Making the grade

Descending Loveland Pass in the Cat C15-powered Freightliner required only selecting the right gear and then alternating between the two Jake Brake power settings. Little or no service brakes were required on the descent once the truck was in the right gear.

To get its test program out of the lab and onto the highway, Freightliner annually puts models from Freightliner and its sister brands Western Star and Sterling through high speeds and some of the continent’s steepest, longest grades and tightest curves. Freightliner invited journalists to join the program this year in a ride from Little America, Wy. to Frisco, Colo., followed by testing up and down Loveland Pass, near Frisco. The exercise showed the vehicles have the grunt and cooling capacity to handle steep grades with ease, while preserving a quiet and comfortable driving environment.

Why test on a mountain pass? “The 14,000-foot altitude at Loveland Pass takes the engines right to the edge of turbo efficiency curves and compression ratios,” says Matt Markstaller, project engineer. “We’re likely to see smoke and a drivability reduction from limited power due to the limited pressures. Engines running under those conditions may also generate more heat due to inefficiency.” As if to prove Markstaller’s point, when the nine trucks started in Frisco on the second morning, the limited compression provided by the high altitude created erratic-sounding combustion until each engine had fired a few times and come up to full idle speed.

All of the trucks were so quiet at cruise that only air intake and exhaust noise – no diesel knock or overhead noises – could be heard inside the cab.

While in the Century Class 120ST, we hit an undulating section of I-80 east of Rock Springs, Wyo., but the front axle air suspension absorbed the harshness. The truck had a 14-liter Detroit Diesel Series 60 delivering 515 peak horsepower and 1,650 pounds-feet of torque driving through a Fuller Ultrashift 10-speed.

A Freightliner Columbia with the 12.7-Liter Series 60 had an exhaust system that reduced Jake brake noise to the point where it was even quieter than when running at full throttle with a load. The Detroit produced 455 peak horsepower and 1,550 pounds-feet of torque, also driving through an Ultrashift 10-speed.

A ride up and down Loveland Pass in a Western Star showed how easily a properly spec’d vehicle – in this case, a 625-hp C15 Caterpillar ACERT engine that produced 2,050 pounds-feet of torque and drove through an 18-speed Fuller transmission – can handle the toughest terrain.

Most of the steep climb occurred easily with the tranny’s main box in the sixth position, alternating between low and high split. Finding the right gear for the slightly less steep descent allowed full speed control with only the Jake Brake, alternating between settings. This vehicle cruised quietly at 70 mph with the engine at about 1,550 rpm.

I spent the final portion of the ride from Little America to Frisco in the Columbia. The 12.7-liter engine provided plenty of hill-climbing grunt while running west of Denver and climbing into the mountains. This was a result of proper gearing, with the engine turning at just over 1,600 rpm at 70 mph in top gear. Cruising on the level produced as much as 7 mpg in instantaneous readings, however.

I rode up and down Loveland Pass in both Detroit-powered Freightliners. In each case, the Ultrashift transmission produced astoundingly quick, clash-free shifts that the most skillful driver would be hard-pressed to equal. Part of the secret to getting such quick shifts on upgrades is the transmission’s internal brake, actuated when the ECM recognizes the truck is climbing. Another impressive aspect of the Ultrashift is the sensitivity and smoothness of its simple, centrifugal clutch, which is not electronically controlled.

While I did not get to witness the Freedomline’s performance in climbing, a ride out of a rest area revealed a quick run through the gears under level conditions. ZF engineer Jim DeVore explained how it manages what he says are the fastest of automated uphill shifts. The ZF disengages the clutch and then brings the transmission input shaft to the right rpm with lightning speed using an internal brake, engages the next gear, then gently engages the clutch. Normal clutch engagement is also extremely smooth, with everything controlled electronically.

Oil and coolant temperatures were within reasonable limits at all times. The combination of robust radiators and oil coolers and intelligent engine de-rate strategies means few worries.

“Our goal is to gain real-world experiences in varied operating conditions,” says Brent McKinney, test shop supervisor. “Nothing substitutes for getting out onto the road.”

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