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On my 81, three of the four half shaft U joints have grease fittings. One does not, and has a pronounced dished in center, as compared to the other three.
Upon quick inspection, it looks like the drive shaft U joints are non greasable.
The manual refers to non greasable units....so should I assume the three with grease fittings were replaced at some time???
Why would someone do just one of the two on a half shaft? Makes no sense to me? If one failed, I would think the other may be on the way out too. Might as well do them both.
Should I plan on replacing the non greasable units soon, before failure.?
Greasable u-Joints have a hollow core allowing grease to tranfer to end caps. Heavy duty Joints do not have a hollow core and are non greaseable.
Make your own decisions on this based upon your driving style
My 77 was the opposite - three non-greasable u-joints and one with a zerk. The other four had bosses cast for the zerks, but no tapped holes.
They are made from the same outer molds(in this manufacturers case), greaseables get drilled thru or an internal mold added for grease transfer. Non-greaseables were used, and should be used, because of their added strength. They may not last as long, but they are less likely to break, VERY important for half shafts. They take alot more stress than driveshafts (load bearing suspension member, and tourqe multiplication by rear end gear), and also because catostrauphic u-joint faileur brings on a whole new meaning in their case.