I have an 81' Camaro and need to know what makes the brake warning light come on?

Last year I had it come on, brakes felt like crap, really didn't slow car down all that well, no matter how hard I push i could not get them to lock up. This was intermittent, meaning the brake light would come on, brakes feel like crap, and then a day later, brakes would be fine and light would go off. After 2-3 weeks of this they finally went bad all the time and light stays on.

I changed the Master Cylinder and brakes worked flawlessly for about 1 week and then back to red light on and bad brakes. Recently I've tried to bleed system, no significant amount of air bubbles, and no difference so its not air in the system.

Is it possible I got a bad Master Cylinder? Cause it worked fine for a week and then brakes went to hell again. Bad wheel cylinders? Or could it be porportioning valve or vaccum boosteR? Is there anyway to check for either?

Have you checked the hard lines? If one of them has a hole in it and you are losing fluid everytime you push on the brakes. It will cause a spongy pedal and it will go to the floor. THat light can only come on 2 ways. The first is if the parking brake is set, the 2nd is if the fluid is low.

The brakes really aren't spoogy. Its like for the first 1/2-1 inch of travel they feel normal, and then suddenly they hit a wall, and it is impossible to push them down any farther. Its like the complete opposite of spongy!

On my '68 the Brake Warning Light is attached to the combination valve under the MC. When the combination valve piston goes too far in one direction, it grounds the Warning Light connection and the light goes ON. At the same time, either the front or the rear brake system gets cut off. Here is information on how to center the combination valve again:

Brake Troubleshooting (http://www.mpbrakes.com/trouble19.htm)

Now, if this problem keeps coming up, it means that either the front or the rear system has a leak somewhere. You need to trace it down.

Good luck,
Theo.