Rear end question

[Uncle Dan]

My Monte has been sitting up on blocks and jackstands with the suspension hanging down at its full lower limit of travel (wheels and tires off) for about the last three weeks. From time to time, whenever I had a few spare minutes, I'd been taking care of some brake/shock/etc... work.

At some point in all this, I started to be able to turn the rear wheel hubs without any corresponding movement in the driveshaft at all. The differential seemed to be working, in that the opposite side wheel would turn in the opposite direction as expected. But the driveshaft didn't spin a fraction of a turn & come up against resistance from the trans being in park, like normal.

Needless to say, I got a little worried that I'd fubar'd something, and rear end repair is beyond my level of competence. My brother and I put our heads together & decided not to sweat it unless there was still a problem once the car was back on the ground.

Well, now she's on the ground, and it's as if nothing happened. Drives around just fine. Now, granted, it's still not "on the road," just riding around the farm. So I don't know how it's going to behave above 20mph yet.

But do I have a problem? Should I expect one? What could have lost contact between the pinion flange, pinion gear and ring gear, and is it likely to happen again unless I straighten it out? Or is this normal & I'm just worried about nothing?

 

[307 Regal]

I think that's perfectly normal. The axles can rotate without spinning the differential. That's why one wheel can spin the opposite direction. They're just interacting with the spider gears.
Your pinion gear spins the ring gear & the differential that it's bolted to. It's the spider gears that translate that action to your axles, due to the way that they're mounted to the differential housing. Take a look at these:

 

[307 Regal]

But the driveshaft didn't spin a fraction of a turn & come up against resistance from the trans being in park, like normal.

It works like that because on the ground, in order for the car to roll, both wheels have to spin the same direction. And they can't spin in the same direction without rotating the whole differential thanks to the spider gears.

 

[Uncle Dan]

Thank you very much for taking the time to post that. Watching the cut-away diff working really helped.

What really had me wondering was that when I first lifted it up, any jiggling of one wheel or brake drum would make the driveshaft try to spin, stopped by the trans being in park.. This is what I'm used to; it's all I ever remember happening in this situation, though it's been years since I've screwed around under a car. But after a week or so of hanging there, it changed to freewheeling. It was the change that got me.

So, if I now understand correcly, when I grab a wheel and try spin it, it's normal for it to do one of two things:

Either the axle that I'm spinning rotates the cage by friction/lack of lube/whatever, in which case the ring gear will rotate & spin the pinion, producing the effect I'm accustomed to.

Or, if the axle spins freely within the cage, it will just rotate the other axle freely in the opposite direction via the spider gears.