Brake warning light issue

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Aug 16, 2022 | 06:52 PM

#16

RedFive_R5

Thread Starter

Mountain Pass

Joined: Feb 2018

Posts: 170

Likes: 23

From: Michigan

Quote:

Originally Posted by Hawkbox

One thing that is not standard but might be useful, I wired in an electric choke to what turned out to be a wire for the brake light in the cab. I believe it was purple and when I had it running the light would stay on no matter what I did. So if someone has fiddled with your wiring you may have a false positive.

Quote:

Originally Posted by FuzzFace2

If I was not clear it is the pressure from the master that pushes the valve over to center it.
The master PSI is a lot higher than the PSI you used for pressure bleeding the system.
Also if that dose not work it could be stuck and like you said it might be best to just replace it but I think I would try the bleeder & pushing the master to see if it will center just for S&G's

He knows it is the brake valve as he pulled the wire to it and it went out.
He just needs to center the valve for it to go out.
Dave ----

Quote:

Originally Posted by Richard Mechling

I had that problem the light was on the dash I checked the fluid level because the cap leaks need a new rubber I found the rear cylinder was low topped it off lights still on I applied the brakes really hard making a panic stop that did not skid the wheels but hit the brakes hard they must have shifted that piston and light went out for good so I would suggest try applying the brakes hard

Quote:

Originally Posted by BigBlue2

On my 6.9l IDI the brake warning light will come on with a low vacuum to the booster. The 6.9 has a separate vacuum pump to provide the vacuum but gas trucks will have vacuum supplied from the intake side of the engine. If you are low on vacuum the light comes on for me. Usually requires replacement of the vacuum pump.

Quote:

Originally Posted by Franklin2

The low vacuum switch on my diesel is mounted on the pass side inner fender.

Thanks for everyone's input. I opened up a rear bleeder with no luck, then did the same with a front one, all while using the power bleeder tool. No luck. At this point I decided to just get a new proportioning valve. They are $58 at JBG. I decided to buy the "valve plunger tool" too which is supposed to help keep the valve centered when bleeding. In hindsight I don't think I needed it with a entire new unit. Here's some pics:

I had enough of draining and flushing the brake lines so I skipped that when replacing the valve. Lost a good amount of brake fluid onto the garage floor but that's OK. Got the valve in there fine, it was a direct replacement. It came with an adapter fitting that I needed and a plug, but I didn't need the plug because I have 4x4. It came with a new type of switch that I had to splice into the existing wiring. The existing wiring had two wires, whereas this new switch used one wire.

Anyways, I got it all hooked up and fittings connected, then I bled the entire system per usual with the power bleeder. Everything looked good with no leaks and no air so I turned the key into ignition and the brake light was still on in the dash. But all I had to do was press the brake pedal down once and the brake light went off. So that's good... I saw the brake light which means the wiring was connected properly and it went off as it should when I pressed the brake. Back in business!

So all that to say, if you try all that I did in the first post and still have a brake warning light, I'd probably just replace the valve at that point.