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While I had the rear end of my '74 Ford F100 off the ground replacing the rear brake shoes, I noticed that both rear axles turned freely with the tranny in park. The drive shaft did not turn cause the tranny was in park but why did the axles turn? Does my truck have a faulty rear end?
It is alright. You simply have an open carrier and one wheel turned one direction while the other one turned the opposite direction. Normal for an open differential.
If you place one tire on the ground and try it again, you may would not be able to turn the wheel.
If it was broken then the truck would not move without making a bunch of noise.
Thats all normal. If one tire is on pure ice on a hill and the other is on dry pavement one tire will rotate forward and the other will go backwards. Thats one of the reasons why they invented the parking brake and you should use it.
psquare is right. That's the purpose of the spiders, so that the axles can move at a different rate than the ring gear. And spider gears should never be touching the ring gear. If that's the case you might have a problem.