Which is stronger? When do I need a splined assembly? When do I need a tubular assembly?

We are not engineers. However, with tens of thousands of pto shaft repairs under our belt and who knows how many applications we have successfully modified or replaced, we can say this:

Engagement matters.

A splined shaft is only engaged (overlapped) by the length of the welded sleeve, which is usually 4-7 inches. So if you are spanning 60" from tractor to implement, a splined assembly is relying on those few inches to hold the entire assembly together and deliver the necessary torque.

A splined shaft is a tighter fit until it begins to wear.

A tubular shaft must be engaged by at least one half of its length at all times. Here some difficulty arises. The longer the tubes, the more engagement, the stronger the connection. Some say 2 thirds, some say 6 inches, we say half. But half of what?

At some point a tubular connection becomes stronger than a splined one. It will wear less over time and absorb thrust with more forgiveness. However, 10 inches of tube halves to 5 and this, in our opinion, is not acceptable.

Rule of thumb:

Shorter spans require splines. Longer spans operate more efficiently using tubes. if you must have a number, let's say 20. If your tubes are 20" long or more, then you should not need to consider splines as an alternative and retrofitting with a splined assembly will probably not solve any problem you may be having.

Conversely, if your tubes are 10-15" long, a splined assembly will improve performance and increase life expectancy.

Exceptions:

Exceptions to the rule would include low torque applications and some non-telescoping jack shafts. Short tubular assemblies are fine in these cases.

There are also medium length applications involving high torque requirements where a splined shaft holds up better. Everything is relative and everything is application dependent.

Other Considerations:

Other things come into play, primarily thrust. Do you require a clutch or other type of device? Do you need a constant velocity joint on either the tractor or implement side ? Do you use a three point, or hitch? All of these factors need to be taken into consideration as well as, "what is the purpose of the implement?" when trouble shooting PTO problems.

With the correct information, we have fit thousands of applications correctly. In many cases, we have improved upon the original equipment's design in order to increase life expectancy or improve performance.