K-10 brake light on

This is a 72 4X4 which uses a proportioning valve in the brake system. The brake light is on and the rear brakes don't have much of an effect. Is this likely a problem with the proportioning valve or the master cylinder. Yes, there's plenty of fluid and the peddle feels ok.

sounds like the m/c or the rear brakes need bled more, have air in them

or the rear shoes need kicked out more

check to see that the shoes are out at the drums inside them


if they are not close enoguh then they will not come out far enoguh before the front pads clamp onto the rotors and prevent the m/c from depressing any further thus preventing the rears from grabbing hard

air in rear line will do the same thing

master cylinder rear piston seals may be bad as well

good luck

The proportioning valve not only regulates pressure but also acts as a safety valve. If it senses a loss of fluid to either the front or rear brakes it will shuttle in either direction to stop pressure and fluid flow where the loss is. When this happens it turns on the brake light as a warning. Sounds like this is what happened to your K-10.

Thanks for the advice. I did notice that when the brakes are applied the little pin in the front of the proportioning valve moves out a little bit. Anything else I can try to diagnose this issue? I'll take a look at the rear brake pads to make sure they are positioned closely when I get a chance.

I just checked the rear brake pads and they are properly positioned just a few clickes on the star wheel from grabbing....I'm stimied because the brake travel and feel is normal which tell me it isn't a master cylinder problem...What do you all think?

If there are no leaks, replace the proportioning valve.

I replaced the proportioning valve and bled the brakes and no more light. It appears to be fixed. Thanks to all for your help.