Brake problem-While stopping at a red light after driving down a hill the brake pedal drifted to the floor. The vehicle did stop to a point but it kept moving slightly. My wife drove the H3 to my office just a short distance away.My son drove the car around a parking lot and experienced the same. About 4 hours I drove the car home(15 miles) on highway, stop and go, down hills and there was not a problem with the brakes. I had my service man check out the H3 and after a bit of driving he to found that coming to a stop down an incline the brake pedal drifter to the floor. He felt that ther may be a problem with the master cylinder or the hydrolics as the brake fluid level was fine. Hummer towed the H3 to the nearest dealer about an hour and a half away. They received the car on Thursday and to date they have not been able to find any problem. The H3 was pruchased Nov 2005 and has 13300 miles on it. Any suggestions [/align]

 

Regardless..Insist they replace the Master cylinder...The problem you described is classic for that to be the problem...If they can't find a leaky wheel cylinder, then it has to be the Master Cylinder.