proportioning valve??

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adriver said:
The more I read Inline’s explaination, the more confused I get.
What they call a distribution block (250 on the right), I’ve always called a proportioning valve.
Regardless.
I’ve taken several of the ones on the right apart (250). I can’t really can’t tell how that switch works.
It’s got a flush Philips head on the body. That’s all I can see.
Otherwise, there doesn’t seem to be much about them to go bad.
It is all brass except for a spring and two little washers.
They usually aren’t bad.
There is an O-ring and a cupped seal on a plunger.
If you take the cupped seal out of the body (bore) WATCH OUT.
It will expand and you will play heck getting it back in.
If anyone does have a rebuild parts source, it would be nice to know.
Click to expand...

Concerning the valves that were used on A-bodies, calling it a proportioning valve is technically incorrect. It is not a proportioning valve, no matter what anybody calls it. Think about it, what does the word proportion mean? It basically means "difference or differential". A proportioning valve regulates/limits/cuts down pressure, however you want to say it to the rear wheels. It does so because vehicles with light rearends or oversized rear brakes will tend to lock up and the back end will come around if you mash the pedal too hard.

What those valves are really is nothing more than a switch valve and distribution block. In fact if you look at the description on Inline's page showing #250 they don't call it a proportioning valve, they call it a distribution block. Some (like #250) also have 2 other circuits. The valve in the top that the line from the rear of the master cyl. screws into is a hold off valve for the front brakes cause disc brakes grap quick. The part in the lower section I'll do my best to explain later.

The switch valve circuit is there only in case something fails in either the back or front brakes. When something fails and that part of the system looses pressure the other side that has pressure forces the plunger over to cut off the supply of brake fluid to the bad side so you don't loose all your brake fluid. In doing so it allows the good side to still function. In addition to that the plunger contacts the switch to turn on the "brake" like on the dash to warn you something is wrong.

I'm not absolutely positive but I believe the lower section with the O-ring and cupped plunger is a residual pressure valve. It is only needed on a drum brake system (such as the rear wheels). Disc brakes apply more evenly and quicker than drums so an imbalance occurs when the 2 are used unless a residual pressure valve is in the circuit to cause the rear drum brakes to come on quicker. And you are correct about the cupped seal being a bugger to get back in if you take it apart. I wish I knew someone that sold a rebuild kit for it too because I have a valve here that's a good valve but I took it apart to clean it and the cupped seal was so swollen (probably from being in brake fluid all those yrs) I can't get it back in so the valve is nearly useless.

Hopefully that helps :D
 
i am going to take it off sunday run it out to pats
hes had few apart hes says it got dirt or something in it
that car as parked in 1988 outside than in a barn till i bought it
so i will try this
hell i got all winter
and thank u everybody for the help
 
Any Auto parts store 76- 80's dodge truck same as 76 up Duster, Dart. or Volari, Aspen. Looks different because of vender changeafter 73 but works perfect. It is called a proportioning valve for disc. distribution for 4 wheel drum. I believe I have originals used. if I do $50 shipped. correct line ends still installed. I would just cut the lines when remmoved from car to keep out the dirt when stored. Steve
 
this i just pulled from my 72 duster
this had drums all the way around
but now has bbp and disk in the front
my brakelight stays on and pedel feel spongy
i think this is for drums all around
not disk and drum but not %100 sure
i need 1 for 73 up disk brakes
 

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Eddie that one will actually work ok as long as the plunger isn't stuck inside. It doesn't have 2 of the circuits the disc/drum valve has but it will still work, just not quite as good, but it won't cause the problems you are having unless the plunger is stuck. If you take the plug out of the end you can see if the plunger is free. The plunger being stuck will cause the light to stay on but I don't think it'd cause spongey brakes. You may just have air still in the system which would cause both problems. Did you install a new master cylinder? If so did you bench bleed it?

How to bleed the brakes correctly plays a big part in getting all the air out of the system. You should have someone pump up the brakes and starting at the right rear wheel just crack open the bleeder valve quickly then immediately close it. Do this until it doesn't spit at you anymore, just clear fluid comes out. Then do the left rear, then the right front, then left front. Some guys open the bleeder valve too long letting all the fluid run out and it actually lets a little air back in. That's why you should only crack it then immediately tighten it. You don't go through as much brake fluid and make a big mess that way too. Doing it that way you'll get a good hard pedal.
 
Same as my Demon (drum/drum)...now disc/drum with newer style Master and using the BLK250.

The picture is the original (drum/drum) switch I removed:
 

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Now, bleed, starting from the furtherest, and move forward. Never push the pedal to the floor, that will trip the valve. Once half bleed, start over, halfway; guy pushing the pedal can now feel the click, as valve moves. Repeat until air out, if light is on; push pedal-slowly bleed one end of car; click, and light goes out, hold pedal there, tighten bleeder. That wasn't it? same way on other end of car; trying to center the valve, with this.
 
Could you get away with using the stock distribution valve/block on a 68 and just plumbing in an adjustable proportioning valve on the rear line? That way you don't even have to mess with the stock block.
 
mopowers said:
Could you get away with using the stock distribution valve/block on a 68 and just plumbing in an adjustable proportioning valve on the rear line? That way you don't even have to mess with the stock block.
Click to expand...

Yes, and many have done exactly that
 
No, the drum block is a distribution block which contains a piston to operate the pressure warning switch. I'm sure that as old as some of these are, there is a possibility that the piston/ seals can get gummed up and plug up the flow.
 
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