When nearing a stop light at est. 15 mph I stepped on the brake and it was like stepping on a rock. The pedal did not move. I pounded on the pedal and finally had enough brake to stop. There were no warning lights. Afterwards the brakes were good. This was repeated twice more. I took it to a brake shop where they checked all mechanical function and found nothing wrong. They hooked up the computer and found no codes. I took it to a Chevrolet dealer and they could not find any codes. During a test drive the mechanic unhooked the vacuum line and had no vacuum. He found the motor was making vacuum. Back at the shop he said it was probably the vacuum booster. When it was replaced the brakes worked as they always had except when they didn't work. Now that the booster has been replaced I do not know if the problem is fixed since it is a random problem. I will not be able to trust the brakes until at least a month goes by with no problems. The truck has less than 29000 miles on it.

- Puyallup, WA, USA