Eisenhower Pass Exhaust Brake Test
We repeated the exhaust brake test on the westbound descent back to Dillon. Eisenhower averages a 2 percent steeper grade than Davis Dam, and that 2 percent made a big difference in slowing the 14-ton fully burdened rigs (trailer, truck and five adult males).
The finishing order changed, with the Sierra requiring five brake applies, the Ram 12 and the Ford 13.
What happened to the Ram? Before we explain, we’ll note that we had both a GM and a Ram engineer in the cab with us (two of the five passengers) during this testing.
If there’s a glaring weak spot with the High Output Ram, it’s the six-speed automatic transmission. The Cummins’ exhaust brake is willing and able to slow the truck, but it doesn’t seem to have the full cooperation and support of the gearbox. By contrast, this is where the GMC’s Duramax and Allison transmission form a formidable team.
By itself, the Duramax exhaust brake doesn’t feel as strong as the Ram’s, but to make up for this, the exhaust brake and transmission work extraordinarily well together. They’ve been engineered that way from the start. The Duramax and Allison downshifted to as low as 2nd gear while the engine stopped burning diesel and only pumped air at 4,150 rpm to slow the truck. The Ram, however, stubbornly stayed in 3rd gear, from 2,500 to 2,900 rpm, and picked up speed until it was forced to upshift to 4th gear to keep from over-revving. Fourth gear, for all the trucks, allowed speeds to increase over 60 mph, forcing us to apply the brakes. If the Ram could have downshifted to 2nd gear, like the Sierra, we think there would have been far fewer brake applies.
The Ford’s weak exhaust brake is its Achilles heel. It had minimal effect slowing the rig and keeping our driver from getting that “white knuckle” feeling you don’t want while barreling down I-70 at night. Although the Ford’s six-speed transmission did a nice job downshifting from 4th to 3rd gear after the foot brake was applied, the wheel brakes on both truck and trailer suffered as stopping power was turned into heat. At the end of every descent from Eisenhower Pass to Dillon, the F-350’s brakes were literally smoking.
Ford has excellent stopping power on flats, but it needs to step up its game in the mountains to stay even with GM and Ram.