Spongy braking

ALICIA COVERT

MEMBER
2008 MAZDA 5
4 CYL
FWD
AUTOMATIC
120,000 MILES

Had to put brakes on hard to avoid a deer. Afterwards my braking seemed spongy and had to go down further on the pedal to stop. The master cylinder was what I thought it was. Had it changed at dealership. No change in braking it got worse. Finally the pedal went clear to the floor before it finally grabbed. Master cylinder still fine mechanic says. Now thinking it could be with the "automatic braking system" possibly dump valve. Do not want to throw a lot of money at a dealership mechanic since they are not sure what it is either. Any help is appreciated.

1 Reply

STEVE W.

MECHANIC
13,572 POSTS

I would start with a visual inspection of the rubber brake line areas. Stomping hard on the brakes could be enough to damage the aged fibers that keep the hoses from expanding much. To check either jack it up, pull the tires and watch the lines as someone steps hard on the brakes. If you see any of the lines expand or act like a balloon you have a problem there. Next check the various brake calipers and mounts. I have seen calipers fail and mounts break and allow them to move.

It also could be the brake pedal mount flexing or the mechanic could be correct. Especially if you have never really hit the brakes hard enough for the ABS to activate, the valves could have failed and the brake pressure moving the parts that should not be moving.
Hard to say, but a good scan tool and visual inspection should throw a light on the problem.