The Toyota BJ is essentially an SB-type chassis mounted with an engine built for a 4-ton truck. It was originally developed in response for a bid from the National Police Reserve Forces, like the Willys Jeep, but there were several significant differences between the two models. One difference was the engine. The Willys Jeep had a 2.2-liter compact in-line 4-cylinder engine mounted in a compact body. By contrast, the Toyota BJ-type vehicle had a 3.4-liter large-sized in-line 6-cylinder engine.
The so-called B-type engine not only had a larger piston displacement, but also structural differences. Build for effectiveness on the battlefield, the Willys Jeep had pursued a low hood profile, and consequently was built with side-valve type cylinder heads. The Toyota BJ-type on the other hand, with its larger piston displacement and cylinder head structure, was better suited to the dawning new age of the 4x4.
There were also differences in the power train. From the BJ-type to the subsequent Land Cruiser 20-series there was no LO gear in the transfer. As a part-time 4x4, the transfer lever extending from the floor only triggered a switch from 2WD to 4WD mode. The 3.4-liter engine had strong torque from the start, so there was no particular need to secure extra torque by means of a complicated subgear in the power train. However, the 4-speed transmission also came with a low gear, the 1st gear having a low gear ratio of 5.53 in the 1st gear compared to the final gear ratio of 4.11, a result of its being based essentially on truck specifications. The low gear ratio in the transmission also limits the maximum speed you can get out of the vehicle, but at the time there were few paved roads, and for a car designed from the start for limited applications this was not a problem.
The National Police Reserve Forces elected to go with the Willys Jeep for their procurement program, but in many respects the Toyota BJ was a superior vehicle. It had a larger piston displacement, a longer wheelbase, and a larger body. Moreover, its softer suspension settings reduced fatigue on the driver, all of which contributed greatly to Toyota's later success in penetrating overseas markets. By the time large-scale production began in 1953, the Toyota BJ had already paved the path to overseas markets.
The leaf springs were supported by a full-floating front axle, 9 plates each with a 1,000mm span, a 45mm width, and 6mm thickness. The spring brackets were fixed by rivets.
The leaf springs were supported by a semi-floating rear axle, 10 plates each with a 1,150mm span, a 45mm width, and a 6mm thickness. There was lots of friction between the leaf springs while driving, which effectively reduce vibration to the body.
The ladder type frame on the Toyota BJ was built so that the distance between the side frames grew narrower as you approached the front. The front was narrower at the front in order to support the heavy front-mounted engine, while the rear was wider to provide stability for the wheels. There were 3 cross-members, with the side frame between the first and second cross-member being made of a high-strength box-enclosed type structure.