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Paccar reveals 18-speed automated manual transmissions for Peterbilt, Kenworth

Features include 'urge to move' and integrated clutch housing to improve durability

Paccar Inc. revealed new 18-speed transmissions that will go into production in July for Peterbilt and Kenworth heavy-haul trucks. (Photo: Peterbilt)

MARSHALL, Mich. — Paccar Inc.’s new 18-speed automated manual transmissions prove their worth long before approaching a 15-degree hill on Eaton Corp.’s snow-covered proving ground in mid-Michigan.

The TX-18 debuting this July in Peterbilt and Kenworth heavy-haul trucks for on- and off-highway uses doesn’t drive like the family SUV, but maneuverability hauling 140,000 pounds is not that far off a family hauler when it comes to steering feel, braking and a lot of smart assist features Paccar designed to replace Eaton’s 18-speed UltraShift PLUS VXP.

From a hardware standpoint, the TX-18 is a variant of the automated manual transmission joint venture of Eaton and Cummins Inc. called Endurant. But the software, calibrations and integration are all Paccar (NASDAQ: PCAR), so much so that the TX-18 mates only with Paccar’s MX11 and MX13 engines.

The extension to 18 speeds complements Paccar’s TX-12 AMT sibling rated at 110,000 pounds of combined truck and trailer weight. It is now consigned to lighter, less challenging on-highway linehaul. The Paccar TX-8 automatic transmission rated up to 57,000 pounds

The difference between an automatic transmission and an automated manual is the presence of a clutch. But rather than the driver having to guess the proper gear, the AMT does the hunting by controls inside the transmission, barely perceptible step shifting of two or three gears at a time depending on what’s needed.

“It’s always going to feel a little bit different than an automatic transmission, but some of the main benefits are that it’s going to be lighter than an automatic transmission and it’s going to have better fuel economy,” said Kyle Crawford, Peterbilt vocational marketing manager.


The two versions of the TX-18 each put out 510 horsepower and 1,850 pound-feet of torque. The TX-18 is intended for mild vocational use and high performance on the highway. The TX-18 Pro adds six reverse gears, an extreme-duty clutch and performance in severe vocational performance. Think lumber hauling, wreckers, road graders and heavy dump trucks.

Backing up at speed

“The TX-18 Pro really helps in applications where they’re reversing a lot for a long way,” Crawford said. He gave the example of a driver delivering dirt for construction of a single-lane service road where there is no turnaround for the dump truck after delivering its load. Typically the top backing speed is 5 mph. With six reverse gears, the speed can increase to 10 mph.

“So, you’re basically saving 12 minutes reversing back to your pickup point,” Crawford said. “Just imagine how many more loads and how much more productivity and up time you’re going to have.”

And then there is climbing, as in the Eisenhower Memorial Tunnel, about 60 miles west of Denver on Interstate 70, elevation 11,158 feet.

“Just imagine you’re [driving] a manual transmission. You’re in traffic going up a hill, trying to shift back. You’re going to be worn out at the end of the day,” Crawford said. 

This is where the TX-18’s forward-creep, or urge to move, feature comes in. Rather than worrying about the motorist who pulled in a foot behind a driver laden with a 140,000-pound load trying to avoid downshifting to hold his place in traffic, the TX-18 predicts what gear to select based on the incline and estimated load on the truck.

Clutch durability

One of the fastest-wearing parts of a manual or heavy-duty AMT is the clutch. Paccar designed  an integrated clutch housing, replacing 26 bolts used to hold the clutch in place. Each of those, Crawford said, has a potential for leaks or other problems that could require maintenance.

Dual power takeoff units for functions like hydraulic dump trucks put out a combined 160 horsepower, 100 horsepower more than the UltraShift. The PTOs are mounted beneath and behind the transmission.

“Everybody has different needs and different setups,” Crawford said.

On-highway maintenance intervals are 500,000 miles or five years, and vocational intervals are 250,000 miles or three years for the TX-18 and TX-18 Pro. 

Behind the wheel

Kenworth in January provided a literal ride around the block near Paccar’s Sunnyvale, California, technical center in a 52-inch flat roof sleeper cab T880 equipped with the TX-18. Such a short exposure on flat suburban streets made it difficult to appreciate the transmission’s capability.

Most noticeable was the absence of a floor shifter, which created significant space for other uses between the driver and passenger seats. In the TX-18, shifting moves to a column stalk.

A Kenworth T880 with the new Paccar Inc,. TX-18 transmission. (Photo: Kenworth)

Later in January, Peterbilt invited a small group of reporters to drive a TX-12 and the TX-18 and TX-18 Pro. Spins around the Eaton (NYSE: ETN) test track demonstrated the smooth feel of practically effortless highway driving. 

The challenge came when the TX-18 had to ascend a 15% grade. The transmission exerted great effort but had no real problem cresting the incline. Paccar’s new digital display — which debuted last year on the redesigned Peterbilt Model 579 and Kenworth T680 flagships — displayed the gear chosen by the transmission up the grade where three modes of braking slowed the truck on the 8% descending grade. 

After a circle at the bottom of the hill, the truck stopped about a third of the way up the 8% grade and let the TX-18’s urge to move do its thing. It was a bit unnerving to experience the forward movement without a foot on the throttle, but after a few more runs, it felt like something that should happen when stuck in traffic on a steep hill.  

Moving to a skid pad to try out the six reverse gears proved that really making the most of multiple backing gears required an experienced trucker.

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Click for more FreightWaves articles by Alan Adler.

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Alan Adler

Alan Adler is an award-winning journalist who worked for The Associated Press and the Detroit Free Press. He also spent two decades in domestic and international media relations and executive communications with General Motors.