Announced in May 1956 as a new truck for medium distance services, the Model RK52 was the predecessor of the Dyna. The roots of the RK52 go back to the KA1-KA4 semi cab-over-engine trucks, which were independently produced in small numbers at Toyota Auto Body based on the chassis of the Toyopet Model RK1.5 truck and had been around for about a year. In April 1956, as the Toyopet truck was upgraded to the RK23, the new chassis and an enhanced body of the KA were fitted together as the Toyopet Model RK52 route truck.

Although the RK52 had the same length as the RK23, its cargo bed was 625 mm longer and therefore larger. The passenger capacity (two) and the maximum payload capacity (1.5 tons) were the same as those of the RK23, and so was the 1.5-liter 48 hp engine (Type R). In addition to the truck, a route van featuring double doors in the rear was also available. The route van had a more vertical windshield than the truck's, and its headlamps were positioned higher, while the doors were moved a little toward the rear to facilitate the entry into/exit from the rear cabin. In October 1956, the model was succeeded by the RK62 which featured an enhanced Type R engine (with the output boosted from 48 hp to 55 hp) and an increased payload capacity of 1.75 tons.