Darn ABS again

[wallus]

I'm working on a 97 Tahoe. The brake pedal suddenly got mushy and went to the floor. The fluid was down about a third so I pulled the wheels to check for leaks and found a wheel cylinder gushing badly. All the friction was changed and the rotors and drums machined too.

I bled all of the air out but could tell before I finished that the pedal was the same!

This is where I would normally change the master cylinder but I did some research and found that the ABS system can cause the same problem.

This is my first time working on an ABS equipped vehicle and I am not sure how to bypass/disable the ABS to test it.

I read about a test that requires you to undo the lines one at a time from the master cylinder and plug the outlet then depress the pedal. If the problem persists during this test then the master cylinder is bad, if not then you should start plugging outlets at the ABS unit. Is this a valid test? What else could I try?

I really don't want to start picking parts using process of elimination!!!

Any help/tips would be appreciated.

Thanks, Wally

[phonedrn8]

same problem on my 01 express van for work cyl in rear brake drum seals gone bad. no brake fluid in system all in rear tires and drums had to use emer brake to stop to get to the service shop