...when they designed the drivetrain for the Greyhound Scenicruiser bus back in the early 1950s? The supersized new bus was too heavy for the 6-cylinder diesel engine they used in their standard-sized buses, and their V-12 engine, twice as big, was far more than was needed. They did not wish to outsource for a Cummins or other competitor's engine, and for some reason did not wish to expedite development of a V-8. Thus they used a pair of their 4-cylinder engines, each with a fluid drive and the output shafts geared to a common shaft. So far so good, at least on paper. It was the Rube Goldberg contraption from there to the wheels that has me scratching my head. The shaft from the fluid drives went to a 2-speed electrically shifted planetary gear set, followed by an electrically operated clutch and a conventional 3-speed manual-shift transmission, resulting in 6 forward speeds. The planetary was operated by a switch on the gearshift stick. If I am not mistaken the shifting sequence was as follows: Start in 1st with the planetary in low; upshift the planetary; simultaneously downshift the planetary and shift the 3-speed to 2nd; upshift the planetary again; simulaneously downshift the planetary and shift the 3-speed to 3rd; upshift the planetary a final time. This required retraining of drivers who had been driving conventional 4-speed transmissions in previous buses for years. If that wasn't enough, the electrically operated clutch was all or nothing, with nothing to soften the engagement. This made smooth shifting difficult. The designers must have thought the fluid drive would take care of it, but apparently not. Within a year they were replacing it with conventional mechanical linkage to the clutch, enabling the drivers to engage the clutch gently. Even after the change many drivers did not like the system and it was a maintenance and breakdown headache. By 1961 GMC had a V-8 diesel in production, and all of the Scenicruisers were rebuilt with the new engines and conventional 4-speed transmissions. I never rode in a Scenicruiser, but I rode in equally large MCI and Eagle buses with the same powertrain, and the performance seemed entirely satisfactory.

What really amused me was a 1957 Popular Science Monthly article in which the original system was cited as a virtue by the author. The thinking was that if one engine failed, it could be disengaged by dumping the fluid in its coupling and the bus could be driven at reduced speed to the next city or town on the other engine. In actual fact drivetrain breakdowns were far more frequent than engine failures. Those old Detroit Diesel engines were practically bulletproof.