hmm. with the wheels on both axles, if you spin one in neutral the axle will try to spin the tranny. if you put it in 1st, it will spin the tire on the opposite side of the dif. try it both ways. of course, you will need to lift both rear wheels off the ground to do this... anyway, check to see if it's any different in/out of gear and from one side to the other. this will narrow your search. I would think with the tires on, and trans in gear, the rear tires should freewheel when you spin it pretty good.
John

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!