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Sidebar: Tractor PTOs

The Small Tractor FAQ
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Tractor PTOs

[Ronald Florence, Copyright 1987 Maple Lawn Farm, Inc.]

Traditional tools, like a moldboard plow or a disc harrow, do not require a power take off (PTO) from the tractor. Mowers, rotary cultivators, and a huge range of tools from seeders to cordwood saws to chipper/grinders do. For infrequently used tools, like a cordwood saw or a hay elevator, the PTO can be a real money saver; instead of buying and maintaining a whole shed full of small gasoline engines, you make use of a diesel or gasoline engine that might otherwise sit idle. Remember, though, that many chores are going to require using two tools at once. You can buy a chipper/shredder that mounts on the three point hitch and runs off the PTO, but if you want to use the loader on the tractor to bring material to the shredder, the operation may resemble a cross between a Rube Goldberg cartoon and Charlie Chaplin's travails in "Modern Times."

The most common PTO is a 540 rpm rear PTO, emerging in a six-spline, one and three-eights inch diameter shaft. The tractor tachometer is marked to indicated when the engine is running at "PTO speed." With rare exceptions, this will be the standard running speed of the tractor. Some older tractors have different style PTO shafts, which can usually be adapted to the standard shaft. Some smaller tractors, particularly the larger garden tractors, have PTOs with different speeds, such as 2000 rpm or 800 rpm, usually with a different shaft. In general, only a few implements are made to fit these non-standard PTOs; and they are sometimes costly. There is also little aftermarket for non-standard PTO implements.

There are a variety of means used to clutch the PTO shaft. The simplest is to use the engine clutch to engage and disengage the PTO. The disadvantage is that if the tractor bogs down or loses traction, or if a rotary cutter or a tiller jams, when you clutch to back up or engage four- wheel drive, the implement stops. It takes a while to get a rotary implement up to full speed, and you lose time and momentum.

The alternative is a "live" or independent PTO, which is clutched independently, sometimes with a two-step clutch pedal. Push down halfway on the clutch and you can shift gears on the tractor with the PTO still turning at full speed; push all the way down, and the PTO is disengaged. Because the implement keeps running at full speed, you don't have to wait before you move off again. Small tractors sometimes achieve "live" PTO's by using electric clutches, or by powering the PTO with a hydraulic motor.

The belly-mount mowers and front mount accessories like snow blowers usually operate off special PTOs, generally with electric clutches. These electrically-clutched PTOs are "live," but usually can only be used with one or two dedicated implements, rather than the wide range of implements available for the standard 540 rpm PTO.