boogerschnot

So, I thought my master cylinder was bad.. Replaced it using the lifetime warranty through Oriley's. have pressure at the MC now but am trying to figure out what is going on with my differential pressure switch and my rear brakes getting no pressure.

The day I decided to change a rear cylinder, I had locked up the rear wheels in a panic stop and when I got home the brakes felt a little more funny than usual. I found some fluid on my right rear wheel and then a leaking cylinder. Replaced it and when I tried to bleed it I found that I was getting no pressure or very little fluid movement at the rear wheels. The fronts work great.

I am reading that some cars have a combination differential pressure switch/valve, and some may have a residual pressure valve for keeping pressure at the rear discs?

My diff pressure switch looks like nothing in the haynes manual, or any other write up's. Please look at the pics and tell me what I have going on. I would love for my rear brakes to work again. thank god Im not using it as a daily driver now days.



My little interpretation..

1slow67

Gonna guess its like an old proportioning valve or something.

guitarman376

Yea I bet that thing is an old PV or RPV. FYI when I did the cobra brakes on my car I did not install a RPV, although I still have one sitting in a box. No problems with it so far, sometimes the first brake pedal push of the day fills the drum lines/rear cylinders with fluid before making the car stop.

jlg2002

If you have a brake switch it shuttles to the low pressure side and shuts off flow in that direction. There is special tool that puts the valve in the center so it can be bled.

boogerschnot

Yea, ive read alot on the differential pressure switch and even found a picuture of where one guy sawed one in half. The shuttle didnt shot off flow in that case. I think i may have a blockage. Iill just have to get off my butt and chase it back from tge MC.

Al Newman

If you plug in the electrical contact on the distribution block, your "no brakes" light on the dash will not go out, I'll guess. The distribution block has a slide valve within that needs to be re-set. The other block in line to the rear brakes is a proportioning valve found on cars with front disk brakes and rear drums. If you get the slide valve re-set and still have no rear brakes, the proportioning valve is blocked. I would remove it and see if I could service it. Whilt I've rebuilt the distribution blocks, I've never jacked with the prop valve. The prop valve is the type found on 1967 Mustangs, usually on the rear axle, and was sold by Ford as a service replacement for all early Ford applications. Your distribution block appears to be 1968 or newer.
Best,
Al

chockostang

The distribution block is 68 69 Front Disc Rear Drum, But the Proportioning valve is the Ford service replacement type.

The replacement type is different in shape, size that the tube shaped original.

If no fluid is coming out of the OUT port of the Proportioning valve, there is a blockage somewhere.

Back track a joint at a time till you find flow.

If the Valve is plumbed as your drawing, it may not be right. See picture

Dan @ Chockostang