Car is a 3.8 L 2002 Monte Carlo SS. Brakes hold pressure and pedal is firm with engine off. When I start engine, the pedal immediately goes to the floor. There is no fluid leaks and I have a new master cylinder. My questions about this are: How critical is the vacuum hose attached to the engine from the booster? Where is the location of the main fuse or circuit breaker for the ABS system? Is there a method to make sure the booster check valve is working? I sincerely need any advice quickly from forum members. Thanks so much. Randall B.

 

Can you pump the brakes up after they go to the floor?

How sure are you that the system is properly bled and there is no trapped air? Sounds like trapped air to me. Was the master cylinder bled prior to installation? That could be a problem See this description.

At this point, it is time to prepare the new replacement master cylinder for installation. First, the master cylinder must be "bench bled." This process bleeds the air out of the master cylinder before it is installed. The master cylinder is clamped into a bench vise and filled with clean brake fluid. Bench bleeding kits that consist of hoses and threaded fittings can be purchased at most auto parts stores. Run the hoses back into the master cylinder's reservoir. Activate the cylinder's piston by pushing it all the way forward with a screwdriver (See photo). Watch the fluid as it cycles back into the reservoir. Keep pumping the fluid through until the large bubbles no longer appear in the fluid


The vacuum line from the booster is important. For one your car will run VERY poorly if it has come loose and your brake pedal wont fade, it will just be extremely hard to depress.

 

You probably need to bench bleed the master cylinder..

 

All good advice above, I agree. There may be air trapped in the ABS controller.
One option to bench bleeding...If you know anyone with a GM "Tech 2" or Snap-On "Solus" scan tool there is a special "Automated Bleed" function designed for this very purpose. It pulses the ABS pump solenoids extremely fast to eliminate air (See attached video). One thing the video doesn't show is throughout the process the scan tool prompts you to bleed the brakes at each wheel in proper sequence.

Video: https://www.youtube.com/watch?v=XsaJ6lkWu7c

 

I was wondering what your take would be on this mans situation. I have come to the conclusion from reading your posts you are a savvy trouble shooter. ABS controller? That could be it to? Will have to remember that, it is a rather large area that could trap air. Thanks

 

Thanks Greg, I owe credit for my knowledge to you and many others on this forum.
I have a Tech 2 and recently had to do this procedure after a pressure bleed left me with a soft pedal.
The "Auto Bleed" works well and is fool proof. The Tech 2 walks you through the whole procedure. The process tends to get the system hot and prompts you to allow the system to cool before proceeding. It won't let you go on until it's satisfied. It does a count down on the bleed time, then tells you to close the bleed screw and which wheel to move to next.

 

Everyone, thank you. I have the fittings and hoses to put the fluid back into the master cylinder reservoir as I get air out of the master. I don't have fancy instruments just a pair of hands and sets of wrenches, but in this day and age things are beyond the scope of the home mechanic.

 

I would offer you one more tip. these posts are great and they will most likely solve your issue.
Not long ago a friend asked me if I would tune up his pick up truck? I said I will get back to you? So I checked the youtube to see if some body made a video on it. Found out I didn't want to even mess with it.
The caution was that the Plug may break off and fall into the cylinder head. So the answer was no.
There is a lot of useful info there and sometimes you get the right one. Good luck with your project.

 

You may not have fancy computer tools, but I firmly believe the remainder of that statement is incorrect. I am just a home mechanic myself, I have done repairs on my cars for years with a tool collection of tools and knowledge I built up over years. And for getting trouble codes for the different systems in the car, there are a lot of cheap scan tool solutions.
If that statement were true, autoparts stores would be going out of business, instead they are still doing well. Since the late 90's I have heard people make that same statement and they make that statement to me, knowing I do all my own work and don't turn my cars over to a shop.

Yes, as time goes on, computers in the cars are getting more and more involved. Unless you get to a point that you need a diagnostic tool (like a GM Tech II) to command the car to do something, there is a lot you can still do for yourself. There are some jobs that do require the GM Tech II in order to complete, but far and few for the average car problem. And for diagnostics, the Tech II has some tricks to help, but there are sometimes other ways to get around that.

If you have a want to work on your cars, never give up. Figure out what it is you would actually pay a mechanic to do.

 

Apologies. The words"beyond the scope of the home mechanic" came from all the Haynes books I have. I should have said " beyond the scope of SOME home mechanics" because I'm not going to rest until I get this car on the road. I am thinking the remanufactured master may be junk. Came from Advance auto store. Had brake fluid around the outlets when I opened the box. unless this master was tested. There doesnt seem much pressure coming from the front wheels outlet of the master.