Greaseable vs non-greaseable joints, which is better?
In the past few years, this has been become quite a hot topic for debate. I'll get to the bottom line first, then explain the basis for my opinion.
Bottom line on strength: The non-greaseable joint is slightly stronger than a greaseable joint. The exact number, how much stronger, is unknown and we do not believe it to be very significant.
Bottom line on wear life: A regularly greased greaseable joint will outlive a non-greaseable joint. But a non-greaseable joint will outlive a greaseable joint that does not get greased properly.
Now I will elaborate. We have asked two of the major universal joint manufacturers who make non-greaseable joints for the numbers. Sure they are stronger, but how much stronger? We have asked them to give us the data, to tell us that a non-greaseable joint breaks at X foot pounds or that a non-greaseable joint is X% stronger than a conventional joint. So far, no one has been able to provide those numbers. I believe that it is kept a mystery because the truth is not as impressive as they want it to be. There is certainly something to the idea that having a solid joint makes for a stronger joint. Especially when talking about eliminating a hole for a grease zirk from the body of the joint. Side note, this is why we designed our Gold Seal 1310 series joints to have the grease fitting in the end of the cap instead of the body of the cross like a traditional joint shown below.
But there are also the holes that go through the joint from end to end, the ones that form the channels through which the grease flows. We don't believe these holes to have a great effect on the strength of the universal joint. The main reason for this is the location. They are in the center of the trunnions where the load is not concentrated. Universal joints are case hardened, the material at the center which gets removed when drilling for grease channels is soft and was never a source of much strength to begin with.
As far as wear life goes, and in our opinion the most important factor to consider when deciding which joint is right for you, the biggest question to ask yourself is "Am I actually going to grease my drive shaft?" If you are, get a greaseable joint. If you aren't, get a non-greaseable joint. Non greaseable joints are sealed better than greaseable joints. They are designed keep the grease in and the dirt and water out. However, there are two ways of thinking about it. One, you have a joint that you don't have to grease. Two, you have a joint that you can't grease. Even the best sealed joint will eventually dry up, the seals will crack, and moisture will find its way in. When that happens, the only thing you can do is to replace the joint. A greaseable joint on the other hand is something that you have to grease but you also get to grease. As long as you follow a regular maintenance schedule you will never have to worry about a rusty and dry joint. One last thing, and this is a big one, is that just because you don't have to grease your universal joints does not mean you don't have to grease your drive shaft. This is because there are other components that will almost always require a grease fitting. Two notable examples are the center ball in double cardan shafts and the slip yoke.
So there you have it. There is a big list of things to consider when choosing greaseable vs non-greaseable joints. At the end of the day, the right choice is the one you prefer. There is no right or wrong answer and it mostly comes down to personal preference.