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I will have to respectfully disagree with Rob. It's true that the Sherman changes the ground speed, but it also changes the PTO speed by the same ratio. So if you are running the engine at 3/4 throttle in Sherman direct drive for a 540 RPM PTO speed, then you shift to overdrive, you will need to run the engine at say 1/2 throttle to keep the 540 speed at the PTO, which in effect slows you back down on traveling speed. Plus this takes you out of the power band of the engine as the engine is made to run at so many RPM at 540 PTO RPM for maximum power. The Sherman is good for other tractor uses not involving the PTO. If you have the Sherman combination (over and underdrive) or underdrive, the underdrive is useful for a slower reverse or slower forward speed. The combination and overdrive is good for road speeds. Most of the time you will use direct drive. PS. If the shift lever is a dogleg (cast, curved shape), you have a Sherman combination. Forward is underdrive, middle is neutral, back is overdrive, and middle/out/back is direct drive. If the lever is a fairly straight rod with a threaded ball on the end, it is likely an overdrive, which does not pull out. Depress the clutch when shiffing it.
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