allowing the bus to rapidly return to revenue service while leaving the powertrain in the shop for repairs. The original buses had a 4-speed non-synchronized Spicer manual transmission with a solenoid reverse. The manual transmission 4107 and 4903 models were notorious for being difficult to shift through the gears, often making loud, grinding noises that tended to upset the passengers. The technique known as "double-clutching" reduced these embarrassing noises, but even the most skilled driver would occasionally have problems, especially when changing buses (and/or powertrains) gave them an unfamiliar feel to clutch and shifter. Second generation: GM PD-4108 and PD-4905 In 1970, design improvements came with the updated versions, PD-4108 (35 ft) and PD-4905 (40 ft) both with a 24-volt electrical system. The driver's controls were updated for both. The biggest complaint about the 4905 and 4903, from the drivers' point of view, was that the extra of length was all between the front and rear axles. It was very easy to scrape the baggage compartment doors on tight turns. The 4905s looked just like 4108s but with three baggage compartments. In addition, synchronized gearboxes were added in the second generation. Some 4905s were equipped with a tag axle at the factory, with a single extra wheel on each side, located in the third baggage compartment for states with lower axle load limits. The tag axle was forward of the drive axle, so turning radius was not affected. In 1972, the PD-4108 was redesignated P8M4108A, and the PD-4905 became P8M4905A. In 1979 and 1980, the P8M4905A was replaced with the short-lived model H8H649, which added an automatic transmission from Allison for the first time. Markets The GM Buffalo models were purchased primarily by affiliates of the National Trailways Bus System and many other smaller operators. After the Scenicruiser exclusivity arrangement with GM, Greyhound purchased an interest in Canadian bus manufacturer Motor Coach Industries (MCI), and by the mid-1960s, it had switched most of its purchasing over to MCI products. In the 1970s, MCI products began to overtake the GM Buffalo models in sales volume, especially after the introduction of the popular MC-8 at the Transpo 72 exhibition held at Dulles Airport near Washington, DC, in 1972. As the market share declined, GM lost interest in updating its intercity motorcoach products. When the GM RTS bus models replaced the fishbowl models in GM's transit bus offerings in 1977, the loss of