Three problems related to brake fluid leak have been reported for the 2007 GMC Sierra. The most recently reported issues are listed below.
Noticed a puddle of fluid on the garage floor. Investigated and found it to be brake fluid. The entire reservoir emptied on the floor after a day. I had a hole in one of the brake lines under the drivers side. Looking under the truck all the line were terribly corroded and could break at any time . Taking it to my mechanic next week to replace all the lines. 9/1/2015.
2007 GMC Sierra classic with approximately 54,000 miles was being driven into a garage to have wheels balanced. As the technician applied the brakes entering the garage, the brake lines on the front drivers side of the vehicle ruptured and the brake peddle went to the floor. Brake fluid poured out onto the floor and the brakes became completely unusable. If this had happened a few hours earlier in the day as I was traveling on steep mountain highways in west virginia I have no doubt an accident and probable fatality would have occurred. All recommended maintenance had been performed at the gm dealer where the truck was purchased and no warnings from gm were given that the brake lines were showing any signs of wear or that a complete brake failure like this could happen.
While driving the truck on a residential street, the brakes completely failed when I depressed the brake pedal (it went to the floor) and attempted to stop. I lost all normal braking ability and had to stop by down shifting and applying the emergency brakes. When I got the truck stopped and got out, I found that the brake fluid was pouring out onto the ground. A qualified mechanic inspected the truck and found that the brake lines were rusted through and had ruptured. He went on to tell me that this problem is a frequently occurring know problem with GMC pickup trucks and that GMC refuses to acknowledge the issue.