“Baby 8” T370 Tackles Heavy Work

Feb. 25, 2016

Most commercial truck builders offer alternatives to their true Class 8 models, and you see one of them here: Kenworth’s T370 conventional, which can do many weighty jobs but for less money up front and in everyday operations. The concept originally involved putting a medium-duty power train in a heavy-duty chassis. For example, in the 1950s and ’60s, tandem rear-axle dump trucks from Ford and General Motors were commonly powered by gasoline engines, but it goes back almost to the start of the automotive industry, when third axles were bolted onto Ford Model T chassis so they could carry more. The idea, of course, has evolved greatly, and today’s medium/heavy-duty trucks are infinitely more capable.

Thanks to its tandem rear axles and wide front tires, this T370 looks very much like a Class 8 truck, and it is, as its gross vehicle weight rating is 58,000 pounds (Class 8 starts at 33,001 pounds). Many in the business call this a “Baby 8,” among other things, but climb into the cab, sit behind the wheel, and fire up the Paccar PX-9 diesel (a private-labeled version of Cummins’ ISL9), and it growls like a big truck should. So there’s nothing baby about it except its lesser capacity (compared to, say, a T800 or T880, which can be outfitted with multiple lift axles), and maybe its compact cab, which is a clue that this truck has its origins in KW’s medium-duty line that goes down to Class 5 (19,500 to 26,000 pounds GVW) and the T170. Going upward, there are T440 and T470 variants.

Kenworth T370 Test Set

Truck: Conventional cab, medium/heavy duty straight truck, BBC 108 in., GVWR 58,000 lb.

Transmission: Allison 3000 RDS 6-speed automatic w/ PTO mount

Front axle: 18,000-lb. Dana Spicer D2000 w/ Sheppard dual power steering gear, on 18,000-lb. taperleaf/shock absorber suspension

Rear axles: 40,000-lb. Dana Spicer DSP41 w/ controlled-slip differentials, on Kenworth AG400L air-ride

Axle ratio: 5.29

Wheelbase: 254 in.

Brakes: Bendix S-cam drums w/ Bendix ABS

Tires & wheels: Front, 315/80R22.5 Michelin XZY-3 on 22.5x9-in. Alcoa aluminum discs; rear, 11R22.5 Michelin XDE-MS on 22.5x8.25-in. Alcoa discs

Body: 4,500-gal. Seneca 5-compartment aluminum fuel tanker

My experience with the subject truck was last summer, at Kenworth’s plant in Chillicothe, Ohio, where executives brought together eight different models for inspection and driving by customers and business media. Those of us holding CDLs took as many heavies as we had time for out onto nearby streets and highways. The T370 with its aluminum tanker body looked interesting and execs pointed out that it had a then-newly available 18,000 to 20,000-pound steer axle, so I made it a point to sample it.

The extra-strong steer axle was an option requested by fuel-oil dealers in the Northeast, who want to haul as much product as possible in a truck with limited length, we were told. The tank body could hold 4,500 gallons among five compartments (four of 1,000 gallons and one of 500), and maximum payload was 42,000 pounds, according to the builder’s plate. Pumping and hose equipment was in a large cabinet at the rear. Imagine this body was built for delivering diesel fuel and other fluids to off-road machinery, or install a dump body, and we’d have a construction truck.

The body was built in Iowa by Seneca Tank, part of Almac Tank International in Quebec. The French Canadian province is where Paccar workers assemble the medium-duty T series (and similar Peterbilt models) in a plant in suburban Montreal. If this truck were destined to work in Canada, its speedometer would be calibrated in kilometers per hour. Those numerals appear in a secondary circle, subordinate to miles-per-hour numbers for use in the U.S.

Aside from the truck’s apparent competence at its intended task, my strongest impression of it was the high-capacity steer axle. With no load in the tank, the 18,000-pound taperleaf suspension was necessarily somewhat stiff. And the wide wheels and tires limited wheel cut and made for a large turning circle. Part of this was placement of the dual steering gear boxes outside the frame; wheel stops had to be set to avoid rubbing tire rubber against them. Wheel feel with the Sheppard gear was rather precise.

With limited turnability, I had to plan my maneuvers on Chillicothe’s city streets, which I purposely chose because streets are where this type of truck would spend a lot of its time. As with similar steer-axle setups on dumps and mixers, I spun the steering wheel early while entering corners, especially right-hand turns, to avoid taking a lot of extra lane space. Maneuverability would be likewise limited on job sites, but drivers know this and sometimes have to compensate with extra up-and-back moves to complete their sharp turns. That would be a chore with a manual transmission, but this truck had an Allison automatic; more on this in a bit.

The rear tandem rode rather well, even with no load, thanks to the Kenworth air-ride suspension. Its capacity was 40,000 pounds; that, along with the high-rated steer axle, can stress the main frame. So this one is extra strong, with 3/8- by 10-3/4-inch main rails and a pair of heavy-duty bolted crossmembers at certain spots, among other things. 

An Allison automatic transmission takes away much of the work of driving any truck, including this one. It was invariably smooth and ably transmitted power and torque to the rear wheels. Notably, it was a medium/heavy-duty 3000 RDS (rugged duty series), which costs thousands of dollars less than a heavy-duty 4000 series tranny that would be required with bigger Paccar engines used in full Class 8 truck models. The 3000 is sufficient with PX-9 diesel ratings, including the one on this truck: 350 horsepower and 1,000 lb.-ft. The Allison had several FuelSense features, including Neutral at Stop, where the tranny switches to Neutral when the truck pauses at stoplights and such. Thus the engine doesn’t use extra fuel to try to overcome resistance and the driver needn’t push hard on the brake pedal to keep the truck from moving. 

The 8.9-liter ISL/PX-9 is a midrange-size heavy-duty diesel with features like replaceable wet liners, roller cam followers, bypass oil filtration, and targeted piston cooling. It was based on the smaller medium-duty ISC8.3, which Cummins dropped several years ago. Kenworth (and Peterbilt) offered the ISC as the PX-8, and also offered the ISL as a red-painted Cummins product. Now it’s the PX-9 in conservative gray paint. This engine has a standard base warranty of 2 years or 250,000 miles, whichever comes first, Kenworth literature says. So its life will approach that of larger engines, yet it costs less and weighs less. KW offers the PX-9 in models as big as the W900S, often built as mixer trucks whose operators like low-weight components.

The cab is built of aluminum members and sheeting to rugged specifications, so it resists damage from vibration and corrosion from road and sea salt. And it includes the iconic and strong piano-hinged doors. It is similar to cabs on KW’s older Class 8 models, like the venerable T800. This cab didn’t have the heavier model’s optional 6-inch rear extension that adds leg and head room. But there’s sufficient fore-and-aft travel to send the seat back against the rear wall, and that should suit drivers who like to stretch their legs. Long-legged operators, though, might feel cramped. Compared to some competitors’ cabs, this one is also a little narrow, but work trucks like this seldom carry passengers.

So, the T370 might be a Baby 8 in concept but set up like this, it’s much closer to a full heavy-duty product. Frugal customers will consider it and similar models as a way to get jobs done at less cost, but still enjoy the basic quality and premium-brand image promised by the KW badge.