.
There's a lot to doing your brakes properly. If you remove the master cylinder you'll need to bleed the new one before you put it in and then bleed the entire system. Starting with the cylinder farthest from the master cyl. If you don't have patient help you'll need a one man brake bleeder.
While you're in there check all your wheel cylinders and lines real good. If the hoses look anything like the master cyl and booster you need new ones. Agood check of the system should tell you where the leaks are.
Don't forget to replace any worn hardware.
That's the basics but there's a lot more to look out for. If you have a digital camera take a pic before breaking down the wheels, everything must go back correctly to work right. free up the auto adjusters and put a little anti-sieze on the threads before reinstalling.
Man! I'm sure I'm missing something. Guys??? Brakes are the one thing you don't want to screw up.

[Jay]

Hmmm... never good when I scare people with my mechanic work, heh.

I was hoping I could just kindof fix them, is buying a new booster/cylinder the only fix? I attached a shot of the brake lines, let me know if theres any other pictures you would like to see.

[1968_ONEHUN]

Jay.First,did you detatch any of your brake lines at the master cyl ?It appears you did'nt by the photo.Is the rear resivoir empty in the master cyl ?If so,this is why no fluid came out,while you were bleeding.My suggestion would be to re-fill master cyl,if it is empty.Open your rear brake bleeder screw,pass. side,and pump up brakes till fluid does come out,checking master cyl resivoir regularly to see it does not empty of fluid while doing this.Once fluid comes out have someone close screw while bleeding,close pass side,bleed dr. side,and close..Jack up rear pull wheels/drums,and have a look at your rear wheel cyls for fresh fluid,front and back.If wheel cylinders are dry front and back,then the problem is between master cyl and before rear wheels.Probably master cyl.

[Jay]

The truck did sit for about a year and a half in a wet environment, an island actually. When I got it there was still fluid in the master cyl, and i topped it up to a quarter inch below the top. We tried to bleed the rear brakes, but no fluid came out after about 20-30 brake pumps.
Should I just keep trying until it does? I figured it meant that the problem was with the vac or the master cyl.

How would I check for leaking in the bore of the master cylinder? And how would I check for vaccuum in the booster?

Thanks for helping with this, I was at a complete loss this morning.

[sdranch71]

Check also that the bleeder screws will pass fluid. They have a very small orifice in them that will easily clog up from gunky fluid. Unscrew one bleeder screw at a time all the way out, and slowly pump the brake pedal to see if you get any fluid out directly from the wheel cylinder.

[flyboy2610]

http://www.classictruckshop.com/brake_rebuild.asp

[willowbilly3]

You will need to cough up maybe $300 for parts. On a truck this old that has been sitting, don't mess around trying to just get them working. Take your time, be patient, ask us a lot of questions and go through the brake system from one end to the other. New wheel cylinders, hoses and master cylinder. You might get by with your old shoes and hardware if they look real good but really it is best to just do it right and be done with it. Use Dot 5 silicon brake fluid as it won't take on water (hydoscopic?)
Another good idea for you would be to get on ebay and get a set of factory service manuals.

[Joe Kriston]

What is the proportioning valve? Is it that thing that's mounted to the chassis that the lines from the master cylinder are connected to?....My mechanic told me mine was probably bad,and that was why my break light stayed on...Where can I get a replacement?...It's a 1970 with power brakes....

[FORDification]

Don't confuse a drum brake system's distribution block with the disc brake's proportioning valve. The drum brake system doesn't require any front-to-back proportioning, but the differences in front discs and rear drums DO require a proportioning valve:



If your brake warning light on the lower left of the dash is staying on, it probably means the switch in the block simply needs to be recentered, or reset.

[Joe Kriston]

Keith,

Hold on a sec...let me double check...

All right,I got the one on the left....Isn't there something in the distribution block that goes bad ?....Are you saying there's no kind of valve in there?

[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!