brake problem

[howie316]

I am working on a 1995 lumina (car) the wheel cylinder went bad and I lost fluid. I replaced the wheel cylinder and topped off the fluid and bleed the brakes with the car off. As soon as I started the car, I lose pedal. The brakes won't pump up with the car running. When you shut the car off, brakes are fine. Any idea what the problem might be?

[jeffcoslacker]

It feels like that because you have no boost with the motor off...the boost makes the pedal much softer. In reality, the pedal is dead either way, it just feels firmer when not running.

FWD cars use split diagonal braking systems, one chamber of the master cylinder controls one front and one rear brake, the other does the opposing two. When you empty a line, you'll have air in the corresponding diagonal brake...

If you are just bleeding the rear, that's probably the problem.

[howie316]

Thanks for the info, but as I stated, I bleed the brakes! The brakes won't pump up while the car is running. Is my master cylinder bad too? If the master cylinder is bad, should brakes still pump up? Thanks!

[rhandwor]

Did you back off the adjustment to remove the drum. Some times you have to adjust the shoes to get pedal feel. Otherwise I think you still have air in the line. If the master is pumping fluid its probably air. If its not pumping I would suspect it went bad.
I adjust the pads until I can just feel the shoes rub.

[C man]

Also make sure you have adjusted the back brakes properly. I have did this a couple of time before when doing a rear brake job the pedal still feels spongy and I would think that air was still in the system. Each time I eitherforgot to adjust the brakes or I did but not enough. Put on the parking brake and but the car in reverse and give it a little gas. If it moves easily you will have to adjust your brakes some more. Just my prospective though.