If there really is an ABS God out there please let him be listening, and answer. It's the same old story. It all started when the front to rear brake line rusted out and had to be replaced. This was about a year or so ago. Bled the rear brakes in the normal fashion but pedal just wasn't right. In winter at the stop sign my rear tires would still be turning. Have bled the rear numerous times with no new results. This last week I almost took out my Buddies car in his driveway when my front ABS kicked in, pedal went to the floor and no stopping. Opted for his wifes flower garden. So, started at scratch with line from MC to combination valve, then line out of ABS Unit to wheels, then Rrear caliper. NO air. Did both gravity bleed and pedal bleed.
Still same. Good hard pedal when engine off but goes to the floor as soon as engine started. As front brakes work I went to gravel road and stomped on brakes hoping the rear ABS would kick in and cycle. Nada. No rear brakes. Stepped on gas with front brakes ABS'n and kept on going. Tried same with front ABS sensors disconected and still no rear ABS or braking. Went home, jacked up rear of truck and started it up, put in drive and hit the brakes. Pedal down to the floor before the rears slowly stopped. Had son do same and I noticed the pin would pop out at the back of the combination valve when hed stepped on the pedal. So, I release front line pressure while he hit the pedal to trigger the combo valve to kill flow to front. Then did same on rear line to reset valve. Did this twice. It didn't make any difference. No idea what to do next. Have pulled the ABS fuse to ensure fronts don't go ABS'n on me again as they are all I have for stopping power. Not sure what the laws are in Canada but if the problem is the ABS unit I would sure like to bypass it. Just gotta figure out what is going wrong. So, ABS God, if you out there and listening, HELP!!!!!

 

Sounds like there's air in the ABS system. Mine does too.

I'm currently Searching for a "How To" article.... So far, I've come up with this article.

Bleeding ABS Brake Systems

I'm not sure yet which ABS system our Blazers have.

Maybe someone will stop by and enlighten us.

 

My guess is buy a new master cylinder. A possibility is when the brake pedal went to the floor and the piston moved beyond the normal travel area it encountered a corroded area and scored the seals. The thing that really makes me wonder is a solid pedal with the engine not running and to the floor with engine running. Did you ever remove the MC and see if it's leaking out the rear? Also if you pull the check valve out of the brake booster with the engine off was it holding vacuum? And is it "wet" like you've been sucking fluid into the vacuum booster?

 

As a test, pull your ABS fuse. See if it acts different. When my front wheel bearing get too worn, the ABS kicks in at the wrong time. Bad. I pull the ABS fuse to prevent it from happening again. If it behaves, you know it isnt your master or air in the lines.

Good luck.

 

ive checked for a vacuum here, and theres quite a bit, as for being wet, its hard to tell, but it doesnt look like it dry... im going to try to bleed the air out of the MC even though i have not touched it other than removing the caps when bring the pistons back into the calipers on the front...