A series of minor modifications were carried out during the production life, but most of the design remained the same up until the factory closed in 1937. First to go was the four-speed gearbox, which proved unable to handle the engine's power. It was replaced by an unsynchronized three-speed gearbox, which was fitted to all subsequent Duesenbergs. Unlike almost all American manufacturers, Duesenberg did not switch to a fully synchronized gearbox in the mid-1930s, which made the Model J difficult to drive and outdated. By 1937 the chassis and gearbox were ancient compared to the competition.