In this month’s Military Monthly, we’re turning our focus back to the five-ton, 6×6 class of U.S. Armed Forces transport vehicles within the M939 series. This time, it’s the M936 Medium Wrecker. While most variants of the M939 series were configured for cargo and/or troop transport, the M936 was designed for the specific tasks of recovering broken-down or immobilized vehicles and lifting large equipment.
“We once ended up having to change the transfer case out of this one with nothing more than hand tools and ratchet straps,” explained Billy Breiling of Those Military Guys in Rancho Cucamonga, California. The company specializes in the service, repair, customization, and resale of military hardware like this M936. “These trucks still see active duty all over the place and come in a number of variants. This particular one has lockers equipped on all the axles.”
The M936 Wrecker is among a number of variants in the M939 lineup. This 23,000-pound truck rides on the "standard" wheelbase within the three main configurations used, measuring 14 feet and 11 inches. Along with its use for the recovery of immobilized vehicles, the crane was used for removing and replacing engines, power packs, and gun tubes, as well as the loading and unloading of large munitions (such as missiles); and is capable of lifting loads of up to 20,000 pounds.
Those Military Guys also made some big changes to this M936 Wrecker’s drivetrain, ditching the old NHC 250 motor and swapping in one of their favorite motors, the 8.3-liter Cummins turbodiesel, which is paired with a five-speed Allison transmission.
“It has all of the towing capabilities most anyone would ever need – it’s the perfect go-anywhere, do-anything vehicle, and it’s totally capable of being a daily driver, the workhorse around a farm, or a weekend warrior for the dirt, mud, or snow,” Breiling said. Let’s take a closer look at the series of five-ton vehicles that this truck is derived from, and how the M936 fits into the roster.
The M939 series trucks use 11:00 R20 tires with two tires per side per axle in the rear. These particular tires are Michelin XZL rubber measuring 395mm in width. M939 series vehicles with the -A2 suffix also feature a central tire inflation system which allows the operator to change tire pressures from the cab to allow for the adjustment of air pressure in each tire to improve performance on different surfaces.
The United States Army began developing the M39 series five-ton trucks a few years after World War II and began producing that series of vehicles in the early 1950s, expanding the lineup and building this series for the next two decades. By the late 1960s, the aging platform was in need of an update, which ushered in the second iteration of the five-ton trucks, known as the M809 series.
Rapid technological improvements in the 1970s saw a ramped-up timeline for a revision, though, and by the early 1980s, the U.S. military was ready to introduce the third iteration of their five-ton trucks into the mix with the M939 series. A pair of evaluation vehicles were constructed for testing by AM General under the XM939 moniker.
The cab of M939 series trucks provides seating for the driver and two passengers. All models have an Allison five-speed automatic transmission with a two-speed transfer case. The front axle is engaged in low range operation. Although the M939 is capable of a top speed of 65 mph (or roughly 55 mph in wrecker configuration), issues with braking stability while loaded with cargo dictated that the Army would limit its top speed operation to 40 mph until anti-lock braking systems could be retrofitted to the existing trucks in the late 1990s.
In standard hauler form, the M939 employed a fully suspended 6×6 wheel configuration and was powered by a naturally aspirated, Cummins NHC 250 six-cylinder diesel engine that developed 240 horsepower and 685 pound-feet of torque at 1500 rpm, which was coupled to an Allison five-speed automatic transmission with a two-speed transfer case. A sizable vehicle at 9.6 feet high, 8 feet wide and 25.6 feet long, the 23,000-pound truck was still capable of reaching 65 miles per hour. The M939 series trucks had an operational range of 350 miles.
While the A1 iterations of the M939 trucks were equipped with a 14-liter, 855 cubic-inch, naturally aspirated inline six-cylinder Cummins NHC 250 diesel engine (which produced 240 hp and 685 pound-feet of torque), this particular example as received an engine swap for the 8.3-liter Cummins 6CTA8.3 turbodiesel powerplant used on the A2 models, which makes 240 hp at 2100 rpm and 745 lb-ft torque at 1,500 rpm.
Initial production of the M939 ran concurrently with the M809, and early versions of the M939 are essentially refreshed versions of the M809, using the older truck’s underpinnings with a new automatic transmission, cab, and front clip serving as the lion’s share of changes versus its predecessor. In 1981, AM General issued an initial manufacturing contract to produce roughly 11,000 examples of the truck.
Subsequent models that used the –A2 suffix designated a new production series built by Bowen-McLaughlin-York (BMY), which started production in the mid-1980s and would employ a number of improvements over the initial series run.
The M936 wrecker is equipped with winches at the front and rear-rated at rated at 20,000 lb and 45,000 lb, respectively. Shipper brace assemblies support the shipper and boom, while the frame tube underneath has storage space for outriggers when not in use. The outriggers provide additional stability while using the crane, while the boom jacks (those vertical oriented diagonal bars in the center of the image on the right) offer additional stabilization for heavy lifting.
The roster of variants in the M939 has continued to grow over the years of production, and now includes cargo haulers, dump trucks, tractor-trailer haulers, expandable bed trucks, and the wrecker configuration we have here. Although tens of thousands of M939 and M809-variant trucks are still in service today, the Oshkosh-produced Family of Medium Tactical Vehicles (FMTV) series, introduced in the early 1990s, has largely replaced the M39, M809, and M939 5-ton 6×6 as the default modular platform to provide those various roles for the U.S. military moving into the future.
Designed for recovery of disabled or otherwise immobilized vehicles and perform crane operations, the M936A1 and A2 series wreckers feature a crane that is capable of lifting loads of up to 20,000 pounds. The crane can swing 360 degrees, extend a maximum of 18 feet, and elevate 45 degrees, all while removing and replacing engines, power packs, and gun tubes, as well as the loading and unloading of large munitions. Although the truck was not meant to carry a load, the boom can support 7,000 pounds when towing. It also features winches at the front and rear of the vehicle (rated at 20,000 lb front and 45,000 lb rear).
The set of controls used for operating the rear winch (left). These include the directional control lever, the torque control lever (which uses high and low settings depending on load). The controls for the crane are on the driver's side behind the cab (right). Controls include boom, hoist, the crowd control lever - which retracts or extends the boom - and swing lever, which swings the crane assembly toward the right when pulled toward the operator or left when moved away.
Equipped with dual fuel tanks, the M936 wrecker has a cruising range of approximately 400 miles with a towed load, and 500 miles without. While towing, the wrecker is capable of climbing road grades as steep as 25 degrees. As configured, the wrecker has a turning radius of 39 feet.
The wrecker configuration uses what’s considered the standard wheelbase length in the M939 lineup, measuring 14 feet, 11 inches. However, it is only exceeded by the extra long configuration used for oversized cargo and expansible vans, which measures 17 feet, 11 inches. The “short” wheelbase configuration used for dump trucks and tractors, measures 13 feet, 11 inches.
While a number of these M936 wreckers remain in service today, they’re being slowly phased out in favor of its MTVR series counterpart. Designed by Oshkosh Defense, these 6×6 tactical vehicles have been in production since 2001 and feature numerous technological advancements versus the M939 series, including the use of a much more advanced Allison HD 4070P seven-speed automatic transmission, which is coupled to an 11.9-liter Caterpillar inline six-cylinder diesel motor that is capable of delivering 425 horsepower at 1800 rpm and more than 1500 pound-feet of torque at 2100 rpm.