Brake warning light stays on

Discussion in 'General Automotive Tech' started by BuickEstate, Oct 1, 2018.

  1. BuickEstate

    BuickEstate Member

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    The brake light is staying on in my 1988 Buick station wagon. The brake light didn't come on until a hole developed in the brake line. The line has been replaced and the brakes work fine again but the warning light is still on. I removed the sensor from the combination valve and the warning light plunger was free. With the sensor unplugged the light went off. The piston in the combination valve looks like it is not centered, causing the warning light plunger to be pushed in and activating the light. I tried bleeding the brakes from the front wheels (they were bled at the rear after replacing the brake line), but it did not recenter the valve. What is the best way to recenter the piston in the combination valve?

    Thank you for your help
     
  2. Silvertwinkiehobo

    Silvertwinkiehobo "Nothing is foolproof as fools are ingenious."

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    You need a second person, but to recenter the valve, you need to open a rear cylinder valve (the right rear) then have someone stomp the pedal. Once the fluid stops, close the valve, then let up on the pedal. That *should* recenter the valve. It didn't work on my Ranchero because the valve stuck, so I replaced it. Hopefully, you won't have to do that to your wagon.
     
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  3. MAK

    MAK Well-Known Member

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    are you sure the master cylinder is ok? Had the same issue, master cylinder was shot, front passenger brake line leaked, opted to replace ALL the brake lines, and bleeder valves , cost me about $780. it took them over 3 hours to get the brake lines & bleeder valves off my 85 Colony Park. your car is 30 years old so seriously look at the brake system.
     
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  4. joe_padavano

    joe_padavano Well-Known Member

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    ^^^^This. The piston got stuck to one side. If you still have the OEM cast iron combo valve, there is likely rust in the bore. I'd go ahead and replace it with a new brass one. Had exactly this problem in my similar-vintage Custom Cruiser.
     
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  5. Silvertwinkiehobo

    Silvertwinkiehobo "Nothing is foolproof as fools are ingenious."

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    Mine was the cast-iron, and I'm sure it had corroded; however, I had rebuilt one from a '68 Cougar that had a brass-bodied one, that was stuck the same way, as the bore was corroded also. So brass isn't necessarily what drives the repair, but getting a unit with clean bores installed is.
     
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  6. BuickEstate

    BuickEstate Member

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    Thank you for the replies. I will try opening the right rear bleeder screw and stomping on the pedal first. If that doesn't work I will look into getting new parts.
     
  7. Pskalli

    Pskalli Member

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    Open one frontcaliper,this will move the piston back,worked for me
     
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  8. OldFox

    OldFox Curmudgeon

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    It's a two way valve. It shuts off whichever part of the car lost pressure. That being said, some go back into place easily and others sometimes require an hour of dicking around to get it reset.
     
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  9. BuickEstate

    BuickEstate Member

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    I fixed this a couple years later. Tried different things to bleed the brakes and recenter the valve but could not get the light to stay out. I suspected the proportioning valve was bad but didn't really want to mess with it since the brakes worked fine. But the valve recently began spraying fluid out the end so I had to get one. After I replaced it and bled the brakes well, all is good and the light went off.
     

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