Tuesday, May 31, 2022

GMC CCKW 2½-ton 6x6 truck Information

May 31, 2022 Posted By AdseRudita

The GMC CCKW, also known as "Jimmy", or the G-508 by its Ordnance Supply Catalog nr, was a highly successful series of off-road capable, 21⁄2-ton, 6x6 trucks, built in large numbers to a standardized design (from 1941 to 1945) for the U.S. Army, that saw heavy service, predominantly as cargo trucks, in both World War II and the Korean War. The original "Deuce and a Half", it formed the backbone of the famed Red Ball Express that kept Allied armies supplied as they pushed eastward after the Normandy invasion.

The CCKW came in many variants, including open or closed cab, long wheelbase (LWB) CCKW-353 and short (SWB) CCKW-352, and over a score of specialized models, but the bulk were standard, general purpose, cargo models. A large minority were built with a front mounted winch, and one in four of the cabs had a machine-gun mounting ring above the co-drivers position.

Of the almost 2.4 million trucks that the U.S. Army bought between 1939 and December 1945, across all payload weight classes, some 812,000, or just over one third, were 2 1⁄2-ton trucks. GMCs total production of the CCKW and its variants, including the 21⁄2-ton, 6x6, amphibian DUKW, and the 6x4, 5-ton (on-road) CCW-353, amounted to some 572,500 units – almost a quarter of the total WW II U.S. truck production, and 70 percent of the total 2 1⁄2-ton trucks. GMCs total of ~550,000 purely 6x6 models, including the DUKW, formed the overwhelming majority of the ~675,000 six by six 2 1⁄2-ton trucks, and came in less than 100,000 shy of the almost 650,000 World War II jeeps. Additionally, GM built over 150,000 units of the CCKWs smaller brother, the 1 1⁄2-ton, 4x4 Chevrolet G506, at the same factory.

The GMC CCKW began to be phased out, once the M35 series trucks were first deployed in the 1950s, but remained in active U.S. service until the mid-1960s. Eventually, the M35 series, originally developed by REO Motors, succeeded the CCKW as the U.S. Armys standard 2 1⁄2-ton, 6x6 cargo truck.

The name CCKW comes from GMC model nomenclature:

In 1939-1940 the US Army Ordnance Corps was developing 2 1⁄2-ton (2,268 kg) load-rated 6×6 tactical trucks that could operate off-road in all weather. General Motors, already supplying modified commercial trucks to the Army, modified the 1939 ACKWX – built for the French Army – into the CCKW. The General Motors design was chosen by the Army and went into production at GMS Yellow Truck and Coach divisions Pontiac, Michigan plant alongside 6×4 CCWs. Later they were also manufactured at GMs St. Louis, Missouri Chevrolet plant.

Sources do not precisely agree on the total numbers of CCKWs built by the end of production in 1945. Ware (2010) lists one single number of 562,750 of CCKW trucks, built across all variants – presumably including the amphibian DUKW. More clearly specified numbers are provided by Sunderlin in Army Motors magazine, and by Jackson, using the numbers found in the 1946 revision of the U.S. militarys Summary Report of Acceptances, Tank-Automotive Materiel. Sunderlin reports a total of 528,829 of 2 1⁄2-ton 6x6 units (excluding the DUKW) produced by GMC — versus a total of 527,168 accepted by the U.S. Army. Jacksons tabulation of the 1946 U.S. acceptances numbers adds up to 524,873 units, excluding the DUKWs and the ACKWX predecessor models. Both of these numbers still include the cab-over engine AFKWX-353 models — leaving a total of some 518,000–519,000 actual CCKW-352 and CCKW-353 units. In addition, GMC serial numbers indicate a production of 23,500 of the same bodied 6x4 CCW models, versus 23,649 units accepted by U.S. ordnance.

In any case, GM / GMC built a total of 2 1⁄2-ton, 6-wheeled trucks that was second only to the WW II “Jeep” — and neither Ford nor Willys individually built as many jeeps during the war.

The CCKW was equipped with the GMC 270 engine, an overhead valve inline-6 with 91.5 hp (68.2 kW) or 104 hp (78 kW) at 2750rpm, and 216 pound-feet (293 N⋅m) at 1400rpm. A 3 25⁄32 in (96 mm) bore by 4 in (102 mm) stroke gave a 269.5 cu in (4.4 L) displacement. This (gasoline) engine was designed for commercial trucks, and was reliable in service.

The transmission was a Warner T93 5-speed with a direct 4th gear and overdrive 5th gear. The transfer case had high and low gears, and engaged the front axle. Originally all axles were a Timken split type, later trucks also used GM "banjo" types.

The CCKW had a ladder frame chassis with three driven beam axles, the front on leaf springs, the rear tandem on leaf springs with locating arms. There were two wheelbases, the short Model 352 and the long Model 353. The short, 145 in (368 cm) (Measurements are from the centerline of the front axle to the centerline of rear bogie) was used with a short cargo bed as an artillery prime mover for 75 mm and 105 mm howitzers. All other models used the long 164 in (417 cm) wheelbase. Tires were 7.50-20, brakes were hydraulic with vacuum assist.

Some were fitted with 10,000 lb (4,500 kg) front-mounted winches. A winch added 300 pounds (140 kg) and 14 inches (36 cm).

Some open cab chassis were cut in half behind the cab for air transport. Each half was a load, at the vehicles destination, the halves were bolted back together.

Initially, all versions used a modified commercial closed cab design having a metal roof and doors. By 1944 an open cab version, with a canvas roof and doors, was used. This was easier to build, and the roof could be removed to lower the shipping height. 1 in 4 of cabs had a machine gun mounting ring above the co-drivers position.

The CCKW provided a platform for the widest range of bodies on any U.S. military vehicle, with the 12 ft (3.7 m) cargo version being the most common. As steel was more heavily rationed during the course of the war, the steel cargo bed was replaced by a wooden one. Wooden beds proved unsatisfactory and a composite bed with steel sides, framing, and wooden bottom slats was developed. However, the composite bed was still unsatisfactory and the bed design returned to all steel. Standard cargo models had beds with fixed sides and a drop tailgate, as well as folding troop seats.

A standard rectangular van configuration was used in communications, medical, workshop, and many other specialty roles. Special built vans were also used.

Many specialized variants of the basic 6×6 CCKW were made, some in small numbers, including some converted in the field. These include:

The ACK-353 (A for 1939 design, C for conventional cab, and K for all wheel drive) 1 1⁄2-ton 4x4 truck was the smaller brother of the ACKWX, and a predecessor to the Chevrolet G506, competing with theDodge / Fargo T-203 / VF-400 series, as GM was at that time also trying to clinch the lucrative contract for the standard World War II cargo trucks in the 1 1⁄2-ton 4x4 category.

The ACK-353 was equipped with the new for 1939 GMC 248 engine, an overhead valve, low-deck inline-six with a 3 23⁄32 in (94 mm) bore and 3 13⁄16 in (97 mm) stroke, resulting in a 248 cu in (4.1 L) displacement, producing 77 brake horsepower (57 kW) (net). Transmission was four-speed manual, combined with a two-speed transfer-case engaging the front axle for all-wheel drive operation.