Repeat orders of Series 78

In the mid-1950s, all major private railway companies in Japan, except Tobu and Seibu (the latter continued to use second-hand parts they acquired from Japanese National Railways (JNR) to manufacture their own railcars), started using so-called "high-performance railcars". The most famous examples would be Series 300 of Teito Rapid Transit Authority, Series 2200 of Odakyu Railway and Series 5000 (first generation) of Tokyu Corporation, all put in service in 1954. Also in 1954, the Association of Private Railway Managers, the predecessor of the Association of Japanese Private Railways, created "common specification documents" of high-performance railcars on their concerns for the troubles that sales talks by the railcar manufacturers to railway companies would cause. In 1957, Series 3000 "Super Express (SE) cars" from Odakyu Electric Railways successfully underwent a series of test runs on JNR's Tokaido Line, reaching a then world record speed on the narrow gauge railways of 145km/h. It was also in 1957 when JNR reluctantly built a pre-production model of a new fleet, which was to be called Series 101, after all these developments which took place on private railway networks.

Tobu, on the other hand, did not build any new cars at all in 1955, probably studying these new developments taking place elsewhere. The evidence of their study would be the famous Series 1700 fleet for Limited Express services to Nikko, which was put in service in 1956. Although Series 1700 was not "long-lived", it was appraised as "the best of Tobu's railcars ever" until Series 6050 came in service in the late 1980s. However, for commuting trains Tobu stuck to their older design, and built Series 7850 (later re-numbered to 7890) with only minor modification to Series 7800. This decision, on which we can put many doubts with hindsight, would have been derived from the technical difficulties their engineers had to face after they introduced in 1953 the "right-angle Cardan drive" mechanisms in Series 5720, a predecessor to Series 1700 that were to be used for Limited Express services to Nikko. Series 5720 became the first service fleet in Japan to be equipped with such drive mechanisms; then, it would have been quite natural that engineers faced initial difficulties. These difficulties led them to the conclusion that the new techniques were not mature enough for commuting trains which require economy and reliability, a decision that was already only too conservative in 1956.

One thing to be extremely regretted, again with hindsight, was that Tobu did not re-design Series 7850 so that the fleet "looked" better, from both interior and exterior points of view.

The improvements of 7850 were limited to small modifications to the accomodation (especially introduction of toilets which were considered necessary for long distance services), and some technical changes. The technical bits were apparently more important, which includes change in the gear ratio from 1:2.87 to 1:4.13, together with improved weight distribution. The gear ratio change resulted in improved acceleration; while Series 7800 would be capable of only 1.6km/h/s (approx. 0.44 m/s2), the new Series 7850 could do 2.0km/h/s (0.56 m/s2). Later, some of the older Series 73 and Series 7800 cars replaced their gearboxes with the new one. I wonder if they encountered any troubles (especially shocks during acceleration) upon multiple working of newer and older cars with different gear ratios, which they did very frequently...

The production of Series 78 trainsets continued on, with slight modifications from time to time; Series 7820 came without toilets (first put in service in 1957), Series 7860 manufactured by Hitachi as "livery test cars" in 1958, and the final model was called Series 7870 (1960). (Note the cam-shaft controller change which took place in c. 1959; Later cars were built with ES-567-A from Toyodenki.) By the year 1961, when the last Series 78 trainset was built, the fleet of Series 78 became as large as 164 cars. However, as early as in 1960, Series 78 fleet would already have looked desperately old and obsolete from every point of view -- accomodation, technicalities like nose-suspension drives or laminated springs, exterior designs - virtually everything.