Greasable U-joints...

Not nearly as effective or foolproof as some people think. This one WAS greased, but the grease didn't flow to all 4 caps. The warranty on the reman driveshaft was long gone by the time the needle bearings powdered & fell out. And the owner/driver didn't pay attention to the vibration for over a year until it came apart on the road. Blind luck it didn't come up through the floor, or somersault the truck into a busload of amputee orpan nuns.

Sealed u-joints (which can still be greased by disassembly) are much stronger because they don't have grease journals drilled through the trunnion. And because they aren't constantly being blown out by grease being pumped in, their seals last MUCH longer, with less wear, and less contamination.

See also:
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Owner caption February 2016 · Photo 0 of 5000