The M939 Truck is a
5-ton 6×6 U.S. military heavy truck. Designed in the late 1970s to
replace the M809 series of trucks, it has been in service ever since.
The M939 evolved into its own family of cargo trucks, prime movers,
and recovery vehicles, with about 32,000 in all produced.


U.S. Marine Corps
M923


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 250 855 cu in (14.0 L) naturally aspirated
diesel engine, producing 240 hp (180 kW) at 2100rpm and 685 lbf·ft
(929 N·m) at 1500rpm. 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 diesel engine producing 240 hp (180 kW) at
2100 and 745 lbf·ft (1,010 N·m) at 1,500 rpm. All models have an
Allison 5 speed automatic transmission with a two speed transfer
case.[5][6]


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. The short, used for tractors and dumps, is 167 in (4,200
mm) / 194 in (4,900 mm), the long ("standard"), used for
cargo and wreckers, is 179 in (4,500 mm) / 206 in (5,200 mm), and the
extra long, used for long cargo and expansible vans, is 215 in (5,500
mm) / 242 in (6,100 mm). (Measurements are from the centerline of the
front axle to the centerline of rear bogie / rear axle).