Two problems related to brake master cylinder have been reported for the 2003 GMC C2500. The most recently reported issues are listed below.
I was driving down the road when my brake peddle went to the floor, I had to use my emergency brake to stop my vehicle. Luckily I swerved to avoid traffic in front of me and was able to stop safely. Upon having my truck towed, my mechanic showed me that my brake line from my master cylinder had rusted out causing brake failure.
The brakes failed when I tried to stop. The truck was taken a auto repair shop. They told me the brake lines had failed due to rust. The brake lines from the master cylinder and the hydraulic pump had to be replaced. The brake lines from the hydraulic pump and the front wheels had to replaced also.