M39 series 5-ton 6×6 truck
The M39 series 5-ton 6×6 truck (G744) was a family of heavy tactical trucks built for the United States Armed Forces between 1951 and 1969. The basic cargo version was designed to transport a 5-ton, long load over all terrain in all weather. In on-road service the load weight was doubled.
The M39 series was the primary heavy truck of the U.S. Army and U.S. Marine forces during the Vietnam War, and was also used by the U.S. Navy, U.S. Air Force, and ARVN forces.
The M39 series began to be replaced by the M809 series in 1970, followed by the M939 series in 1982, but continues to serve in other nations' armed forces around the world.
History
The M39 series was designed as a 5-ton, three-axle all-wheel-drive off-road truck to replace World War II-era trucks such as 4- and 6-ton 6×6s built by Brockway, Diamond T, Mack, and White. Rushed into production by International Harvester in 1951, soon Kaiser also became a major manufacturer, with Diamond T and Mack building smaller numbers. The M39 series evolved into the M809 (G908) series in 1969, which followed, but did not replace, it. The M809 Series was then improved into the M939 series.Specifications
Engine
The M39 series were originally powered by the Continental R6602, a [Engine displacement|] overhead valve inline 6 cylinder gasoline engine which developed [Horsepower|] at 2800 rpm. The -A1 upgrade had a Mack ENDT-673, a turbocharged inline 6 cylinder diesel engine developing at 2100 rpm. The -A2 upgrade had a Continental LDS-465-1A, a turbocharged inline 6 cylinder multifuel engine developing at 2100 rpm.Gas engine models have a down-swept exhaust exiting from under the body just ahead of the righthand front set of rear wheels. Diesel and multifuel models have a vertical exhaust stack and air cleaner on the right fender; however a very small number of the earliest -A1 models and some -A2 gas/multifuel conversions are seen with same style of downswept exhaust as on gas models.
Of important note, A2's with a factory build date prior 1964 originally were gas engine models. Most of these conversions received the overdrive-5th transmission found in "pure" -A1 and "pure" -A2 models. However, some converts retained their original gas model direct-5th transmission which gave closer gear ratios but a top speed of only 45 mph with a multifuel due to the lower top rpm allowed on that engine compared to a gas engine.
Driveline
All M39s had a Spicer 5-speed manual transmission. Gasoline trucks had a “low” 1st gear and direct 5th. Diesel and multifuel trucks had a different model with a ”low” 1st, direct 4th, and overdrive 5th. A 2-speed transfer case engaged the front axle automatically if the rear axles slipped and moved faster than the front axle. Timken axles were used. Gas models had a 6.44:1 final drive gear ratio except for the M129 C/D, which had a 10.26:1Chassis
The M39 series had a ladder frame with three live beam axles, the front on leaf springs, the rear tandem on leaf springs with locating arms. There were three chassis wheelbases. The M61 short wheelbase chassis, used for tractors and dump trucks, is, the M40 long chassis, used for cargo and wreckers, is, and the M63 extra-long chassis, used for long cargo and expansible vans, is. There was also an M139 heavy duty extra long chassis for extreme service, including the Honest John rocket launcher truck.Many M39 series were equipped with a front-mounted Garwood winch, intended for self-recovery. A winch weighed and added inches to the length of the truck.
The M39 series had both single- and dual-rear-tire models; very few single-rear-tire trucks were built. Most models had 11.00×20s with dual rear tires; tractor wreckers had larger 12.00×20s. Bridge trucks and all M139 chassis-based trucks had 14.00×20s.
A standard military cab, designed by REO, was used. It had hinged doors with roll-up windows, a folding windshield, and a removable canvas roof. A hard roof could be fitted. Cargo trucks and tractors could be fitted with a ring mount for a M2 Browning machine gun.
Models
M54 and M55 cargo truck
The M54 was the standard cargo version of the series. It had a × low-sided box with a bottom-hinged tailgate. Side racks, troop seats, and overhead bows with a canvas cover were standard. A front-mounted winch was optional.The standard body sides could secure a load but could not be loaded from the side by forklifts, so a body with drop sides was standardized as the M54A1C.
The M55, with an extra-long wheelbase, had a box. By contrast, there was no drop-side version of the M814 successor.
M51 dump truck
The M51 was a dump truck used to haul sand, gravel, dirt, rubble, scrap, and other bulk materials. It had a, dump body with cab protector and a tailgate that could hinge at either the top or bottom. They could be equipped with overhead bows, tarpaulin, and troop seats, but the relatively small size of the body limited their passenger or cargo load.M52 tractor truck
Tractor trucks were used to tow semi-trailers up to with on their fifth wheel. Semi-tractor/trailers have to stay on relatively flat ground, and are not rated for full off-road use. On improved roads they could tow up to with on their fifth wheel.Tractor trucks normally towed a 12-ton, 2-axle trailer. There were stake and platform, van, low-bed, and tanker bodies. Six-ton, 2-axle expansible vans and 6-ton, single-axle vans were also used.