Army, Mack Defense mark serial production of M917A3 dumper

September 27, 2021

Tom Berg


M917A3military HDT (heavy duty dump) truck
The cab, hood and powertrain sit high to accommodate M917A3’s transfer case, forward drive shaft and powered steer axle. The military HDT (heavy duty dump) truck is an 8×8 to carry a 27-ton on-road payload and deliver high tractive effort in rough terrain. It’s powered by a 12.8-liter 440-hp Mack MP8 with a six-speed Allison 4500 automatic and Meritor high-capacity axles. GVW is 94,500 pounds. (Photo courtesy Mack Defense.)


Mack Defense and the U.S. Army celebrated serial production of the military’s latest heavy dump truck, or HDT, designated M917A3 and based on Mack’s Granite Class 8 commercial model. The event in Allentown, Pa., occurred last week near a dedicated production line in the builder’s Customer Experience Center. Limited production began in January in Mack’s large Lehigh Valley plant and has since switched to the B line at the customer center.

The Army’s vehicle acquisitions branch so far has ordered 155 HDTs with options for another 528, explained Jack Terefinko, Mack Defense’s project manager for the new model. The original order will be split among the Army’s active, Reserve and National Guard branches. They will replace some of the original M917s that are approaching 50 years of age but are still working. Those were built by AM General and were essentially military-specification trucks. Subsequent A1 and A2 commercial-based versions were built by Freightliner starting in the late 1980s and extending into the 2000s.

The Macks are the first new trucks received by the Army in 12 years, said David Hartzell, Mack Defense’s president. Most of the earlier M917s are three-axle 6x6s, some with lift axles, while the new trucks are all-wheel-drive 8x8s with more carrying capacity and high tractive effort over rough terrain. An A3’s on-road payload capacity is 27 tons, with an off-road, cross-country payload of slightly over half of that.

Stock and military spec on M917A3

The M917A3 is roughly 80% stock Mack Granite and 20% military spec, with extra-heavy-duty tow hooks, lifting eyes, and special paint that’s resistant to chemical and biological agents that could be encountered in warfare. Cabs can be “buttoned up” during such attacks and have power windows for fast closing, plus air conditioning to keep crew members breathing healthy air or just comfortable in hot weather.

Granite steel cabs are used on standard trucks while a blast-resistant armored cab is used in others. Either cab can substitute for another in about 16 man-hours of removal and installation work. Both use stock Granite instrument panels plus radio racks and other specialized equipment. An armored cab weighs 8,000 pounds, four times more than the stock cab, so an armored truck’s payload is reduced accordingly, Terefinko said.

A 440-horsepower Mack MP8 diesel is standard and drives through an Allison 4500 Gen5 automatic transmission. Because military trucks might be operated in areas where low- and ultra-low-sulfur fuel is not available, the engines are exempt from emissions limits. They are electronically controlled and operate on JP8 aviation fuel. Meritor supplies a driver-controlled two-speed transfer case and all four of the driven axles, as well as air disc brakes on front wheels and S-cam drums on rear axles. Hendrickson supplies a modified air-bag rear suspension and flatleaf front springs. The truck’s gross vehicle weight rating is 94,500 pounds.

Main frames use heavy steel rails with full-length C-channel inserts, an option available in Mack’s data book. Crossmembers are placed as they would be in a civilian Granite, Terefinko said during a tour of the production line. It was in a portion of the premises initially used for engineering when erected in the 1970s. The special line employs 40 workers at six workstations, condensed from the 100 in the Lehigh Valley plant about 10 miles away. Components are shipped in by suppliers and are pre-painted dull green or tan, ready for installations. The workers turn out one vehicle per eight-hour shift, adequate for the pace of the Army contract.


The stout, stiff mainframe has double C-channels and heavy crossmembers. Suspensions, axles, wheels and other components have been installed, and this chassis will soon be pushed forward to receive a powertrain and cab and then get a dump body. Mack Defense workers are assembling them on a special line in Allentown, Pa. (Photo courtesy Mack Defense.)

Crysteel 18-foot steel dump bodies of the M917A3 have an 18 cubic yard capacity, and the order is split between standard one-piece swinging tailgates and “material control” gates with four remotely controlled chutes so gravel and crushed rock can be poured in one or more furrows. Bodies are sent to the Allentown plant for installation on chassis, one of the last steps in production.

In the works from May 2018

In May 2018, the Army awarded Mack Defense the contract that could be worth up to $296.4 million over seven years to produce up to 683 standard and armored M917A3 HDTs, the company said. The Army signed an agreement last November to purchase 99 Mack Granite-based HDT’s after completing two years of successful Production Vehicle Testing of 12 vehicles at the U.S. Army’s Aberdeen Test Center in Aberdeen, Md., in accordance with the contract program timeline. Then in March, an additional order of 56 HDTs were placed as part of the 2021 Presidential budget.

Testing included running trucks over severe terrain and through water and thick mud in all kinds of weather, Mack Defense people said. Four trucks with armored cabs and shielded fuel and hydraulic tanks were blown up to be sure the components stayed intact. Nonhardened parts did not, which was expected.

Army officials said they are pleased with the trucks and the builder’s performance during the bidding, production and testing stages, and they are talking with Mack Defense executives about follow-on orders for variants on the M917A3. These would include an 8×8 40-ton rough-terrain crane truck and a 6×4 linehaul tractor. The company has built prototypes of those but must compete with other manufacturers to win any orders.

Terefinko said Mack Defense is a subsidiary of Mack Trucks but is semiautonomous with its own officers and board of directors, a legal standing demanded by the military due to Mack’s ownership by Volvo Group of Sweden. LL

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