Words by Mike Levine, Mark Williams and Kent Sundling, Photos by Ian Merritt
Davis Dam Grade Exhaust Brake Test
We didn’t just time the trucks up the grade. We also evaluated their exhaust-brake performance while heading back to Bullhead City with the 19,400-pound trailer pushing these dually HDs on their trips downhill.
An exhaust brake saves on brake and transmission wear by clamping down the engine’s turbo vanes, creating back pressure to engine-brake the truck. It also reduces the potential for brake fade during long descents, increasing downhill safety and overall wheel brake life.
The GMC Sierra and Ram 3500 have push-button-activated exhaust brakes that can work in or out of tow/haul mode, while the Ford F-350’s exhaust brake is enabled only when the truck is in tow/haul. Unlike the Duramax and Cummins, the Ford’s exhaust brake can't be turned off. Cruise control was not used.
Example graph of one of several exhaust brake runs in the Ford F-350 towing 19,400 lbs. (approximately 28,400 lbs. combined weight, including three adult males). Six brake applies can be seen here, immediately after speed peaks exceeded 60 mph. Wheel brakes were applied until speed was reduced to approximately 48 mph, to keep the truck in a narrow band between 50 mph to 60 mph.
At the start, we crested Union Pass westbound and set our speed to 55 mph. Then we waited for gravity to take over and the trucks to exceed 60 mph, at which point we applied the wheel brakes to lower our speed to approximately 48 mph to start the pattern over again. We counted the number of times the wheel brakes were applied. The truck with the fewest brake applies wins.
We’ve always liked the Ram’s exhaust brake, which was designed and engineered by Cummins. During last year’s HD Shootout, we considered it a stronger exhaust brake than the one recently added to the Duramax. That belief proved itself on the downhill run from the top of Highway 68. As measured for the trucks' best downhill runs, we had to apply the Ram’s wheel brakes only twice to keep the Ram one-ton in the 50 mph to 60 mph range. The GMC Sierra 3500 required four brake applies, and the Ford F-350 required five.