I recently received some old ball joints from Hellbound13. Thanks Hellbound!
I cleaned them up and dissected them to see how they are made, how they function, and determine if they can be made grease-able.
This is what I came up with:
The lower ball joint is designed to bend, rotate, and have no axial or radial movement. They come from the factory with no grease fitting. An inspection of the internal parts revealed it is designed to be grease-able. The amount of grease found in the ball joint was no more than what would be called "butter lubricated" during assembly.
The plastic socket liner has a hole in the top, and grease grooves going down the inside where the ball resides.. The very top of the ball is flat, making a nice grease reservoir. The top of the ball joint body can be drilled in the center without risk of damage, and tapped, providing suction is used to keep the filings from entering the joint during each operation.
There isn't room for a regular zerk fitting because the u-joint yokes will hit. At least that's the case on my Rubicon axle. A flush fitting would work. Here is one source: h**p://www.saeproducts.com/flush-grease-fitting-AK18F.html
Installing a grease fitting in this joint, on the vehicle, would be difficult. I would recommend doing it on the new joint, before installation.
The upper joint does not bend. It can rotate and is designed to allow for axial movement, and no radial movement.
The amount of grease found in the ball joint was no more than what would be called "butter lubricated" during assembly.
Installing a grease fitting in the upper joint is not recommended, as the pressure would likely blow out the thin plastic cover on the top.
The plastic liner in the joint is designed to make up for radial wear, for a while, at least.
So, installing grease fittings in only the lower ball joints may sill extend the lives of all four ball joints.