I need some Ideas. I am refurbishing a 77 that had set for 4-5 years. I had to replace the front calipers because they were sticking badly. I pressure bled the fronts thru the master cylinder. On a test drive the brakes seemed to work fine. The rear brakes worked, but I decided to bleed the rear system since I figured the brake fluid was a mess. I used a suction bleeder untill I was getting clear fluid.
Everything seemed normal untill I checked the brakes. Then I found I was geting no brake action on either rear wheel at all.
I Then tried to pressure bleed thru the master cylinder but never got much fluid to flow. So I tried some one way "auto bleeder valves" and got good fluid flow. Still no rear brakes.
I had my kid help me bleed again the old fashioned way. Good fluid flow and no air bubbles. In total I have run two large bottles of dot 3 thru the system! but still no rear brakes. I pulled the right rear drum off and watched while the brakes were applied. Zero movment of the slave cylinder.
I can't figure out what would keep the slave cylinders from actuating since I know I get fluid flow all the way back to the the bleeder screws. Is there something in the system that could be porting all the pressure to the front?
I did nothing with the proportioning valve as my old repair manual said nothing about it and I did not realize it needed that pin pulled. plus I thought that was just to let fluid go to the front calipers.. And I have bled brakes on other vehicles without messing with the pin.
Any help apreciated.

 

I know you are supposed to pull that pin on the proportioning valve when you bleed the brakes, so I think you should try that to see if it helps.

 

That depends on the GVWR Cujo.

In P-47's case you are correct though and it is only for the front's.






The Ford braking system works this way.

The Rears come on first then the main braking is taken over by the front's.

I suspect your BPPV as well.

After these trucks sit for a time...they can develop problems from moisture which can destroy a BPPV .

 

Mil1ion,

Do you have the pictures for f250/f350 over 6800 lbs gvw?

 

Photos of what specifically ?

 

I don't know if this would help, but Mine stuck one time and I didn't have any front brakes. Man when you don't have any front brakes "You Don't Have any Brakes."
I had my wife stomp on the brakes while I pounded on the darn prop valve. It worked the darn thing is fine now. That was about 15 years ago and it hasn't failed again.

 

The proportioning valve, the last picture you posted says its for up to 6800 lb gvw.

 

So do you have an F350 then ?

You didn't say what you had..just that it is a 77.

 

I appreciate all the help. The truck is an F-150 4whl Drive. I do have it working now. I finaly decided to pull a slave cylinder and look. It was so gunked up and rusty I don't know how it worked even when I first drove the truck before changing the calipers. The other side was just as bad. My guess is that the slave cylinders sort of worked for a while until debris piled up and blocked them and/or they stuck on a rusty patch. I replaced them, and re- bled them and I now have brakes.
I was having a hard time believing in the coincidence of both sides failing at the same time. In hindsight when I realise that since the truck had been sitting for five years, it isn't really a coincidence..
I now have a firm pedal allthough if I hold the brake hard for awhile it slowly fades down to the floor. Anyone know if this is likely just a little air in the system or is it likely that the the master cylinder also has problems? or...?

 

Master cylinder.

Find a new one made with a stainless steel sleeve not cast metal.

Slave cylinder ?

I think you mean wheel cylinder.







I have do the brakes on both of my trucks.

Good thing I have collected new parts over the years just for this occasion

 

Maybe I'm dating myself with my terminology, but the wheel cylinders ARE slave cylinders. So I guess either term is acurate. Wheel cylinder would be a little more specific, since you might also have a clutch slave cylinder (although not in this truck). Anyway thanks again for all the suggestions everybody.