One of the best features about tractors is the versatility of the back end. The powerful diesel engine has an output shaft on the back coming out of the 3 point hitch known as the Power Take Off or PTO. This is an engineering foresight that will be difficult to match. With the invention and wide implementation of this single feature, it gave tractors the ability to use three point attachments that had gearboxes and other turning components without adding an external power source or alternate engine. While the diesel engine that powers the forward movement of the tractor spins, it turns this PTO shaft driving tillers, mowers, sweepers, and many other attachments that really crank out the horsepower and get the job done. When looking at PTO shafts, you have to understand the forces that are put on these essential components and the safety mechanisms that must be in place to protect yourself and your investment. The first thing you notice when looking at a PTO shaft is the plastic sleeve that encases the entire length of the shaft between the tractor and the attachment, the metal shaft is actually turning inside of this smooth protective casing, preventing curious onlookers from grabbing a high horsepower turning shaft and really doing some damage to their hands and arms. The next thing you might notice is the bolts and plates that are located at one end of the shaft, these bolts and plates are the automatic pressure relief system that manufacturers put on them to release pressure if for example a tiller digs partially into hard ground that it can not power through, one of two things will happen, the slip-clutch will engage and absorb most of the excess energy, or the "shear" bolt will break off allowing the PTO to turn freely while disengaging the power going to the actual working parts of the attachment. Tractor PTO shafts come in varying sizes, to get you close to the exact size of shaft that you will need for your specific purpose, but almost all PTO SHAFTS REQUIRE CUTTING FOR PROPER FIT! All of the different size machines available make it next to impossible to have a perfect fitting PTO shaft for every combination of attachment and tractor, so the manufacturers make these attachments very simple to cut, and Ted takes it a step further with a video here to show you the proper way to handle this easy task.
Important Things To Consider
When purchasing a PTO shaft, the size is one of the least important aspects due to replacement shafts almost always requiring cutting before installation, but the functionality and durability are two of the most important aspects to consider. If your need for a PTO shaft is to turn a fertilizer spreader/broadcaster, then you probably don't have to consider the pressure relief aspect, and a light weight shaft will probably be your best bet. However if you live in North Carolina like I do, and have to till up some of our famous hard, red clay, then you will need to consider the material your PTO shaft is made out of a little bit more than the next person. You will also have to make a decision between shear bolts, or slip clutches, depending on your preferences.