brake light, mstr cyldr full, dirty fluid in rear resevoir

[1981]

Title says it all,
1981 aotumatic
Brake light is on, brake pedal goes to the floor but front brakes are stopping the car now. Opened the master cylinder: Both sides are full of fluid, front is clear and looks like new fluid, the rear is dirty and blackish. But full! Does this tell me something to help troubleshoot?

Anyone have any ideas where i should start looking first.

Not knowing what could be the problem, I have bled my brakes myself in the past when they had air, but could never get the air out of the system. I always ended up having to pay a shop to pressure bleed them to get the air out.

Oh yeah, any ideas on what I should do first to fix my non-functional emergency braking system? Was riding down the road when the light came on and decided to just "test" the E-brake. Well, pulling the thing all the way and not feeling a bit of stopping resistance kinda scared me. I have no E-brake to help stop me in an E-situation. Not a good time to test this system out and have it fail I guess. It worked in the past, about a year ago.

When I get home I am going to bleed the rear brakes, but I feel this is a lost cause since I have Never had luck in completeing this task on my Vette. But the mechanic that would charge me $50 bucks would with his pressure bleeder. I hate these brakes. 4 discs, 16 pistons, and they are junk. Argh! Help.

Thanks

 

[Bob Chadwick]

It is not normal for the fluid to be blackish. The color indicates that a foreign substance is being introduced into the brake fluid. On a car of this age it could very well be the brake lines deteriorating.

The first thing I would do is to change out the rubber lines that come from the steel lines to the calipers as they are fairly easy to do and readily available. I would then have the brake system flushed.

I haven't had good luck bleeding my brakes either. I have one of those little Mighty-Vac things and have been looking at this bleeder next time I have to do it. About the same cost as one flushing/bleeding. Just make sure you don't suck the system dry.

Then I would go from there.

Does the brake pedal pump up. This can indicate a master cylinder problem.

The light suggests differential pressure between your front and rear brakes. There is a switch in the proportioning valve that grounds and turns on the light when the pressure in unequal.

 

[JohnZ]

The dirty fluid has been fed back from the rear brake system, which indicates that the fluid in the system is OLD; time for a complete flush and bleed of both front and rear systems with new fluid, and the flex hoses should be replaced if they're more than ten years old (they're dated on the outside).

It's not an "emergency brake", and was never designed to stop the car; it's a "parking brake", and was designed to keep the car from moving when parked. There's a two-step process in the Shop Manual that describes the adjustment procedure (shoes first, then the cable system). If that doesn't improve it, it's time for new shoes.