How Does a Transmission PTO Work?

by Derek Odom

The Drive Shaft

A power take-off (PTO) assembly is comprised of an extra driveshaft coming out of the gearing of the transmission, usually found on farming equipment. Sometimes, commercial vehicles and off-road trucks can come equipped with them to power winches or snow plows. The drive shaft works like the ones that power the wheels, but instead use their rotating motion to power an accessory. A power take-off drive shaft is also connected at both ends using universal joints, like the ones found under vehicles.

Accessories

Some of the things a power take-off assembly can power are winches, operating the tilting bed on a dump truck, the garbage compactor on a refuse vehicle, or they can even run the huge water pumps found on fire engines. They also power many of the farm implements seen towed behind tractors. Normally, an air valve is used to engage or disengage the power take-off assembly, but mechanical and electrical options are also available, depending on the application and year of manufacture.

Safety

While a power take-off device is extremely useful and helps to get many jobs done, they are very dangerous, especially if proper protection is not in place. Many power take-off assemblies come with shields that help prevent articles of clothing or appendages from getting wrapped up in them, but many do not. Even for the units that do, the spinning driveshaft can be deadly. Extreme caution should be used by anyone who is anywhere near one. Many have incurred horrible injuries. Some have even died because they became entangled in a power take-off assembly. If installing a PTO assembly on your own vehicle, take every measure possible to ensure the correct unit is installed, and that no binding or interference will occur. It is not recommended for someone who is not mechanically inclined or trained properly to install or operate a power take-off accessory. The PTO will be power rated, usually in foot-pounds of torque. Make sure the power take-off that is used is powerful enough to effectively operate the accessory. Keep the universal joints greased and in good working order to prevent failure, and possible damage to the drive shaft or the accessory it powers.

About the Author

Derek Odom has freelanced since 2008 and is also an author of the macabre. He has been published on Ches.com, Planetchess.com and various other websites. Odom has an Associate of Arts in administration of justice.