The manual GMC parking brake cable is part of your emergency stopping system that goes largely ignored until it is needed. There are between three and four parking brake cables on all GMC trucks; all of which must be in working condition for this system to be able to operate properly. On most GMC trucks the parking brake cables are connected to the passenger compartment by the means of a small pedal on the far left side on the floor. This is an often used pedal, and the GMC parking brake cables are used to initiate this emergency brake system when the truck is being parked on an incline or decline so it will not roll anywhere. The indication that a parking brake cable is broken is when this pedal has pressure applied to it and the tension is either nonexistent or a snapping sensation is felt. The snap is the cable breaking when pressure is being applied. This is the typical time the cable breaks because when the system is not in use, there is no tension on the cables. When no tension is felt, the front cable is the one in need of being replaced. If the snap is felt but there is still some limited tension then one of the back cables has broken. This partial tension is made by the pull on just one of the rear brake shoes instead of the normal two, one on each side, when the emergency braking system is working properly on your GMC truck. Determine just which of the parking brake cables is broken is simple since the broken cable will be dangling down and in easy view of anyone that is observing the underside of the truck.