Brake Warning Light On

autotran77 · February 3, 2009

I have a problem with a 79 Chevy 4x4 1/2 ton. The dash 'brake light' now comes on sometimes. I know that it plugs into the proportioning valve. The parking brake does not appear to be stuck on. I have tested the connector that goes into the proportioning valve (it lights when it is grounded).

Sometimes the pedal does go to the floor and seems to be happening more. I never had the brake light come on before when a master cylinder is bad.

My bet would be the master cylinder? Any other ideas?

kuhl_530 · February 3, 2009

It's possible that it could be the master. The light will come on if it detects your e-brake is on, or a brake fault, like low pressure. I had a wheel cylinder blow on my way home from work, and the light went on. I would start with checking the cheapest things first, like break lines, fittings, calipers, and cylinders. If those are not leaking, and are working like they should, it could be a problem with the master or booster.

grosss · February 3, 2009

It's possible that it could be the master. The light will come on if it detects your e-brake is on, or a brake fault, like low pressure. I had a wheel cylinder blow on my way home from work, and the light went on. I would start with checking the cheapest things first, like break lines, fittings, calipers, and cylinders. If those are not leaking, and are working like they should, it could be a problem with the master or booster.

Yup, I made the same mistake with my old truck when I was fixing it up to get it on the road... i replaced the proportioning valve and the master cylinder first before checking the brake cylinders, both of my rear drum cylinders were leaking.

superjim · February 3, 2009

Sometimes the pedal does go to the floor and seems to be happening more. I never had the brake light come on before when a master cylinder is bad.

My bet would be the master cylinder? Any other ideas?

As you probably already know... the brake pedal should NEVER go to the floor.

Unless you have a MAJOR leak and are adding a LOT of fluid to it...it is probably the master cylinder.

DofD · February 3, 2009

The closest I can come to this sort of problem is on the 74 Malibu we had. The rubber air bladder in reservoir lid had a hole in it which caused fluid to leak into it causing a low pressure situation in the brake system, resulting in the brake light coming on and the pedal sometimes going to the floor.

thewaterboy · February 5, 2009

My 79 had a bad master one time and was leaking into the brake booster assembly.....as the leak got worse it started to smoke as the fluid was being sucked into the intake manifold via the booster vac. hose. If all your lines and wheel cylinders and so on look good I'd say check out the master....happy hunting and good luck!!