In a heavy duty pickup such as the GMC Sierra, your braking system should be in good working order. Though the GMC Sierra is widely praised for having a stiff, responsive brake pedal, you may need to adjust the pedal height. Depending on the severity of the problem, you may be able to adjust the height yourself in a few minutes.
Get a GMC Sierra owner's manual and check the brake lines for leaks. If the brake lines are still intact and not leaking, proceed with adjusting the pedal height.
Locate the brake booster rod, at the top and rear of the brake pedal lever. It's a thin rod running approximately perpendicular to the lever, with a lock nut at either end. The best way to access it is from the right hand side.
Loosen the adjuster nut, which is closest to the brake pedal lever. If you can't find the appropriate size wrench, an adjustable crescent wrench will work.
Raise the pedal height by twisting the booster rod clockwise, with a pair of pliers. Don't raise it too high, or you may cause further brake problems. To loosen, twist counter clockwise.
Tighten the lock nut. Test your adjustment out. You should have a small amount of free play, but you shouldn't notice any brake chatter or unusual sounds.
Contact a GMC mechanic if your brake pedal remains unresponsive.
