Diagnosing brake problem

[jonnythan]

I have a 1998 Grand Am SE 2.4L.

The brake pedal on my Grand Am travels all the way to the floor when I push on it with moderate force. I am, obviously, trying to figure out why so that I can fix it.

There are no leaks in the system. I have not had to add brake fluid since I last attempted to bleed the brakes.

The parking brake works well.

I have good pads on both the front and back.

I have bled the brakes. I did about 6-8 cycles on each wheel. I realize now this may not have been enough to completely clear the system, but it seems that it would have probably cleared out any air in the system.

The brakes are not *spongy*. They are more *mushy*.

I suspect the master cylinder may be the cause, and I was prepared to try to replace it, but the attached ABS hydraulic control/gear unit seems to complicate this quite a bit. The GM service manual does not really seem to cover replacing *just* the master cylinder.


Do you have any suggestions on how to further attempt to diagnose the problem or how to replace the master cylinder?

Thanks.

[xeroinfinity]

Well if you looked at a GM manual then it should say what needs done. It's nothing realy that difficult to do either.

So yes I would say if all the air was bled from the system that your master cyl is bad.
Also, look to make sure the mounting bolts are all tight and not leaking air.

[jonnythan]

The service manual doesn't seem to talk about replacing the master cylinder at all. I could be missing something, I guess..

[jonnythan]

I replaced the calipers today because they desperately needed replacing.

No change, but I didn't expect a change.

I did find out that the brake pedal doesn't do much of *anything* until it is pressed in more than halfway.

I still suspect the master cylinder because I can't think of anything. I'd appreciate some tips on getting the master cylinder off this vehicle with ABS.

Thanks.