2002 Neon sport. 2.0 Front Disc/rear drum. Fluid level good no leaks. Brake pedal is low to floor. Car will stop but feels like it has lost the power assist. The booster valve checks out OK. The master doesn't feel like it's bypassing. Start car and let run. turn off and attempt to pump down the booster. 3 pumps and the pedal is hard. Start car and pedal goes almost to floor. Back brakes making no noise. Replaced shoes two years ago. Disc pads and rotors fairly new also. stymied here. Any help would be appreciated. Thanks

 

Usually there are only a few things that will cause a low pedal. #1. Master Cylinder. #2. Rear brakes unadjusted. #3. Low brake fluid.

 

Fluid is not low. Haven't pulled the rear wheels yet. (Tomorrow). Car was fine when my daughter drove it home. The next day the pedal was low. No leaks that can be seen. None at the wheels and none at the master cylinder or behind it that I can tell. May just visit the j yard and get a whole assembly and swap it. Tired of this parts replacement therepy car.

 

Can you pump pedal up for a more solid feeling?

 

It will not pump up with the engine running. If I let it run a minute before shutting it off I will have a pedal when I turn the key off If I pump the pedal two or three times. My question is Master cylinder or Booster. pushing slightly on the pedal does not cause the pedal to creep down indicating a bypass in cylinder.

 

you need to bleed the brakes...somewhere there is air.... i replaced a wheel cylinder and had the same problem.... had pedal before i start car, no pedal after i start it.

 

probably the rear brake shoe fell off? Or as others mentioned, you should try bleeding it.
if everything checks out ok, you can isolate the concern by pinching the brake line, and see which one restores the solid pedal.

 

Usually if the master cylinder is bypassing you can pump the pedal back up to feeling solid again before it starts to drop, but you never know.

 

There was no pumping it up. However I pulled the back drums. All was good there and readjusted for pedal hight. That didn't work as I was getting air in the lines somehow. It ended up being the master cylinder. I never seen one act like that before though. Ka sara sara. Thanks for the help people. Next project is to change leaking axle seals in my 32 ford.