Over the past 2 days I have been trying to isolate my brake problem and reached out on some help on the form. Got many responses to this problem. It was the combined answers that lead me closer to this problem.
After searching for past posts on Proportional Valve & Differential Valve I also found many people searching for answers to the same type part with varied problems. I could not find any information to help me. MikeoOoOoO was the most informative about this issue.

I am a simple person and no expert by any means. In fact I know almost nothng about trucks and engines, I'm a carpenter by trade. So I often ask myself why I bought this 77 F100 to restore however I am finding it fun and the people on this site are very helpful.

So in the future others my find this information I am posting what I have found about this issue so far.

As MikeoOoOoO said the proportional valve is used to mediate the flow of brake fluid to the rear and front brakes. If one fails the vealve has a piston in it that automaticly moves to the low pressure side closing it off to not have a total brake failure. Meaning if you were driving down a road and something clipped you rear brakes (or front) the valve would quickly close the line to the rear so the front still maintain pressure. If you clip both front and back at the same time you need to thrust your feet through the floor board and Flintstone stop the truck.

Now these valves were used on many vehicles during the time so this applies to all vehicles with this type valve.

My cousin (past mechanic and very good too) sent me a scan of a old book he had that explained the valve issues and some bleeding tips. Unfortunatly I am unable to turn the page so you have to read with your head sideways but I am finding out this is typically the way mechanics work all the time in very stranger positions than sitting at a PC, usually with dirt and grease falling in my eyes too.

So in laymen terms I will try to explain what I have learned so far. Keep in mind this is manual brakes. I have no idea about power brakes. I hope this can help others as I have found no real good past posts that helped me.

The valve is referred by many as two things. Some call it a proportional Valve and others a Differential valve. The wire at the top is not the rear brake lights as some have suggested. This is the warning light in case the rear or fron fail or loose pressure the valve (piston within the valve) moves to the low pressure side closing it off. In the middle of the piston there is a grove that the switch (where the wire connects) gets activated if the piston moves either way (rear close off or front close off). This button will activate the brake light on the dash.

I have read this button can often fail or get stuck even if the brakes are working fine. In my problem I have fluid at the front but not the rear. So apparently my piston is closed at the rear (see the book scan below). They suggest how to get the piston to move back to the center position. This is where the button should release and shut the brake light off. If not the button is stuck. Just remove the button switch and try to un-stick it. If that does not work get another. It screws in and out with a wrench at the top of the valve.

If you have flow on the front or rear but not the other, like me. The valve is stuck closing one side off. The book information explains how to get it back to center.

I hope this helps people because a new valve is $250 bucks if you can even find one.

Keep in mind as you open the bleeder valve at each wheel the prop. valve or diff. valve will act as if there is a low pressure problem and move to close it off. It's like a seesaw so those who have pressure on all 4 wheels and the dash light is still on, get a new switch. those who think you valves is bad (like a lot of the posts I read) it might not be. Look to see if the piston in the valve is to one side or the other closing off front or rear brakes line fluid.
Now I suppose the piston could be stuck as well. I was told you could take them apart and look to see if it is frozen or working properly. I will find out tomorrow as I venture under the greasy truck to fix my problem.

Again, please do not tear me apart in my dissection on this issue. I am not a mechanic. I was just trying to help others avoid searching for the information I have listed above that took me days to find out. And a lot of frustration. I will post my findings tomorrow after I figure this out some more.

Addition: A member "77&79F250" below made a good point and I wanted to ammend the original post to include his comments. (or you could just scroll down). It is important to check that you have flow from the master Cylinder to the valve first before you determin the outflow was caused by the piston in the valve closing off the front or rear. Both lines too, front and rear lines.

Everyone was a lot of help too. If anyone has any more information on this subject I would greatly appreciate the input. I was just trying to lay it out in laymen terms.

My valve: (Ain't it pretty?)


My cousins book reference to the valve:

 

An excellent write up and a nice job filtering through all the responses on that other thread. Kudos to you.

Carpenter? Nah, A craftsman!!

 

Nice job explaining things in simple terms, I like simple terms. Thanks again for taking the time to make this informative write up. BTW have you got your pro valve issue fixed yet.

 

Thanks HIO Silver! I really value the form and only hope I leave it a better place when I contribute what I can. You are helpful as well and I appreciate all the people here who help me.

Really, it's difficult when you have a problem and your sitting at the keyboard waiting for someone to reply with greasy hands waiting on an answer. I only hope this will help someone else. It took me a dag gone hour just trying to write that post and upload the photos. Then word was inputting smilies into the post not allowing me to post it saying there was to many images. What I night mare.

I really do value the great group of Ford Enthusiasts so to me it was worth while writing because the help I recieve is free so I figured I would leave what I can behind. I'm still going to need a lot more help with the truck. I just got it a few weeks ago and I want to fully restore it. I will have a lot of questions.

Thanks again friend,

Bill

 

No, I am going to try to impliment the centering of the piston tomorrow. I can only hope the light goes out so I don't have to put a new switch ($33) But I am optimistic the valve is good and is not bad as most seem to think when they have Prop valve problems. I can only imagine how many people trow away this valve thinking it's broken. The valve is over $250 and most don't have it anymore.

Remember when the piston is center the light should go off however during bleeding you could cause the piston to move to the other side (the side your bleeding/ front or rear) closing it off again.

I'm sure there is a way to beed the lines without this happening however I can not find any information about this yet. All I can try to do is the combat the seesaw issue of it moving right to left.

Wish me luck. I may just take it off clean it up and take it apart to look at it. However I am going to try to bleed them out and get the piston center first. If that works I'll just clean it where it is.

The reason I can to this conclusion is I started at the rear wheel (because I had no fluid at either rear). taking each brake line off to see it it was clogged. They were all clear. Then when I removed the rear line at the valve there still was no fluid so I though the valve was bad. Now i find out the valve is suppose to close when the line has no pressure. Then my cousin sent me the mechanic book pages and it all made sense. He also said these valves although old usually do not brake much.

Like I said, I wonder how many people just throw it in the trash thinking it's bad. Hopefully this will help others. I will post my findings tomorrow but I'm hopefull it's going to work. Now that I understand the workings of the valve.

 

Did you ck the fluid at the master cylinder (front reserve for rear brakes) it is getting from it to the pro valve?

Might have an issue in the master cylinder if no fluid is making it down to it. A bench bleed of the MS might be in order.

 

Yes, the first thing was the Master Cyliner. I just replaced it. Got it primed up with a bench bleed and there is fuild in the rear chamber and flowing into the prop valve. The problem is no flow out of the prop valve.. Hence the explanation above.

I suppose that is a good diagnosis before tearing everything apart. I assume everyone does exactly what you say before going further. I am assuming most people would do this first. I started at the rear taking every line off checking for a clog. Then reached the valve to find out there was no flow there. Then I though about just what you asked and removed the in flow line to the valve comming from the master to make sure it was flowing in.

Good idea to mention that because I hope most people would do all that diagnosis prior to assuming it's the valve or the piston shutting of the rear or front lines.

Yes, good flow out of the master. My engin capartment has evidence of that as the plastic caps that came with the Master Cyliner blew out after the bench prime because I was stupid enough to push the brake pedal before I hooked up the second line. I was having a tooltime moment. Like I said, I'm no mechanic and my mistakes remind me how dumb I am each time I put my head under that hood. So dumb that I was removing the 4 bolts behind the Master Cyliner and there are only 2 that hold it in place. Thank God I did not remove the others (just loosened them) because I think they hold the steering wheel or somthing eles inside the truck. LOL, My luck it would have been the dash board............

 

I just read the thread and didn't see where you mentioned that fact, just trying to help. No offense meant, sound like going into the pro valve to recenter the valve/rod is in order.

 

No offense taken. Hope you did not take my reply as upset. I'm glad you mentioned it. I could have been as stupid to miss somthing like that. For some dumb reason when I reached the valve I instictivly thought of that however disconnected the line at the Master cyliner first to see if there was flow. Then my mind told me to check the other end at the valve to see if the line was clogged.

I suppose even the valve could be clogged as another compounding problem so I'm not even sure the valve will recenter if there is built up juck in there. I'm learning.....

I'll fill everybody in tomorrow what I find. I think it could be usefull for many in the future. I could be completly wrong but this valve looks very primitive and simple. However what I am trying to find out is how to avoid the valve closing while bleeding that the book mentions could happen while bleeding the line. Teater Totter kind of thing. Makes no sense.

If the valve is designed to close off the low pressure side (failure side) how the hell could you bleed brakes without it moving all the time. It seems as if there is a piece of the pie missing here and I am determined to find it out and tell everyone when I do.

There has to be someone who know alot more that just stupid old me. I can only hope someone weighs in here soon.

Thanks for the tip though. I was thinking I should have mentioned it in the original post. Brakes are simple however complex in the diagnosis as one problem can cause another. Crazy.........

 

No harm, no foul, I have heard on here you should pull out the little pin/button on the end or hold it out with a slip over washer thing during the bleeding process?

I have never done it myself and have had no problems bleeding brakes, that might be the solution to your teedertodder issue during bleeding?

Always start at the wheel cylinder farthest from the MS back R/back L ect... let us know how it all turns out.

 

Yes I heard the same thing from someone else. I bet you there is a tool that the mechanics in the day used to hold the piston stable for the bleed proccess.

I think the niple that sticks out on the one end my connect or be the piston the rides left and right. So holding it before you start (assuming it's center) would seem like the way it was done.

I will know better tomorrow because I am going to take it out. I bought some clear hoses from Lowes to connect to the bleeders to controll the bleed from shooting all over everything. I will have to empty the Master though. Is there an easy way to hold the fluid in the master with the lines disconnected other than those stupid plastic caps?

 

Stupid plastic caps and thread tape, also when you bleed the brakes put one end of a tub on the bleed valve (after you put on the wrench) and the other in a jar 1/2 full of clean brake fluid, prevents pulling air back in during the process.

As far a the button goes like I said I have never pulled it out to bleed mine.

 

Good tip. I'll do that. What about the fluid. I'm bound to loose a lot doing all this. Can it be reused (put back in the M/C) or should I just use new?

FYI: yes I think most will bleed without the problem I was discussing however, I think if pushed to hard (the brake pedal) it could shift to closed. I think most people more familiar with brakes (like you) don't overbleed or pound the brake like us amitures. LOL

 

My first brake bleed I shot brake fluid up all over the hood,lol.

PB blaster all 4 bleed ports so not to brake/strip.

Old fluid out always new clean back in, I bleed till new fluid is coming out the bleed ports.

3 person job, one to take take off/put on MS cover between pedal pumps, and keep MS topped off. One a little smarter to push pedal when told and tell you what happening to the pedal during bleeding.

And you under truck so you bleed ports do not get broke/stripped.

#1 fill ms, ms cap on, you wrench on port, #2 push easy, steady pressure, you open port till fluid starts filling jar/ #2 tells you what pedal is doing. When it hits bottom you shut close port, #2 off pedal. #1 top off MS , and here we go again.

You where eye protection aka sun glasses/shop goggles, brake fluid that's rusty is NO fun in you eyes.

Front MS reservoir for rear and big rear for front??

 

[quote=77&79F250;9284977]My first brake bleed I shot brake fluid up all over the hood,lol.
quote]

Sounds similar to a story about my first girlfriend however that's for another forums post. LOL

My friend is comming over on friday with a power bleeder and has done that same thing to clense his line with all new fluid and get the job done right. I just want the dag gone brakes to work........

Thanks for the help. Talk to you soon.....off to bed.