My assumption, with respect to the emergency brake, is that it should be adequate to prevent rotation of the rear wheels, without assist from the parking pawl in the tranny. Unfortunately, this was found to be in error when the truck was new (2003). The emergency brake would not hold the truck on a slight uphill grade when parking with my 8,400 lb Airstream trailer. This frequently caused the parking pawl to take part of the load. The GMC tech that inspected the brakes (—-under warranty) reported that the emergency brake was operating properly but that the lack of “holding” power - especially in reverse - was a known design flaw for this particular truck. The truck is rated to tow 14,500 lbs but the emergency brake is apparently incapable of holding much more than the weight of the truck alone. That said, I continued to tow the Airstream for the next ten years, choosing my parking sites carefully to avoid parking upgrade. I also carried a commercial set of wheel chocks, which I would use on occasion, and which I am still using today under the front wheels on Boat ramps. The truck does have two 4wd positions - one of which can be shifted on the fly, and the other which requires stopping and passing the tranny through neutral to engage the “stump-pulling” gear. The ability to shift on the fly is the only feature that makes the 4wd in this truck superior to earlier 4wd trucks, as making a sharp turn on dry pavement will still cause binding. It is not really a full-time 4wd system. The load on the front axle, by scale weight measurements, is over 1,000 lbs greater than on the rear axle with the duals when the truck is not loaded. The idea that more rubber on the road makes for greater traction is generally untrue for a dually when lightly loaded. The simple fact is, the duals share the load and, on slippery ramps or icey roads, they generally have less traction - acting more like big skis. This is why few people use a dually for snowplowing here in New England - unless they have a sander in the bed. The duals will ride up on the snow rather than dig down for traction. The weight differential is the reason why, I currently place the chocks under the front wheels at a boat ramp rather than the rear - i.e., more bang for the buck. If you watch You Tube videos of cars and trucks that have gone in the drink on boat ramps, invariably you’ll see that the rear wheels are still not turning as they drag the vehicle out of the water. Dual wheels, on an algae-covered ramp, can be a serious problem - but if some of the emergency brakes’ holding power can be transferred to the front wheels it would add another factor of safety. That is why I sought to find out just how the 4wd system functioned. Kindly forgive the long-winded dissertation.
