Allisons Help Drivers And Drivelines

Sept. 28, 2010

If there's any doubt in your mind that an automatic transmission is easier to drive, you should've been on a recent demonstration in the Wild West. Allison Transmission, now part of General Motors Powertrain, showed off its products' ease of operation and money-saving potential to an audience of tough-minded truck operators, and may have made some converts.

Marketers and engineers also explained a realignment of Allison medium- and heavy-duty products. They're now divided into a Highway Series (HS) and a Rugged Duty Series (RDS), and some have been uprated in horsepower and torque.

Mechanically, the four-, five- and six-speed automatics are the same from series to series, with one exception: RDS models have provisions for power take-off gearboxes, so use longer cases with space for standard PTO mounts. There are also some warranty differences; RDS models, which Construction Equipment readers are more likely to use, are covered for two years and unlimited miles. HS products have specified mileage limits.

Historically, Allisons have been "torque limited," so could be matched only with smallish engines. But now the medium-duty 3000 Series is approved for up to 370 horsepower and 1,100 pounds-feet; previous limits were 285 hp and 800 lbs.-ft. The heavy-duty 4000 Series can take up to 540 hp and 1,590 lbs.-ft.

The site of this demo was the sprawling Nevada Automotive Test Center near Carson City. This privately owned and operated facility can duplicate driving and climate conditions seen all over the world, according to its operators. Engineers and technicians test vehicles and equipment for civilian and military clients.

Feeling the Allison difference

This time we visitors did the testing. Most of the fleet guys were not Allison customers, but a few of them were and they provided some convincing testimony on Allison's behalf.

But first, the fun: The driving courses showed off the claimed smoothness of the Allisons versus manuals and even automated mechanical transmissions, or AMTs. Eaton and ZF Meritor AMTs are becoming popular among truckers, with Eaton AutoShifts working in many construction trucks. Allison, which for many years has had the self-shifting market to itself, has responded with lower prices and promotional demos like this.

The on-highway portion included drag races between pairs of tractor-trailers. In each race, one had a multi-speed manual or AMT with a big-bore Big Power engine and the other an Allison with a smaller, less powerful diesel. The Allisons always won because they send continuous power and torque to the wheels, and their torque converters tend to keep engines at speeds where they perform best.

Certainly you don't want your drivers drag racing. But faster acceleration gets a truck to its destination quicker and maybe hauls more payload in a given time. One extra load per day for a dumper or mixer is a benefit commonly cited by Allison users.

An Allison can be really useful over soft dirt, hard rocks and steep hills because its torque converter eases power into the driveline, and there's no manual clutch to deal with. I drove seven trucks with Allisons on a marked off-road course, which included a paved oval track with stop signs and a series of sometimes-rough trails.

Each truck's acceleration from a dead stop varied from quick to sluggish. For example, the 11-liter Cummins ISM in a Kenworth T800 mixer was surprisingly lively, but a 12.7-liter Detroit Series 60 in a Western Star 4900 dumper strained against the torque converter for 1 to 3 seconds before the truck began moving, then gradually built up speed. Allison reps blamed the Series 60's electronics, but maybe the 'Star's axle gearing was too high.

For comparison, a couple of the demo trucks had Eaton Fuller 11-speed "LL" manuals and a Mack had a Maxitorque 13-speed. These, of course, were much more work to drive. Especially telling was starting from a dead stop on a 30-percent upgrade.

You know the drill with a manual: Shift into an appropriately low gear; ease off the brakes as you let out the clutch pedal, letting the idling engine pick up the load; when you're moving and the clutch is fully engaged, feed some gas. It's easy if you've got some experience, but this hill is too steep to grab another gear, so you're stuck in Low until you're over the top.

Ease of operation

An Allison, though, requires neither thinking nor finesse: Just release the brakes while you stand on the gas, and up you go. The torque converter compensates for higher gearing in 1st, and its fast ratio allows the truck to accelerate. Every Allison truck I drove (and watched) was moving faster than any manual at the top of this hill.

Reverse, too, is faster in an Allison than a manual, and you can get up some speed while backing to a distant paver or pour site. Yes, you can get a Fuller manual into high range while backing, and you can upshift some Maxitorques into high range (I once got a Mack into 6th-Reverse and about 35 mph), but again, you need to know what you're doing.

Going downhill with an Allison can be more dicey, because while you can select and hold 1st or 2nd gear, an Allison won't always stay there. If engine revs jump on the downhill, it'll switch into neutral to prevent the engine from over-speeding. This is the equivalent of declutching with a manual. Using an engine brake or the Allison's optional retarder helps keep rpm and truck speed under better control.

At $8,500, an Allison HD for a Class 8 truck is a pricey option. But it can pay for itself in maintenance and possible fuel savings, Allison reps contended. One displayed some comparative cost numbers, but critiquing by an audience of skeptical managers showed it's a close call. Still, users testified that Allisons save a pile of time and money in driver recruiting and retention, and eliminate much of the grief that goes with dealing with rookies.

Both on- and off-road, even inexperienced drivers can handle an Allison truck with ease, and without much training, two customers testified at a meeting near the day's end. This greatly expands the pool of potential drivers; in some fleets, half the drivers are women, who tend to appreciate a job more and treat their trucks more gently than men.

New drivers of either gender don't have to learn how to double-clutch a manual transmission, which drastically reduces training time and cuts driveline damage, according to Art Wicks of F.O. Day Trucking in Frederick, Md. "And once you get an experienced driver in a truck with an Allison, you can't get him out," he said. It can also extend the careers of old-timers.

"We had a few older guys who had been with us for years, but their knees were giving them problems and they had trouble with the clutch pedal," he said. "They were thinking of getting out of driving and going into something else, but the Allisons solved that problem and they could continue driving."

The Allisons in F.O. Day's Mack dumpers have retarders, which are especially valuable. "We don't use Jake Brakes," Wicks said. "They're illegal where we run because of the noise. The retarders don't make any noise—you can't hear them work—and they are very effective," so save a lot of brake wear.

Roger Davis, whose namesake dump-truck fleet runs out of DeLand, Fla., had to be talked into buying his first Allison, said Jennifer Davis, who helps manage her father's operation. "For two years we kept trying to get dad to buy one but he kept saying, 'No, a real truck has gears and a real trucker shifts gears,'" she related. "But once we got the first one and he saw what it did, that was it... We're ordering them in all our new trucks."

Among other advantages, Allison-equipped trucks don't get stuck in sand like those with manuals. Drive wheels don't churn up sandy soil, either, which has led to new business. "We're hauling lots of sand to beaches for replenishment projects," she said. "The agencies managing them specify that we send only the Allison trucks because they don't tear up the beach. So that's work we now have, and we didn't used to have it."