International introduced the new TD-25 250 Series in 1959, which was really just a slightly modified TD24. At the same time, Caterpillar shocked the logging world with the introduction of the D-8 46A, a powershift tractor that left International trying to compete against it with the gear drive TD-25 250 Series. International Harvester engineers rushed to produce a powershift model, producing the TD-25 Bin 1962,
The old gear drive TD series was definitely a tough one to run compared to more "modern" dozers. I grew up on a 1949 TD9. It would do a ton of work. Later my brother bought a TD15B which was a much improved model, but that particular machine was a a pile of worn out junk. In the late 1980's I ran a local contractors JD750 then it was replaced with a new Case 1450. He died shortly after that. Now my brother has new Deere machines. They are a totally different machine. Growing up our neighbor was a operator from the late 1940's until he retired in the late 1980's. He had a lot of good stories. I always wondered how the Allis Chalmers HD16 with the self loading torque converter handled a down hill no-load situation. I asked him once and he simply said "not well"
