Truck Features
Ford’s Twin-engined Trucks
Jim Gibson delved into US history and came across a solution to the lack of power in heavy-duty trucks during the late 1930s and early 1940s.
In 1939, a Detroit, Michigan company, Grico, attempted to solve the power problem in trucks in an innovative way, by fitting a pair of petrol ‘flathead’ V8 engines into a Ford cab-over prime mover.
Of course, modern heavy-duty trucks are all diesel-powered, but mid last century long distance prime movers in the USA were mainly petrol guzzlers.
Apart from the high fuel consumption of petrol-fuelled engines, they lacked horsepower to maintain good road speed across North America’s open plains and couldn’t produce the amount of torque required to climb the Rocky Mountains, without struggling at a snail’s pace in low gear.
GM’s GMC 6-71 two-stroke diesel was introduced in 1938, but, beside being expensive, it also hadn’t clocked up enough miles to prove its reliability and longevity, and hadn’t proved it had superior performance and considerably better fuel economy.
In contrast, Ford’s side-valve V8s were inexpensive and quite ‘torquey’ – in particular the 239 cu in (3.9-litre) Mercury truck engine with 95bhp on tap.
That prompted the Grico Two Axle Drive Company to develop a Ford Mercury twin-engined Ford truck. Grico was a subsidiary of the Gear Grinding Machine Company of Detroit.
Gear Grinding Machine’s leading technical mind was Alfred Rzeppa (pronounced Cheppa), the inventor of the Rzeppa constant-velocity universal joint (used in most modern front-wheel-drive cars today). The Rzeppa joint was just one of the Gear Grinding Machine Company’s many innovations.
One of Grico’s main products was tandem axles for heavy-duty trucks and the Twin-Motor Truck might be considered a logical extension of that business.
The Ford COE prime mover’s original V8 engine, drivetrain, and rear axle were retained, and a second V8 engine, transmission, and driveline combination was installed behind the cab, under a sheet metal housing, driving the second axle in the tandem.
The two powertrains were configured so that either one could be operated individually to drive the truck, or they could be run together, controlled by a single throttle, clutch pedal and shift lever.
The twin engines were accessed by pulling them as a unit out of the front of the tractor. In this photo the two radiators are clearly visible through the grille.
How many Twin-Motor Trucks were produced is not known precisely, but around 100 seems to be the best estimate. However, while it was quite possibly the first, Grico was not the only builder of dual-engine Ford trucks. Manufacturers included Spangler, E&L, Merry-Neville and 46 were made by Thorco Dual Motors, a division of the Thornton Axle Company.
James Wagner, the author of Ford Trucks Since 1905, wrote that Mechanical Handling Systems built the corresponding trailers.
According to Fred Crismon, author of US Military Wheeled Vehicles, these highly specialised vehicles were used during WWII as tractors, to pull 60-feet-long ‘super-trailers’ that carried 34 complete aircraft tail-cone assemblies. Each tail cone was part of the B-24 bomber, of which Ford was one of several builders.
Crimson also noted that each tractor was rated at 10 tons and the trailer was loaded from the top by overhead cranes.
According to contemporary sources, the assemblies were carried between several manufacturing plants, including Willow Run, Michigan; Tulsa, Oklahoma; Fort Worth, Texas; Loudonville, Ohio and Buffalo, New York.
The trucks made around 3800 trips, resulting in the production of 1600 or so bombers.
However, the twin-engine concept didn’t survive, because high-output diesels were gathering market support and only one of these diesel engines was required, to offer sufficient power and economy!
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