Brakes drift to the floor

MADLENEPGH

MEMBER
1997 GMC SONOMA
4.3L
6 CYL
4WD
AUTOMATIC
127,000 MILES

Brakes have been drifting to the floor for the last three weeks or so. When I am at a stop sign I feel like the truck is drifting so I have to apply the brakes even more and they are going down toward the floor. Over a three week period the fluid level was maintained, lines underneath were all checked and no leak found, and master cylinder was suspect and replaced with a new master cylinder. But the brake pedal still drifts to the floor. What do you think?

Thursday, October 19th, 2017 AT 6:07 PM

1 Reply

STEVE W.

MECHANIC
15,276 POSTS

Brake pedal drop only happens with a fluid leak, either external though a bad line/wheel cylinder or caliper seal, or internal through a bad master cylinder or fluid bypass into the booster through the master cylinder.

If you are not losing fluid but the pedal is still dropping you either have a second bad master cylinder or possibly a bad rubber line that is acting like a balloon.

Air in the system would create a mushy pedal.

Was this

answer

helpful?

Yes

No

+1

Thursday, October 19th, 2017 AT 8:18 PM