Equipment Type

Comfortable ‘T8’ Has the Latest Power Train

MX diesel, 8LL UltraShift make for easy driving, though transmission
changed gears too late to suit our truck editor

July 01, 2011

“Is it yellow enough?” That was my wise-guy remark on approaching this Kenworth T800 parked with six others for a recent customer and press event. Cab and hood were painted Viper Yellow, which KW has been using on some of its demo vehicles. It’s a safe color for anything that might trundle through a work site or pause on a highway, which a dump truck does often.

But aside from its happy hue and the strengths inherent in most KWs, there was much more to this “T8”: It had Paccar’s MX diesel, which went on the market just over a year ago, and it was bolted to an “8LL” UltraShift Plus, a recently added version of Eaton’s Vocational Construction Series automated mechanical transmissions that I hadn’t driven before.

We were near Columbus, Miss., at Paccar’s engine plant, where MXs like this one are now assembled. The plant opened early this year and is ramping up to take over production from another factory in The Netherlands, and to serve the growing market for commercial trucks here. Sales in most segments are booming following the Great Recession, though construction remains slow. When buyers of construction trucks come back big-time, they can consider choices illustrated by this vehicle.

Reports we’ve heard say that the MX is proving to be a strong and economical engine. It now goes in about 25 percent of all Kenworths, representatives said, with similar installations in Peterbilts, made by KW’s sister company under Paccar. The MX’s size, at 12.8 liters, is just right for a heavy vocational truck, and like similar diesels from competitors, it makes healthy horsepower and torque–485 and 1,650, in this case, which is the engine’s biggest rating.

The MX is EPA 2010-legal, so uses urea injection to chemically break down nitrous oxides in its exhaust. The equipment is mounted on the right side, along with the diesel particulate filter, and the small 9-gallon tank for the fluid is also there. Some might find this a bother because the fuel tank is on the left side, but drivers and others responsible for topping off fluids should quickly get used to it. Exhaust gas is so clean that the inside of the stack stays shiny and there’s no odor.

Paccar and Eaton engineers have written software to make the UltraShift Plus and the MX compatible, so the two work well together. Clutch operation was flawless and shifts went smoothly almost every time, and were performed better than I could’ve done if I’d been operating a manual version. As any dump-truckin’ son of a gun knows, an 8LL is a Roadranger, with a Low gear plus eight numbered ratios that the driver normally uses while going through Low and High ranges. There are two additional ratios in Low-Low range, accessed by flipping a blue thumb switch on the shift lever’s knob, and these make it a 10-speed tranny.

The start-out gear is among the operating parameters of the automated 8LL that can be programmed at time of delivery, and should be. This one retained the default settings, explained Kenworth and Eaton people, so its normal starting gear was LL-2nd. If the driver wants to use the lowest ratio, LL-1st, he can use a thumb switch on the paddle-handle selector, which this truck had, or punch it up on the optional keypad selector. He’d usually do this while standing still. But he could attempt it while crawling along, and if it wouldn’t overrev the engine, the tranny’s electronic control module would engage it.

In any UltraShift Plus, clutch actuation and gear- and range changing are done by electro-mechanical servos that are directed by electronic controls. These “talk” to the engine’s controls while monitoring accelerator position, engine and road speed, and other data. Through these, the transmission controls sense how heavy the truck is, how easy or severe the terrain is, and how much the driver is pushing things. It “learns” all these things and adjusts shifting to match the conditions. I can’t say I noticed it adjusting to me, but maybe I’m too crusty to work with.

As soon as I began driving the T8, I noticed that the tranny seemed to be using all gears instead of skip-shifting, which is a feature of other UltraShift Pluses. Skipping gears is a good idea when the truck is empty or it’s accelerating downgrade, when not much power is needed, because it keeps engine revs low. So I was puzzled.

And, the engine revved to 1,900 or 2,000 in every gear before the tranny upshifted, which makes noise and uses more fuel than necessary. If I used a very light foot, it sometimes upshifted at 1,700 or so. I wondered why this thing didn’t short-shift—change gears at lower rpm—and why it didn’t shift progressively, at low revs in low gears, then gradually rev higher in the upper gears, when more power is needed. This would be ideal for the MX diesel, which willingly lugs down to 1,100 rpm and less without shuddering and while making strong torque.

Later, this led to phone conversations with Alan Fennimore, Kenworth’s vocational segment marketing manager; and Ben Karrer, Eaton’s chief engineer for UltraShift transmissions. They explained that there are three modes available with the transmission. The default mode is Performance, which lets the engine rev high to use horsepower instead of torque, which many drivers of vocational trucks prefer. That’s what this KW had. There are also Standard and Economy modes, which upshift at 150 to 300 rpm less. An operator wanting lower-speed upshifts should have the dealer program the controls to the appropriate mode.

The automated 8LL doesn’t skip shift because its ratios are comparatively wide-spread, Karrer said. Skipping gears could cause the engine to bog, as it would with a manual 8LL. The UltraShift Plus that I had observed skip-shifting a couple of years ago probably was a close-ratio 18-speed, he said. More ratios mean more opportunity to skip over them. Progressive shifting is not part of current software, but this is in development and test units are with customers.

Not aware of a lot of this during the drive, I went about my business with this KW with some consternation. Then I remembered that the UltraShift can be told what to do by changing the selector to Manual and using the switch on the paddle-handle to direct an up- or downshift. Thumbing the rocker switch upward caused the tranny to shift to the next gear, which I began doing for almost every gear change. And thumbing it downward made the tranny downshift, which I seldom did. (If it’s a keypad selector, punching Manual, then the Up or Down buttons have the same effect.) This is how the engine and transmission should work, I thought.

Anyway, an UltraShift Plus 8LL is made for trucks like this. On this day I cruised up and down nearby U.S. 82 and into downtown Columbus, where I meandered over city streets. At one arterial stop on an upgrade, I used the tranny’s anti-rollback feature, which works with the anti-lock braking system to hold the truck in place. After three seconds it released, as it’s designed to do, so I had to punch the brake pedal again, then get on the accelerator and move through the intersection.

Even though the UltraShift often didn’t behave as I’d have preferred, it still took away a lot of the work of driving and left me free to watch out for other traffic. For novices, not having to learn how to shift a non-synchronized manual transmission will remove a big barrier and let them get on with learning the other skills of dump trucking, such as the proper way to back to a paving machine, spreading stone or gravel, and so on. And they’ll soon be productive and non-destructive to the gearbox and driveline.

And they’ll enjoy driving the truck, something almost guaranteed in a Kenworth. This one was definitely deluxe, with leather-covered seats, power windows and locks, a complete gauge package, and lots of power under the hood from the MX. The ride from the tandem’s modern Hendrickson rubber-spring suspension was fairly smooth, even with a the dump box empty, and the cab was stout and almost air tight. This one had the optional Extended Cab, which adds 6 inches of leg and belly room, something very usable when one doesn’t have to snug close to reach a clutch pedal because there is none.

Now that I understand the transmission and how it can be programmed, I retracted my mumbled complaints and appreciate the opportunity to take it for a spin. As for the yellow paint, sun glasses take care of it, or look at it bare eyed and enjoy it.

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