The M939 is a 5-ton 6×6 heavy truck of the US military. The cargo versions were designed to carry a 10,000-pound load over any terrain and in any weather. It was designed in the late 1970s to replace the M39 and M809 series, and in all 44,590 were produced.
AM General M939 at a glance
| Makers | AM General (M939 and M939A1), BMY (M939A2) |
|---|---|
| Production | 1982–1991 |
| Total built | 44,590 |
| Class | 5-ton 6×6 heavy truck |
| Payload | 10,000 lb (4,500 kg) |
| Engine, M939 and A1 | Cummins NHC250, 855 cu in (14.0 L), 240 hp |
| Engine, A2 | Cummins 6CTA8.3, 8.3 L turbo, 240 hp and 745 lbf·ft |
| Transmission | Allison MT654CR five-speed automatic |
| Axles | Rockwell-Standard double reduction, 6.44:1 |
| Tyres | 11:00R20 dual rear; 14:00R20 single on A1 and A2 |
| Wheelbases | 13 ft 11 in, 14 ft 11 in, 17 ft 11 in |
| Brakes | air brakes |
| Replaced by | M1083–M1091 Medium Tactical Vehicles, from 1991 |
Based on one source: the English Wikipedia article on the M939 series.
History of the AM General M939
A product improvement of the M809
In the late 1970s the M809 series, based on a 1949 design, was becoming old and mechanically dated, yet 35,000 were still in service. A Product Improvement Package was developed to rebuild and update them. A new cab and hood are the easiest spotting features of the result, but there were many other changes.
Rebuilds and new production
In 1982 AM General, which had built every M809, began rebuilding them into M939 and M939A1 trucks at its South Bend, Indiana plant; 24,100 were rebuilt. A follow-up, the all-new M939A2 series, was produced by Bowen-McLaughlin-York, or BMY, in Marysville, Ohio: 20,490 were built. In 1991 the series was replaced by the all-new M1083–M1091 Medium Tactical Vehicles.
Automatic transmission and tyres
By 1980 fewer soldiers knew how to change gear in a heavy truck, and automatic transmissions had matured, so the M809’s manual was replaced by an Allison MT654CR five-speed automatic. It was easier to drive, shifted better and put less shock through the chassis. The unusual M809 transfer case was replaced by a conventional two-speed unit that could shift between low and high range while moving. M939A1 and A2 trucks went over to larger 14:00R20 tyres with a single wheel each side of the rear axles, and the A2 gained a central tyre inflation system.
Design and features
- Allison automatic: a five-speed automatic made the 5-ton truck much easier for a conscript to drive.
- Two engine generations: the Cummins NHC250 of the M809 carried over, while the A2 got the turbocharged 6CTA8.3.
- Central tyre inflation: fitted to the A2, it let the driver lower pressures off-road and raise them again on the road.
- Commercial air brakes: a standard air-brake system modified for military use replaced the air-over-hydraulic brakes of the M809.
AM General M939 versions
- M923 and M925: standard cargo truck with a 14 ft drop-side body; the M925 has a winch.
- M927 and M928: extra-long wheelbase with a 20 ft cargo box.
- M929 and M930: dump truck with a cab protector.
- M931 and M932: semi-tractor for trailers up to 37,500 lb.
- M934 and M935: expansible van with a slide-out section on each side.
The M939 replaced the M809 series and was itself replaced by the FMTV family. The older M35 and the Hummer H1 are the other well-known AM General vehicles. More are in the AM General collection.
Video: ARMY TRUCK AROUND TOWN- AM GENERAL M923 A1
Video on YouTube.
Sources
- M939 series 5-ton 6×6 truck, English Wikipedia: history, engines, chassis, models
