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Username Post: Resetting The Proportioning Valve        (Topic#236261)
Senior Member
Posts: 273

Loc: Manitowoc Wisconsin
Reg: 02-15-02
02-23-10 03:55 AM - Post#1867787    

Ok,some backround, 91 chevy cheyene,1500,2wd.50mph down the highway back wheel decides it doesn't want to go the same place as the rest of the truck.I let the truck drag the rear till it stoped,once stoped,I see the speedo is still reading 10 mph,so I lightly touch the brake no change,shut it off and then put in park.Put in new rear brakes,hardware and drums,now the brake pedal is like a sponge.

I do belive I tripped the prop valve.How do I get it to reset,I also have the rwal system.I have done the reset on a 78,and 84,tried that on this one and no dice,any help would be great.

Next step is bypass!!!

Low priced Genuine GM Auto Parts
Bill K.b 
Senior Member
Posts: 4289

Loc: upstate NY
Reg: 10-24-05
02-23-10 08:58 AM - Post#1867941    
    In response to Oldbuz

You have air in the lines and they need to be bled. Because of the prop valve it's difficult at best to pedal bleed them, a gravity bleed worked for me on my '95 van's rear brakes.

Once the lines are bled and the pedal applied the valve will reset itself, but it can't reset if there's not enough pressure in the brake line. Even with a manual reset it will immediately trip again.
Those who can, do. Those who can't, criticize it on the internet.

1988 G20 van 5.7L - driver.
1993 3500 dually 5.7L NV4500 - tow truck
1991 G20 van - parts truck

Plus cars for swap and sale
&yes, I once tried a frame swap on a 51 Chevy.

Posts: 636

Reg: 09-12-07
02-24-10 06:58 PM - Post#1869000    
    In response to Oldbuz

I had a real hard time getting mine to bleed on my 1990 Chevy also with the rear ABS. I tried pushing the brake pedal, gravity bleeding, Russell speed bleeders, the hand vacuum pump and never had much luck. I had done the brakes on my vehicles for years without this much problem. The proportioning valve was not resetting and most of the problem I think. It seemed like the rear cylinders might have been sucking air back in but I am not sure. To reset the proportioning valve I read that you could take a small sledge hammer and hit the brake pedal, I had about 10-12 inches of travel so it was not a massive hit and it reset. I know some may not like this method but I do not think it could do any damage. It worked for me but I was afraid to try bleeding with the brake pedal because it might trip the valve again so I used the vacuum pump at each wheel and now the brakes are better than ever. BG

Forum Newbie
Posts: 72
Loc: Houston, TX
Reg: 07-05-09
02-24-10 09:03 PM - Post#1869066    
    In response to Oldbuz

Sounds to me like you also have an issue with the isolation/dump valve malfunctioning on the RWAL, which can cause the back brakes to lock up if it is dirty inside. It can cause really erratic behavior with the back brakes, and replacement is easy. You also have a lot of air left in the lines with the spongy condition. MightyVac works great for bleeding, just need to put teflon tape on the threads of the bleeder valves when bleeding so as not to suck in outside air. You will need to purge the old fluid out if changing the isolation/dump valve. The brake controller might be funky too.

1989 C3500
2000 C3500
1971 C10 Cheyenne

Bill K.b 
Senior Member
Posts: 4289

Loc: upstate NY
Reg: 10-24-05
02-25-10 01:01 AM - Post#1869106    
    In response to buster_puno

Right in the manual, the valve requires a certain amount of pressure from whichever side of the system you opened, to reset and turn off the dash light. It's the only way to turn the light off.

I could see plumbing the ABS out, I don't know what good rear ABS does, it's the front I want to keep rolling so I can control the vehicle. Once out, you should be able to gravity bleed it pretty easily.
Those who can, do. Those who can't, criticize it on the internet.

1988 G20 van 5.7L - driver.
1993 3500 dually 5.7L NV4500 - tow truck
1991 G20 van - parts truck

Plus cars for swap and sale
&yes, I once tried a frame swap on a 51 Chevy.

Forum Newbie
Posts: 1

Reg: 08-09-13
08-09-13 03:02 PM - Post#2370790    
    In response to Bill K.b

92 GMC Vandura 2500 here. I tried to flush the brake fluid for the first time yesterday and got the proportioning valve stuck so couldn't bleed the rear, and rear brakes didn't work at all. Brake light on dash red unless wire to proportioning valve unhooked. Tried hitting the brakes hard while driving and with both front wheel bleeder valves open, lots of tapping on the valve. No go.

I went out this morning with the idea of taking the proportioning valve out and getting a new one, but I happened to notice the rubber caps on each end. The one on the front (right in picture) which end seems to be for the rear brakes had a 1/8 inch diameter pin sticking out about 1/4 inch. Lower right in picture, taken after the pin went in.

I pushed that pin in about 20 times while tapping and nothing changed according to an ohmmeter on the valve's wire connector, indicating near zero resistance to ground. I got tired of holding that pin in so I headed off to the garage to make a sheet metal clip for it and on the way I noticed the brake lights on so I took away the brace holding the brake pedal in. When I got back from the shop I noticed that darn pin was no longer sticking out! I jacked up one rear wheel, started the engine in neutral, the wheel turned up to 20 km/h according to the speedo, hit the brake and the red warning light went out - and the wheel stopped! I was able to bleed the rear brakes (slow but steady flow with daughter pressing the pedal). Had to be very careful not to drain the very small fluid reservoir for the rear brakes! Did once and tapped on it for half an hour getting bubbles out. The brakes work and stop the van nicely. It does seem that the rear brakes are not going on first as I think they are supposed to, but hard to tell.

Low priced Genuine GM Auto Parts
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