Hey team,

I have an 1984 F-250 with the 6.9L Diesel. I bought it a few weeks ago and noticed the rear brake line was broken off and the brake light was on in the dash. I disconnected the proportioning valve and it turned the light off. I disconnected the rear brake line from the valve and blew air down it to see if was full of gunk and surprisingly, barely anything came out but air (i.e.no fluid). I have the line completely disconnected from the valve and I still don't have any fluid coming out and the pedal is still firm. What is my problem? Why don't I have fluid coming out? The line running from my new (full) master cylinder to the valve has fluid and it is clean/open. Is my valve junk?

Thanks for any help.

 

I took one of those things apart once, it was a valve from my 1981 F350 4x4 gasser. Might be the same thing you have (but not that an F150 will have).

I have it in a plastic bag in the garage, I'll hafta look at it to make sure but I honestly doubt right now that valve is your problem; IIRC I don't think it even COULD be the problem.

I'll see if I can take pictures of mine and post 'em later................

 

This might take me a while, so you should check to see if your master cylinder is in fact pushing out fluid to the rear brakes.......

 

I bought a brand new rebuild master cylinder and installed about a week ago. The front brakes work fine. I'll take the rear line off at the valve and see if I have any fluid movement. Then I will know for certain if I have movement in, and none coming out...there is something bajankity with the valve.

 

I have had a break through....I had the line disconnected from the master cylinder to the valve and everything was working great to that point. I still had the rear line removed (heading to rear of truck) and decided to really push on the brake pedal to see if I could get anything. Well, I pushed pretty hard and BOOM the pedal dropped to the floor and I heard a clunk. It appears as though the rod inside the valve pushed completely out and was full of nastiness (i.e. dirt). I cleaned it up and evacuated the master cylinder. It's too dark here to do anything with it tonight but I will remove it completely tomorrow and clean it up and see if I can get it to work again. The bright side is that my brake light is finally off

 

Cool, thanks for the update!

So, I looked at mine in the garage, I have to say I have no idea how they build these things...

Mine looks to be just a brass block with some holes bored in it; I seem to recall being able to see light through the holes but must have been mistaken, I couldn't replicate it.

The factory shop manual shows two cross-sectional diagrams of different valves, yours I think is different than my F350's.

In any case, given what you've found with yours, I would thoroughly flush that thing! Probably even take it apart to do it (but be VERY careful, new ones are a few hundred bucks).

 

New development and PROBLEM...I put the rod back in the proportioning valve which was pretty tight fit and needed to smack it in. Once in, it seemed like it was tight and ready to go. I reinstalled and bled the brakes starting with right rear, left rear, right front, and left front. I noticed I had brake fluid coming frmo the valve area and inspected. I have brake fluid coming OUT OF THE ELECTRICAL CONNECTION (i.e. warning switch). Grr! What does this mean? Are the o-rings bad? Do I need to take apart again? Do I need a new warning switch?

 

I would go to the junkyard and get a valve, or just take it out of the system.

It serves as a junction block for the lines to split off, and it also delays the rear brakes some so they won't lock up in a panic stop. In other words it "proportions" the pressure front to rear.

That all being said, you can have good brakes if you want to delete it. It will be reverting it back to 60's and earlier era brakes that didn't have a valve. There are many very late 80's/early 90's pickups running with straight brake lines(including my 89), because Ford came out with a "better idea" and installed a rear anti-lock system(they didn't have a proportioning valve like yours) Like your system, it works well when it was new, but now it's old, it's very expensive and hard to find parts for, so you do what you have to, to get a truck you can use.

 

Look back at Chris's first picture. There is a small pin sticking out of the rubber.Figure # 4 calls it a bleeder rod. Grab this with a pair of vice grips, and pull towards the front of the truck, while someone steps on the brakes.This centers the valve. The leak will have to be fixed. As far as I know, there are no new, or rebuilt valves available. Nor a kit to repair them. Junk yard is your best bet

 

The differential valve (shuttle) is meant to move over and block flow in the case of a total rear brake failure.
It also sets the light.

With the 350 style the rod goes in to reset and purge the system.
With the 150 style you have to pull out on the rod with a pair of pliers.

But I certainly don't know everything about them.

 

Hey, Charlie & Jim,

On my 350 valve in the picture, is there also a rod/valve/device that's supposed to slide back & forth?

I removed both end pieces and tapped lightly on the stuff in the center but it didn't give any indication at all that it was gonna move.

That 350 diagram that Ford provides is confusing as all get-out to me with all those diagonal lines.

Should I beat on it? I got this valve from a JY mostly to take apart & learn from, never really intended to use it but would rather not destroy it if I can avoid it.

(BTW I seem to remember looking 'em up before, I think maybe LMC had 'em but they were close to $300.)

Here's the valve with the end pieces removed; the last one is where the switch goes:
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Chris,
You can see the shuttle = "differential valve"in this section drawing... and the step in the bore at the "Front" side.

Now that you have unscrewed the hexagonal part and the spring loaded switch it should come out the rear brake pipe outlet end, to the right of this drawing.

 

My main question now is...should fluid be coming through the switch? Is the area where the switch is located under pressure. I ask this simply because the switch is 100% plastic and 27 years old. I did an air test and found it is a solid seal while the pin is completely relaxed. If I break the seal at all (i.e. valve being out of alignment) I notice air coming out.

Looking forward, my plan is to recenter the differential valve and install. If after bleeding, the switch is still leaking I will remove the switch and file down the pin. If that still doesn't work, I will cap off the switch hole with a bolt. If it all goes to hell in a hand basket, I will find a replacement at a junk yard or do my best to bypass the valve completely. Do they make two into one blocks for brake lines?

 

There should be O-rings on either side of the shuttle to seal the switch from brake fluid. (at least it seems so from the drawing)
You can find solid brass "Tee's" to split the front line.
But I do not know what the thread sizes are from the drawing.
Be SURE to get a T with the proper seats for the reverse flare on the ends of the brake lines.

 

Yup, you're right, thanks!

I have historically broken things my entire life by applying too much pressure, am trying to get away from that.

Do you know if the O-rings are a standard fare that can be gotten at a hardware store? Or are they a special rubber that resists brake fluid or sumthin'?
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