Solid pedal but light on

mmanter · Jun 16, 2019

So my 1982 C10 had no brake pedal when I bought it. Thought it was just needing bled, so I filled the master cylinder and bled the brakes, and found a leaky brake line. I installed a new line, and re-bled the brakes. I've now got a solid, high pedal but noticed the brake light is still on at the dash. Checked and the parking brake is released.

Anything I should check on the truck? I think I might go ahead and re-bleed the brakes to be sure, but wasn't sure if there might be an issue with the sensor or with the proportioning valve.

Any suggestions are appreciated.

Matt Manter

Daveo91Burb · Jun 17, 2019

So, I’m not 100 percent sure but I think the prop valve on our trucks is actually not a prop valve at all. If it’s like the one on my 76 vette it’s just a sliding piston between the front and rear systems that is meant to monitor equilibrium between the two - if there’s a pressure loss either front or rear the piston will slide to that side and trigger the brake light. And if that does happen it can be hard to get it to go back to the middle. I’m thinking your leaky line could have triggered it and now it’s stuck there. If I’m not mistaken I think the fix can be as simple as stomping on the pedal a few times to get it to go back.

Like I said, I could be completely wrong here - if I am I’m sure others will chime in.

75gmck25 · Jun 17, 2019

You are correct about how the proportioning valve piston moves to one side or the other and triggers the brake light if there is uneven pressure from front to rear. It can be triggered by a leaking wheel cylinder, leaking brake line, or any other issue that affects pressure.

It may stick in the tripped position, but usually resets itself if there is no brake pedal pressure for a short time. I have also seen suggestions to stomp on the brake pedal to bump the pressure and get it to recenter. I've had mine trip during brake bleeding, but it always went off by itself when I was done.

Bruce

Matt69olds · Jun 17, 2019

You may have to “re-center” the switch by opening the other half of the brake system. Or keep switching between the front and rear brakes until you get all the crud that has collected in the switch over the years.

If that doesn’t work, you can try and center it yourself. Have a helper in the drivers seat, with the ignition on, foot hard on the brake pedal. Whatever end of the truck you last bleed, open a bleeder on the other end slightly, as the pedal drops, the instant the light goes out, close the bleeder. If the light comes back on, repeat on the other end of the truck.

Rickf · Jun 17, 2019

Probably not the switch on the e-brake pedal but doesn't hurt to make sure. Is your proportioning valve under the radiator? I thought to reset it you'd push the button in then apply the brakes. Although it's been a while....

mmanter · Jun 17, 2019

I’m not sure but will have to check that out later today. I thought if I drove it I might reset the light by a couple hard stops but as it was not registered I couldn’t drive it much or far. Today I get plates for it so I can try that out later on.

Mobius · Jul 15, 2019

Ever get it figured out? Mine is on, too, and I’m about to dig in to it to figure it out.

mmanter · Jul 15, 2019

Mobius said:
Ever get it figured out? Mine is on, too, and I’m about to dig in to it to figure it out.

I’ve not had a chance to dig back in to it. Pedal felt solid but won’t hold the truck. I’m thinking it’s got more air somewhere. I’m going to do a full flush to purge all old fluid and see what happens

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legopnuematic · Jul 15, 2019

I had mine trip after I did my rear drums (shoes weren't expanded far enough) but stomping on the pedal re centered it. It should make quite a noticeable noise.

73c20jim · Jul 16, 2019

Take out the bulb, he said, ducking and running.

RoryH19 · Jul 16, 2019

I had many of the same issues on my 82 K5. leaking rear wheel cylinders, bad shoes, worn lines, light would stay on... After I fixed all of the obvious problems I tried to recenter my prop valve. It was seized so I ended up replacing. After I installed the new one the light was off. As soon as I hit the brakes the light stayed on. I recentered, light off and tried again. Same thing, light stayed on.
I then changed the master cylinder and no more light. Has been working for 9 months.
Probably should have done that while doing the brake job. Truck had been siting for 14yrs.

Keith Seymore · Jul 16, 2019

...

I agree with the above posts: switch is not centered in the valve, tripping the light (and meaning you are probably only using the front brake system).

Daveo91Burb said:
So, I’m not 100 percent sure but I think the prop valve on our trucks is actually not a prop valve at all.

Incorrect.

The prop valve in '82 would be a full functioning combination valve, including metering, safety switch and proportioning between the front and rear systems.

K

Daveo91Burb · Jul 17, 2019

Keith Seymore said:
...

I agree with the above posts: switch is not centered in the valve, tripping the light (and meaning you are probably only using the front brake system).

Incorrect.

The prop valve in '82 would be a full functioning combination valve, including metering, safety switch and proportioning between the front and rear systems.

K

Agreed - my bad for the error. My experience with prop valves is limited to that in my '76 Corvette, 4 wheel disc brakes so proportioning between front and rear is not necessary. It's just a block of brass with a piston in it that slides if one of the circuits loses pressure. But the diagnostic and mitigation part of my post still seems to apply.

Keith Seymore · Jul 17, 2019

Yup - all good.

I actually cheated, because I have the engineering brake system release charts all the way back to 1969. I can look and see what the meter/split/slope values (and part number) are for that specific part.

K

mmanter · Jul 17, 2019

I'm hoping I can re-bleed the system and get the light to reset. I really don't want to replace various components to fix the issue. Something isn't quite right though. After draining and refilling my transmission the brakes wouldn't hold the truck, unless I stomped on the pedal.

Solid pedal but light on

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