In a heavy-duty twin countershaft transmission, which gear floats between the countershaft gears when disengaged?

• A. input shaft
• B. countershaft
• C. mainshaft
• D. output shaft

Answer: (C)

In a heavy-duty twin countershaft transmission, power moves from the input shaft to the countershafts and then to the mainshaft through a set of gears. Each gear ratio is created when a gear on the mainshaft meshes with a specific gear on one of the countershafts via a synchronizer or dog clutch. When a gear is disengaged, the gear on the mainshaft that would connect to the countershaft gear is no longer meshed with either side. It thus sits between the two countershaft gears, effectively floating until a new engagement is made. The countershaft gears themselves stay fixed to their shafts and aren’t the ones that float. So, the gear that floats between the countershaft gears when disengaged is the gear on the mainshaft.