I have a 96 Blazer, 4dr, 2wd, 4.3 engine. I have searched the forum and have not found an issue that was close enough to mine to try the advice posted.

My issue is the brake pedal feels fine when coming to a stop. Pedal is up where is should be, not sppongy or soft. Once stopped the pedal feels fine except, if you continue to apply pressure with your foot, you can push the pedal to the floor. If you release the pedal and immediately depress the pedal again you can put the pedal on the floor. Once on the floor if you pump the pedal a little it will cause the engine idle to bobble a little.

What I have done so far: I assumed it was the master cylinder so I replaced it. I bench bled the M/C and then bled the wheel cylinders in the following order - RR, LR, RF, LF. I started the car and performed a test to see if could push the pedal to the floor. It went to the floor again! I did buy a reman M/C but, I assume it to be good unless you folks think differently. Seems like it would have worked once before going bad.

What should be my next steps to troubleshoot this issue?

My thoughts: The engine bobble when pumping the brake once it is on the floor is making think it could a vaccuum issue with the booster. Is there a way to test it before buying one?

Thanks in advance for you help. I have used advice from other postings to resolve items with my Blazer in the past. Thank you for that information as well.

Larry

 

What happens if you disconnect the power brake booster vacuum? Plug the vacuum line & try it without power brakes & see what happens. It maybe a bad power brake booster. If it still does it then you have a problem with the M/C, wheel cyls, brake line, etc.
Personally I would never use a reman M/C. New ONLY.

 

A vacuum booster problem is pretty easy to diagnose. If the booster is leaking, you should not have vacuum inside the booster after the engine shuts off. Start the engine and let it run for a bit then shut it down and pull the check valve out of the front of the booster. If you hear air rush in, the booster had vacuum. Now, try it again, but this time, wait a bit after you shut off the engine (a minute or two) and see if it sounds the same.

 

Thank you - swartlkk and 4x4blazerguy for your posts.

I performed the booster test. I haven't driven the car at all today so before starting the car I removed the check valve from the booster. There was vaccuum. I heard the swoosh sound. I started the car and tested again as a control to ensure the same level of vaccuum existed. It appears to be the same.

If I am following the logic in the advice given thus far, this would lead me to look at the - M/C, wheel cylinders and lines for leaks. I will look over the entire system. If there are no obvious leaks I would assume I am back where I started, which is the master cylinder. Are there any flaws in my logic?

Any other advice for next steps or other items to check/test that I have not mentioned?

 

Sure sounds like a MC problem. Especially since you have already bled the lines out.

 

That's what figured. Nothing like doing the work twice. Now, if I can just find that receipt it just might still be under warranty so I won't have to buy it twice. That would just be salt in the wound.

Thanks for your help. Maybe some day I can return the favor.

 

Are you sure that you got the MC bench bled properly? I have seen bad MC's straight out of the box so that isn't out of the question, but you may want to bleed the MC again. You can leave it in the truck and just make up some lines to pour back into the res. I have some around here somewhere that I made up a long time ago, but they don't work on newer MCs due to thread differences.

 

I would agree with bleeding the MC and all of the wheels again before trying to pull and replace the MC. On more than one occasion after opening a brake system I have had to go around the car more than once to get all of the air out of the system.

Also when you bleed the wheel cylinders are you just building pressure, cracking the valve and letting the fluid spray out? I have plastic tubing that I bought at the aquarium shop(its fish tank air pump lines) I put it over the valve, put the other end into a bottle of break fluid and just pump the pedal over and over, as long as the end of the tube stays submerged it will not get air into the system.