Our final exhaust brake test, this time on the Eisenhower Pass grade, was conducted down the same grade we had just climbed, and it proved to be an interesting competition. We kept many of the parameters of the test similar to what we did during our Davis Dam exhaust brake testing with just a few simple changes. We set all the trailer brake controllers to 7.0 again, knowing there could be some technical variation from one factory brake controller to another (without some type of verifiable certification, that's all we could do).
We targeted 50 mph for our tunnel-exit speed and allowed for a speed range between 40 and 60 mph, much larger than the 10 mph range with the earlier brake test. Since the Eisenhower grade is steeper and shorter, we opted to give each truck more room to work its grade-shifting and exhaust-brake controller software.
Each truck had two passengers and a trailer weighing around 21,000 pounds. As in the Davis Dam brake test, the GMC Sierra 3500's more aggressive and sophisticated exhaust brake was designed to work best with the cruise control to keep the heavy loads in control. So this time we tested each truck with its cruise control on to see if it was smart enough to hold the truck and trailer at the designated speed. Only the GMC held that speed for the full run. Both the Ford F-350 and Ram 3500 just ran away until we touched the brake to slow down; at that point the cruise control was deactivated.
The GMC had the best brake-testing run down the Eisenhower grade with cruise control set at 50 mph in the tunnel; it never needed a touch of the brake or accelerator during the entire run to the Dillon exit. Top speed never exceeded 53 mph, and it never dipped below 49. Not bad, considering the GMC was running at 95 percent of its gross combined weight rating.
The Ford F-350 came in second, needing only one acceleration touch and one brake touch for the entire grade run, downshifting quickly during our only brake touch down to 3rd gear (at 3,400 rpm) which, in combination with the exhaust brake button lit, was plenty to get us down the hill comfortable, never exceeding 57 mph.
We tested the Ram 3500 in both Full and Auto settings and found, with this combined weight on this particular grade, it took five touches in both settings. Full required zero accelerations and five brake events, while Auto seemed more adaptable and in control, requiring one acceleration and four brake events.
We also took front disc brake temperatures of each truck at the bottom of the hill to determine which pickup had been working harder, and the results are as you might expect: The vehicle with the most brake touches (Ram) had the highest temperatures at 425 degrees; the Ford was next at 419 degrees; and the GMC had the lowest at 315 degrees.
Cars.com photos by Evan Sears