In 1982 AM General, who built all M809s, began rebuilding M809s into the M939 and M939A1 series at their South Bend, Indiana plant.

Early M939s were rebuilds of M809 vehicle chassis with a new automatic transmission, transfer cases, cab, and hood.

The M809 had an unusual 2-speed transfer case that engaged the front axle automatically, a more modern and conventional model was used.

Single, larger tires in a line (having the same track) work better and get stuck less often on soft ground.

Side racks, troop seats, and overhead bows with a canvas cover were standard.

Side racks and overhead bows with a canvas cover were standard but no troop seats were fitted.

[14] The M929 (M930 w/winch) was a dump truck used to haul sand, gravel, dirt, rubble, scrap, and other bulk materials.

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.

A rotating, telescoping, and elevating hydraulic boom could lift a maximum of 20,000 pounds (9,100 kg).

Although the truck was not meant to carry a load, the boom could support 7,000 pounds (3,200 kg) when towing.

Chains, chocks, block and tackle, oxygen-acetylene torches, and other automotive tools were carried.

The largest was the M945 used to mount the so-called "Bat Wing" body Shop Equipment Organizational Repair Truck Mounted (SEORTM), the Antenna Mast section of Patriot Missile Batteries, and with oversized 14:00 R20 tires as a transporter to carry and launch Improved Ribbon Bridge sections and Bridge Erection Boats.

[24] Until the trucks were modified, they were limited to a 40 mph (65 km/h) top speed by an Army-wide safety order.

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.

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.