This is on my '98 C-1500... I know there's air trapped in the ABS but there's another problem I haven't seen mentioned anywhere. I bleed the brakes normally and have decent pedal. Then when I start the engine, the pedal drops almost to the floor, which from what I understand is pretty normal for an ABS system. The weird wrinkle I have is that when the pedal drops, it gets stuck there and the truck will only move if I give it a lot of power. Obviously the brakes are "stuck." I can even hear the discs grabbing. I've read the hacks (using a Proportioning Valve Depressor, jacking it up and "driving" it to fool the ABS, driving on gravel or ice to trigger the ABS, etc.) but I'm afraid to drive it because every time I apply the brakes they get stuck. I have to shut if off and wait, and eventually the pedal comes back up and/or I can lift it up. Then the whole thing starts over. Does anyone happen to know if this is still an ABS problem, or do I have a brake hose or a caliper problem as well? Thanks in advance.

 

I have the SAME exact situation as you with my 1996 C1500. I've replaced the master cylinder, and bled QUARTS of fluid through the system. However, there are times that the brake pedal drops to the floor, and then gets stuck, requiring me to hook my shoe under it to pull it back up. Usually happens if I am at a red light too long or in a restaurant drive through and not paying attention too. I've learned NOT to stand on the brake when starting the truck. Once you pump it a few times it is ok. Of course, this usually happens when I am wearing GOOD shoes, then I scuff or mar the top of my shoe pulling the pedal back up...

Someone else ran into this recently, and what finally resolved it for them was to replace the brake booster. That is next on my list for the 1996 truck, when I have time, as I've done everything else. The truck, being a 1996, has ODB2, and my computer says there are small and large vacuum leaks, and I am suspecting this is part of the issue.

Every troubleshooting guide you read that talks about pedals dropping to the floor blames it on the master cylinder, or air in the system, but I've had it with original and replacement master cylinder, and even after bleeding TONS of air and at least a gallon of fluid through the system. I am going to put my bet on the master cylinder, which is original to the truck.

 

Thanks for your reply. Since I posted I've been throwing parts at it. New master cylinder plus calipers (all AC Delco remans). Did the ABS bleed trick (holding the proportioning valve in during bleeding) but the problem persists. Pedal still sticks half way down and I have to shut the motor off and coax it back up. I'm thinking the ABS module itself is bad but your suggestion that the booster could be bad is a good possibility as it's most likely original. I'll have to look at that. - Jake