M939 Truck

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M939 series
US Marine Corps 030224-M-XT622-034 USMC M923 (6X6) 5-ton cargo truck heads a convoy departing Camp Matilda, Kuwait crop.jpg
A United States Marine Corps M923
Overview
Manufacturer AM General[1]
BMY (After 1986 & M939A2)[1]
Production 1982[1]
1989 (M939A2)[1]
Body and chassis
Body style 2-door General Utility Truck[1]
Layout 6x6
Powertrain
Engine Cummins NHC-250 (M939/M939A1)
Cummins 6CTA8.3 (M939A2)
240 hp (180 kW)
Transmission Allison 5 speed automatic
2-speed transfer case
Dimensions
Length 307.4 in (781 cm)
Width 97.5 in (248 cm)
Height 115 in (292 cm)
Curb weight 21,470 lb (9,740 kg)

The M939 series 5-ton 6x6 truck is a family of United States military logistical transportation trucks which was designed in the late 1970s and has been in service ever since.[1] About 32,000 M939 series trucks are in service.[1] The M939 series is an improved version of the older M809 Truck series of trucks.[1]

Specifications[edit]

U.S. Marine Corps M923
M923 Cargo Truck with armored cab

All models of the M939 share a common basic chassis, cab, and hood/fenders. The basic truck is a 6x6 (three axles, six sets of tires, all six 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. [2][3][4]

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[edit]

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 1500rpm. All models have an Allison 5 speed automatic transmission with a two speed transfer case.[5][6]

Tires[edit]

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 centralized tire inflation system (CTIS).

Wheelbases[edit]

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).

Weight of selected models[edit]

Model[7] Type Wheelbase Empty weight Loaded weight[a]
M923 Cargo[b] long 21,470 lb (9,740 kg) 31,470 lb (14,270 kg)
M924 Cargo[c] long 21,470 lb (9,740 kg) 31,470 lb (14,270 kg)
M925 Cargo[b] with winch long 22,750 lb (10,320 kg) 32,750 lb (14,860 kg)
M927 Cargo[d] extra long 24,300 lb (11,000 kg) 34,200 lb (15,500 kg)
M929 Dump without winch short 23,990 lb (10,880 kg) 33,990 lb (15,420 kg)
M931 Tractor without winch short 20,510 lb (9,300 kg)
M934 Expansible van extra long 28,440 lb (12,900 kg) 33,440 lb (15,170 kg)
M936 Medium wrecker long 37,600 lb (17,100 kg) 44,600 lb (20,200 kg)
  1. ^ Cross country load rating.
  2. ^ a b With a 14 ft (4.27 m) dropside bed.
  3. ^ With a 14 ft (4.27 m) bed.
  4. ^ With a 20 ft (6.10 m) bed.

Operators[edit]

Safety[edit]

The safety of the M939 series of trucks has been criticized, especially braking performance and stability when loaded. In 1999 the U.S. Army began refitting anti-lock brake systems to the M939 trucks. Until the trucks were modified, they were limited to a 40 mph (65 km/h) top speed by an Army-wide safety order.[citation needed]

Prior to that improvement, 26% of all Army vehicle accidents and 53% of all Army vehicle accident fatalities were in M939 series trucks. From 1987 to 1998 the series made up 9% of the total U.S. Army vehicle inventory, but accounted for 34% of all fatal accidents.[8]

The problem seemed to be that the torque converter would "lock up" in 2nd gear, and would not unlock easily. When the driver attempted to brake hard, often in a sudden or 'panic' stop, and accidentally locked the brakes (no wheel movement, tires skidding), this would kill the engine; this also killed the power steering, and the driver would suddenly be unable to steer. Too often, the truck would veer sideways and either hit something or roll over.[citation needed].[9]

See also[edit]

References[edit]

  1. ^ a b c d e f g h "M939, General utility truck". military-today. Retrieved 2013-10-12. 
  2. ^ TECHNICAL MANUAL OPERATOR’S MANUAL FOR TRUCK, 5-TON, 6X6, M939, M939A1, AND M939A2 SERIES TRUCKS (DIESEL), U.S. Army TM 9-2320-272-10, Accessed 2006-05-04
  3. ^ Crismon, Fred W. (1998). Modern U.S. Military Vehicles. MBI Publishing. pp. 91–96. ISBN 0-7603-0526-9. 
  4. ^ Doyle, David (2003). Standard catalog of U.S. Military Vehicles. Kraus Publications. pp. 202–203, 205. ISBN 0-87349-508-X. 
  5. ^ Crismon (1998), p. 95.
  6. ^ Doyle (2003), p. 203-204.
  7. ^ Doyle (2003), p. 200-204.
  8. ^ M939 series information page at globalsecurity.org, Accessed 2006-05-04
  9. ^ "Military Safety: Army M939 5-Ton Truck Accident History and Planned Modifications". www.GlobalSecurity.org. US General Accounting Office. Retrieved 23 May 2014. 

External links[edit]