hi, my combination valve seems seized inside. the brakes have always been a bit crappy at the rear and now its failed its annual mot test (im in the UK) so ive replaced all shoes & pads, new master cylinder, checked the booster as in manual (engine off, pump three times to stiffer pedal etc) about to install new wheel cylinders and then a good long bleed.

After inspecting everything, i noticed the combination valve front "pin" doesn't move in and out as described in the manual when brakes are depressed. After grabbing it with pliers i managed to work it looser but still no movement on its own. i think the spring behind it must be seized? also i noticed the electrical pin/connector on top was at an angle but doesn't ground to earth to throw the warning light on.

Anyways i cant find a rebuild kit and im told these are discontinued. does anyone know of an aftermarket match for our vans? its got rwal so it'll need to connect with the anti-lock block thing.

if i leave it as it is can i still bleed the brakes and get pressure back (the pedal currently goes to floor)

mines a 1993 ram wagon b250, 5.2 v8, 11" rear drums, RWAL, .

thanks

 

here is the valve, you can see the pin/switch is slightly bent to the left of the image, it was worse but i bent it back a bit thinking that since it wasnt touching ground it must be just bent. but now im not so sure.

 

Also called a proportioning valve, I think you're stuck with OEM Mopar new or used.
Think its part # 52008789 but may want to confirm with a dealership.

 

That's only supposed to move if there is uneven brake line pressure between the front and rear systems.

 

I suspect you'll find out if the valve is working when you go to bleed the rear brakes. Assuming the lines are good and you're putting in new cylinders, if you can't get any fluid out (or barely trickles) then you probably have a bad valve.

Be sure to do slow, steady presses on the brake if doing the manual bleed method (not fast, hard!).

 

this is what my workshop manual says about it... im referring to the pin on the left of my picture. i can push it in and then if i smash the brake it does move back out but i have to then push it back in by hand, making me think there's crud or its seized inside.

 

well, i had another search for the right tools and just been out to buy these.. huzza!
http://www.machinemart.co.uk/shop/pr...nut-wrench-set
still waiting for the cylinders to turn up. So no wim gonna go out and see if i can get the combi-valve off and clean it out in the garage. im hoping it will free up and not need new rings and spring...cos i don't got them!

 

so i took off the combi/prop valve ( twisted off a nut in the process..ouch!)
and here is what was behind the stem, a crusty mess. i pulled the other bits and cleaned them up. I also managed to dissasemble more than it shows in my picture, beyond that crud is a a round plastic plate, a hollow shaft a, a rubber plunger, big spring, little spring and a tiny spring and e-clip.. which was loose! after a lot of head scratching i guessed how it went back together and its now reassembled. sorry theres no pic of that bit. luckily all the rubber parts were intact.

 

heres some images of the valve reassembled ready to go back in. it took a while but i found these images which show how the tiny spring and brass check valve go.

 

found this great writ up which showed me how to pull out the pressure diff valve. (although i just used a screw and it came loose)
https://www.musclecarresearch.com/1979-gm-kh-combo-valve-autopsy