"The M939 evolved into its own family of cargo trucks, prime movers, and recovery vehicles, with about 32,000 in all produced.
Specifications
All models of the M939 share a common basic chassis, cab, and hood/fenders. The basic truck is a 6×6 (three axles, six wheels, all of which are powered) medium truck. Early M939s were rebuilds of M809 vehicle chassis by AM General, with a new automatic transmission, cab, and hood/fender. Suffix –A2 are new production by Bowen-McLaughlin-York/BMY with later model Cummins engine. The vehicles have a wide variety of configurations and weights.
Note that the motor and tire specifications, along with other improvements, apply to the A2 versions (and A1 versions) of each base model listed below. There is an M928, an M928A1, and M928A2.
Engine
The M939 and M939A1 models use a Cummins NHC 250, a 855 cu in (14.0 L) naturally aspirated inline 6 cylinder diesel engine developing 240 hp (180 kW) at 2100 rpm and 685 lbf·ft (929 N·m) of torque at 1,500 rpm. This was the standard engine of the M809 series. The M939A2 models use a newer and smaller Cummins 6CTA8.3 504 cu in (8.3 L) turbocharged inline 6 cylinder diesel engine developing 240 hp (180 kW) at 2100 rpm and 745 lbf·ft (1,010 N·m) torque at 1,500 rpm.
All models have an Allison 5 speed automatic transmission with a two speed transfer case. The front axle was engaged in low range.
Tires
The M939 uses 11:00 R20 tires with two tires per side per axle in the rear (rear tandem duals). The M939A1 and M939A2 series use oversized 14:00 R20 tires and rear tandem singles. M939A2 series vehicles use a central tire inflation system (CTIS).
Wheelbases
There are three wheelbases (measurements are from the centerline of the front axle to the centerline of the rear tandem). The short, used for tractors and dumps, is 13 feet 11 inches (4.24 m), the long ("standard"), used for cargo and wreckers, is 14 feet 11 inches (4.55 m), and the extra long, used for long cargo and expansible vans, is 17 feet 11 inches (5.46 m)."
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