The chassis of the Toyota Jeep BJ was based on the SB-type 1-ton truck (with an S-type 995cc engine) that was originally released in 1947. For that reason, at 2,400mm the wheelbase about 200mm longer than that of the Jeep, and the body was also a size larger.
The SB-type compact truck was commonly known as the Pony Toyota (and later the Toyopet Truck), and because it was designed as a small transport vehicle that could also double as a passenger car, its suspension settings were likewise soft. These characteristics were carried over into the Toyota BJ-type, so it gave a surprisingly comfortable ride.
The engine was a 3,386cc water-cooled in-line 6-cylinder B-type gasoline engine. Jeeps being built at that time had a side valve construction, but the B-type engine was an OHV type. The engine was originally designed in 1937, with the first prototype completed the next year in 1938, after which it was installed in the GB-type truck, the KB-type truck, and the BM-type truck, being primarily an engine for 4-ton class trucks.
The capacity of the B-type engine when it was first developed was a maximum output of 75HP/3,200rpm, and a maximum torque of 21kgm/1,600rpm. Later these specs were improved by boosting the compression ratio and through other refinements, so that whereas the first model Toyota Jeep BJ model had a maximum output of 82HP/3,000rpm and a maximum torque of 21.6kgm/1,600rpm, by the late model version the power had been boosted to a maximum output of 85HP/3,200rpm and maximum torque of 22kgm/1,600rpm.
This meant reserve power for the size of the body it was mounted in, so the Toyota Jeep BJ came without a LO ranage subgear.
The Toyota Jeep BJ was completed in 1951, and first unveiled that same year at a public showing of Toyota vehicles. There were 26 Toyota vehicles displayed at this event, and during the 3-day period the attendance amounted to some 200,000 people. Moreover, the design of the Crown was begun in 1952, with the first Crown model built in 1955.
At the time it was considered unusual to say the least to match a 4-ton truck engine with a compact truck chassis, but in reality these were the only materials that Toyota had to work with. It turned out to be a successful combination. An ample sized body useful for transporting materials driven by an engine with power to spare, this model met multiple needs in the market for a compact 4x4 vehicle at a high level.
Moreover, the fact that it was not adopted for use by the Police Defense Forces actually turned out to be a major stimulus for the development of an export strategy, with considerably more freedom in design and development, and became a key factor in Toyota's successful overseas launch.
However, in 1953 Toyota did receive a procurement order from the National Police Agency, and the plant in charge of production was the Arakawa Bankin Kogyo KK (now called ARACO Corporation). With regular orders for large-scale production, the factory literally worked around the clock to meet demand.
The process worked like this: first the parts for the chassis would be shipped from Toyota Motor Corporation for assembly at the Toyoda Automatic Loom Works, Ltd., then transported to the Arakawa Bankin Kogyo KK, where the body was painted. The completed vehicles would then be shipped overland back to the Toyoda Automatic Loom Works, Ltd., where they would be inspected by officials from the National Police Agency, whose demands could be met by a team of about 20 people who could do finishing work and make adjustments.
The Toyota BJ-type was a multi-purpose compact truck based SB-type truck, and went through a series of body shape design changes over time. The original short body hooded cargo and passenger carrier type was converted to a metal top type, and a closed type passenger model was also released. For the cargo carrying version the rear was extended by 500mm and converted to a pickup truck, and there was also a truck with a separate unit cabin and truck bed.
There were many variations according toBecause the body has a rather squeezed nose design, the diameter of the steering wheel covers about half of the instrument panel. For that reason the driver's seat feels rather cramped, and when you carry a passenger it makes it a bit difficult to steer. In the later 20-series models the steering wheel was moved further to the outside. where the spare tire was located, not only on the rear gate, but even on the front fender or below the truck bed.
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 triggerd 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.
References : toyota.com