Project "Thumper" began in Sep. "96. We bought a military 2 ˝ ton truck complete with a 30 ton winch.
First we shortened the wheelbase to 117" (the same length as a Chevy short bed), then lifted it with 8"
blocks. A set of springs from a ‘52 Ford 2-ton (don’t tell Dad!) softened the ride. To accommodate a set of
1600-20 Military tires (52" high), we had to make our own wheels. We used four military wheels and four
Daytons. They were cut and welded together to form four wheels, 20x14" wide. We were running the original
cab (1950) and motor. We were very pleased with the performance until the flywheel came off and fractured the
bellhousing. At this point we decided to start over.
For creature comfort, we purchased a ‘79 Chevy Silverado body originally equipped with a diesel engine.
The powerplant required would have to be a cool-running torque machine built to withstand the abuse of off-road/no-road
4-wheeling. We chose the powertrain from a ‘65 GMC road tractor: a V671 Detroit backed with a 5 speed road-ranger
tranny. This feeds a Rockwell transfer case equipped with a Reb. Kit from Memphis Eqpt. Co. This kit enables the
driver to manually dis-engage four-wheel drive. Differentials are Rockwell top-loaders, 2 ˝ ton. A radiator from a
5-ton truck equipped with a 671 Detroit was reworked to accommodate the V671 and the short Chevy clip. Dual flex-fans
from Summit are controlled by an adjustable thermostat. We raised the suspension to 12". The body was mounted
on 8" channel iron. The driveshafts were reworked and tiebolts were made. The motor and tranny were installed
on the new 8" frame. Total lift is 20". A pair of large chains from the frame to the bottom plate of the
tiebolts holds the front end in place (this enables mounting large obstacles). A pair of heavy eyebolts on each end
of the truck are for the unforeseen or uh-ohs. A pair of 3" aluminum straight pipes remove the fumes and smoke
from the nasty 2-stroke supercharged diesel. This motor produces enormous torque at idle (500 ft/lbs): with the
gears engaged the tires slip on gravel each time the cam rolls over. And I did say "roll" as in roller cam!
Steering is by John Deere: the pilot-actuated steering valve came off a combine, the pump from a cottonpicker.
These control a 24x2" cylinder with a 10" stroke. Fluid coupling enables excellent control of the 52"
tires in the woods without steering-wheel shock or jerk. The battery compartment is located under the bed and welded
to the frame. This allows easy access for service. The original brakes were removed and a single
disc brake from a Ford LTD was installed. We positioned the rotor between the transfer case and the rear
driveshaft. This device works great! In fact it will completely lock the rear tires on asphalt. The main
advantage is the brakes stay "high and dry".
The entire project is not yet complete…..
many thanks to all my friends’ free labor and advice. Special thanks to my Dad for all his time, labor,
and advice. I’d also like to thank the girls (Tammy and Mom) for not killing us, as this many-month
adventure took place. As for the cost, it wasn’t stated for the above reasons!!!!
WE’LL SEE YOU IN THE WOODS !!!!
JEFF DEMPSEY, Forney, AL
PS: This machine is not a daily driver! But it’ll pull the doors off Hades!
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