Joe---There are several stages that U-joints can go thru on there way to
self destruction. They usually start with the needles in the bearing not
turning from lack of grease, age, or pick up contaminants. This causes
at least one leg of the cross to wear down and go out of round. This
then throws the transferring unit out of balance, allowing the propshaft
or axle shaft to vibrate at speed.
So. It is easy to see this in the latter stages of breakdown, as the
play between the bearings and their cross will be obvious. Early on, it
is difficult to determine a pending failure without being able to flex
the joint, by hand. Sometimes a shot or two of grease can temporarily
make the symptoms "go away". If this works, you were in the right place.
Dick
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