Brake Master Cylinder problems of the 2014 GMC Sierra 1500

Drove my vehicle about 15 miles and parked it in a parking lot for about 10 minutes. When I returned and backed out of the parking space the brake pedal would not compress much at all unless I pushed on it with some body weight for leverage and only then the vehicle barely stopped - was travelling at a very low speed but still very hard to stop the vehicle. I tried to pump the brake pedal, then carefully moved the vehicle a couple of times to test the brakes and the condition repeated. I then parked the vehicle and shut off the engine momentarily. The condition persisted when I restarted the vehicle. I started to drive the vehicle slowly and carefully in a loop around the parking lot pumping the brakes a couple times and the pedal finally returned to normal. Had I been on the highway when this condition occurred or had I been towing our 5k-lb trailer the consequences could have been catastrophic. Reading online the issue appears common in gm trucks from 2014 up and the cause was often a failing vacuum pump. I located a copy of a service bulletin published internally by gm discussing the issue and prescribing a repair procedure. The bulletin noted that if engine oil escaped past the seal(s) of the failing vacuum pump replacement of the brake booster, master cylinder, and vacuum line may be required in addition to the pump. Given the appearance of this as a common issue, fear of losing brakes again, and fearing that waiting may necessitate other braking components under the hood needing replacement if the oil seeped through the pump, I promptly replaced the vacuum pump. Following the repair procedure prescribed in the gm bulletin there was no engine oil noted in the vacuum line so no further parts were replaced other than the pump and gasket. Condition has not repeated after replacing pump 1k miles ago. Vehicle had approx. 65k miles when this condition occurred.

I have had problems with my brakes for the last 3 years. I already had by brakes fixed my gm because of a bad squeak when pressing on my brakes. I recently just changed my master cylinder because the brake pedal would get stuck on certain occasions when driving. Sometimes having me to use the emergency brakes. Sometimes I would have the brake pedal all the way down and the truck would still keep moving. It would happen sporadically. Most of the time when I am driving in traffic or through a parking lot.

Tried to stop tuck when parking. Brakes were extremely hard and truck came to a slow stop while I was mashing the breaks with all my might. There was break fluid all around right front tire. Dealership found engine oil in vacuum line of vacuum pump due to valve stuck in pump causing hard brake pedal. Replaced vacuum pump, pipe, brake booster and master cylinder, fluid.

2014 GMC Sierra 1500 denali pick-up truck with 67,900 miles: experienced complete loss of power brakes in stop-n-go traffic situation on highway. Problem started as an rare issue that would correct itself and progressively got worse over a week's time. Issue occurred when in traffic requiring frequent stop-n-go braking. Brake pedal went completely to the floor and stopping distances dramatically increased. Had no way to manually apply the brakes to get them fully engaged. Ultimately forced to shift into neutral and apply parking brake to stop. Subsequently found gm bulletin #pit5361b referring to other customer problems with weak vacuum at brake booster. That problem was confirmed and diagnosed by my automotive professional. Ended up having to replace brake master cylinder, vacuum booster, vacuum pump, vacuum tube/pipe and 2 serpentine belts for a grand total of $1626. 00 in repair work (similar amount to the others I found who experienced this issue). Talked to my GMC dealer who confirmed that this is a recognized issue that hasn't yet risen to the level of a "safety recall". However, I was told "stay tuned" because they wouldn't be surprised if a recall on the power brake system was right around the corner.