Your wheel spinning test will not give you any indication if the transmission is in neutral. Doing that with the transmission in gear (engine off) is the true test of either a totally destroyed u-joint or a problem in the differential or broken axle.

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.