I have 1996 LT 4dr 2wd with 4.3l engine. While driving the other day the parking brake light came on for about 30 seconds or so and the brakes went soft. Once the light went out the brakes went back to normal. Pulled over to check things over and found that the brake fluid reservoir was low. Added fluid and off I went. Once I got home I inspected the brakes and the pads and shoes were in need of replacement, thus the cause of the low fluid.


The brake pedal felt normal the entire drive home. Even drove the car a few days longer before changing the brakes. Pulled the car in the drive one evening and replaced the pads and shoes. I adjusted the back drums to the point they are just making contact to the drum. Tested the parking brake and the pedal is maybe a little higher than mid pedal.


Before putting the wheels on and taking the car off the jack stands I thought I would start the car and check the brake pedal. It went to the floor. What the heck? That wasn't an issue when I pulled in the driveway. Now what? I bled the system on general principle although, I had not tampered with any lines or connections. No change after bleeding the system.


I did a search for troubleshooting a spongy brake pedal and found a post where someone mentioned that if you did not remove the reservoir cap before using the C-clamp on the calipers you could damage the master cylinder. Well, when replacing the pads I did the usually C-clamp procedure to push in the caliper for the new pad. I did not remove the reservoir cap when doing this.


So, thinking that was my problem I went and bought a reman master cylinder. Bled the brake system again and still have the same issue. I blamed the recurrence on the reman master cylinder so, I went and bought a new master cylinder and installed it and bled the brakes yet, a 3rd time. Start the car and still the pedal goes to the floor.


I am kind of at a loss here as to what to do next. I feel pretty certain that after two master cylinders; that's not the issue. DUH! However, I am not sure where to go next. I see no leaks at any of the wheel cylinders or flexible lines. I've run about three quarts of fluid through the system with all the brake bleeding so, if there was leak it should be pretty apparent.


Any advice or hints as to what else to look for would be greatly appreciated. I really don't want to take to a garage if I can keep from it.

 

Is the brake pedal spongy only when the engine is off (i.e. when there is no vacuum for the power brakes) or is it also spongy when driving around?

If the brake fluid got so low to let air into the anti-lock system could there be an issue with air getting into it and your bleeding procedure not being able to get the air out of it?

 

Finally got it sorted out. I went to HF to buy a pneumatic bleeder kit as I have exhausted my wife over the last few days with the manual process. I double checked the wheel cylinders and calipers for leaks. No leaks found. Re-bled the system again. I did appear to get some air from the passenger rear. It took awhile for it to come thru. A lot longer than I would have ever thought, especially after previously bleeding the system multiple times prior to this. Whatever. With patience, I persevered and overcame the issue.