Yup. If you're not losing any brake fluid from the reservoir, the lip seals inside the master cylinder are torn and leaking. You have to be careful with the new master cylinder on GM cars. Never push the brake pedal more than half way to the floor. Doing that will trip an internal valve and cause one front brake and the opposite rear one to not work and you won't be able to bleed any fluid and air out. You likely won't even notice the loss of braking ability but only two of the four brakes will be working.
Saturday, June 1st, 2013 AT 9:22 PM