I just got done plumbing and installing my rear disc brakes for my 79 f250. Has dual pistons fronts Dana 60 and rear singles for a squarebody on another Dana 60. No fluid to the rears. Will not get past the proportioning valve. Took it apart and cleaned it it saw smudged up. What is the best procedure for bleeding brakes with this kind of issue. What do I do to keepp the piston from blocking the rear brakes off. This occurred when the rear drums failed a few years ago and has been parked up until just recently. Which way does the proportioning valve bleeder need to go as well? Has fluid at the valve but won't flow to the rears.

 

I'll start by saying that I have no direct experience with F-Series versions of this. Hopefully basics are transferable.
Looking in the workshop manual I show a differential valve incorporating a brake pressure warning switch.
Typically a lack of hydraulic pressure on one side of the valve means that the hydraulic pressure from the other side pushes a free floating piston across restricting or blocking the unpressurised hydraulic line.
Some of these valves incorporate return springs to re-centre the valve when no hydraulic pressure remains but typically you have to re-centre them manually. Normally this means unscrewing some form of blanking plug at one end. typically the brake warning light switch is removed and left removed during the bleeding process.
Once the valve is re-centred the system is bled using only partial (typically 50%) brake pedal travel only.

Reading the workshop manual I've found a combined 'pressure differential and proportioning valve' which incorporates a bleeder valve which must be held open with a 'metering valve bleeder special tool' (J-22742) which looks like it can be replaced with a screwdriver and a pair of vice grips.

The valve:
http://cimg8.ibsrv.net/gimg/www.ford...8362f70318.gif

The tool:
http://www.fordification.com/forum/v...ic.php?t=45503

 

From the Haynes manual:

"Vehicles with a GVW under 6800 pounds must have the rod pulled out. Vehicles with a GVW over 6800 pounds need the rod pushed in.

 

*deep in thought now...

If you have just fitted disc brakes to the rear and the proportioning valve is fitted to vehicles with rear Drum brakes, is there any reason to still have a proportioning valve in the system?

 

I would think there is. The valve is set (if I remember right) to put more pressure to the front than rear for F series.


There is a pin that does need to be held out on the Original F series valve (under 6800 GVWR). Also did you start bleeding it at the rearmost caliper?
I had the same issue and I wound up replacing the proportioning valve (I had drum brake rears though). However beware that ford doesn't make a new valve. Or rebuild kits. Ones for the 80's trucks work though. You just need to change the brake sensor wiring. (combine 2 wires into 1).


Mack.

 

"The proportioning valve DOES NOT act like a valve to shut off fluid flow. The valve serves a couple of functions. It acts as a proportioning valve to regulate pressure front and rear to keep the rear brakes from locking up because drum brakes require less pressure to operate than disc brakes.

The second function is to signal brake failure. The way it does this is there is a small spool valve that is between the front and rear brake circuits. This valve is a small shaft that has a groove in the middle, the switch that controls the brake failure light has a pin that sits in this groove. When the valve is centered and there is equal pressure on both sides, the switch's pin is extended and the switch is "off".

If there is a failure in either the front or rear brakes, when you hit the brakes, the high pressure from the side that is still functioning will push the valve towards the low pressure side. This pushes the groove away from the shaft effectively pushing the pin in and turning the switch "on".

This function is there strictly to turn the warning light on or off, nothing more.
If a dual master cylinder is used, the front and rear brake systems are effectively isolated from each other and a failure in one system will not affect the other system.

The drum/drum isn't actually a "proportioning" valve but rather just a pressure differential sensor. It does use the same style valve to trigger the system failure warning light though."

Sounds like you got the floating pin stuck on the rear side of the pro valve. I am trying to remember what other FTE members did when they did a rear disk swap and had similar issues. Have you used the advanced search?

Here you go, a couple of these look like the answer might be in there. https://www.ford-trucks.com/forums/s...rchid=26075953

 

I had this problem, and I fixed it by replacing the stock valve with an adjustable one from Wilwood.

 

Me too. But I went with another name brand.