2001 silverado hd. i pushed hard on brakes there was a pop like i blew a line but no leaks, pedal went to floor like line blew also. brakes still work but pedal is pushed to the floor to stop. I bled brakes but not better.

Best thing to do is get a vacuum pump and suck each brake line individually keeping an eye on the level in the master cylinder. See if that gets any better. You can borrow one from advanced auto.

neither is bad. The proportioning valve is kicked and they can sometimes be a bear to re center. Here's the best way I've had success doing that. Before you try opening up any more bleeder screws you, 1)top off the brake fluid reservoir, 2) slowly pump the brake pedal, not all the way to the floor and without the engine running but with the key on, about 20 to 30 times. After you do that you very quickly hit the brake pedal very hard but not all the way to the floor. The repeated slow pumping of the pedal will very slowly put pressure into the line, even if it's air it will compress a little at a time and when you jab the pedal that one time at the end it will re-center the valve. Now here's the key. If the brake light is on it should shut off when that valve centers itself. That's when you must bleed the air out but whoever you have helping you tell them not to push the pedal all the way to the floor again or the valve will pop again. Open the bleeder to the caliper that had the blown line and then have them push slowly down on the pedal only half way to the floor and then stop pushing and hold position til you tighten the bleed screw. After you close the bleeder screw they can let up and do it again. If he pushes it to the floor and you hear a click that means the valve kicked again and you need to start over. Time consuming, yes but it works. I hope this makes sense. Sometimes it's hard to relay what I do to words on paper,.
Dale

Hello Patricia,

Have you checked the master brake cylinder reservoir for brake fluid loss?

I don't suspect the master cylinder as you have replaced it... but am more suspect of a leaking brake line or fitting which should have
been discovered when you had the system bled.

The only time I ever had a rear brake problem with a 2500 series Chevrolet was due to seized rear brake caliper guide pins...as your calipers are also new that is not your problem.

If your brake pedal feels spongy and travels to the floor board you have air in the system, a brake fluid leak or a failure in the power steering system, such as a broken hose, broken power steering pump drive belt, or failed pump, would result in a loss of pressure to both the hydro-boost and steering.

Find more information here:

. Hydro Boost Power Assist Systems Operation Diagnosis and Repair

IF there is no external leaks then the master cylinder must have failed

check all brake lines and wheel cylinders for leakage. if no leaks its probably the master cylinder. symtoms are-- pedal will sink to floor when stopping or not. or master cylinder leaks from behind "it", and runs down brake booster. if booster goes bad the pedal will be very hard! good-day !

when you push pedal hard & pedal goes to floor does brake light come on?
assuming brake fluid leval is ok & didnt run empty have you checked for a leak?
pulling all wheels & inspecting brakes,cylinders, calipers,& lines for leaks.
does the pedal pump up & feel ok with engine running?if so there is air in the system
if it does'nt change the way the pedal feels & no leaks are found & brake linings are ok & adjusted
properly than your master cylinder is leaking internally & needs to be replaced

chances are the seal inside the master cylinder is blown (check for leaks before buying bits......)

Unless you really know what you are doing it is best to get a mechanic to repair this. People's lives and safety are at risk and you could be held legally if something went wrong with your repair job. I would not touch it.

Check for fluid leaks and your brakes. If you see no leaks and your brakes are in good shape replace the brake master cylinder and bleed the system. The air you hear is because the pedal went to the floor. If the booster goes bad the pedal will get so hard you can hardly push it at all. I think you will find if this happened suddenly either you have a major leak or the master cylinder went bad.

Valve is chk valve for vacuum. Any recent brake work? May just need brakes replaced.