Brake problem

[wtd]

I have a 92 chevy Cavalier with ABS. The car had a blown rear wheel cylinder so I replaced both rear wheel cylinders, new brake shoes on both sides, and new springs. I bled the rear lines and will do the fronts today even though the fronts were just done. I also bled the ABS module as best as I could without a scan tool.

The problem is the brakes feel very firm when the car is not running but when the car is started, the pedal goes all the way to the floor and will not pump up. This is exactly what they did before I found the blown rear cylinder.

Is this a symptom of air still in the lines or ABS module or is this a power brake booster problem?

Thanks for any info.

Wayne

 

[labman]

If the pedal goes down more when the engine comes on, the booster is fine or at least no worse than a vacuum leak losing the stopping reserve. There should be vacuum for a couple of stops if the engine stalls.

I don't understand about not pumping up? If it is spongy, it has air in the line, the only problem bleeding the brakes fixes. Did you adjust the rear brakes after installing new shoes? If not, it could take a while if the self adjusters actually work.

Check the calipers for excess travel. Watch while somebody else starts the car. If the calipers and pistons move more than barely enough to see, you have a problem with the hardware or the pistons.

 

[labman]

On further though, likely the master cylinder is shot. Often crud builds up on the walls beyond the usual area the piston travels. When you had a leak in the rear cylinder, the pedal went to the floor damaging the piston cup. Now, with the booster on, fluid sloshes back and forth past the cup and is never forced out the lines. Stick on a new MC, and bleed it before connecting the ABS.

 

[wtd]

Labman,
thanks for the reply. The brakes don't feel spongy, they just sink all the way to the floor as soon as the car is started. The master cylinder could be shot because we flat towed the car probably five or six miles to my house with no brakes and than another couple of miles later on to my friends house who put the motor in. The car was also driven quite a bit after the motor transplant with the brakes going all the way to the floor. I'm sure damage was done to the master cylinder.

The rear self adjusters are screwed all the way in and the drum slightly drags on the new pads. I don't know if I need to do anymore adjustments on this. I've not yet drove the car since the wheel cylinder replacments since its still up on jack stands. I'm hoping to get to work on it in the next day or so again. Thanks again for your replies and any additional info.

Wayne