Pinion / axle gears - How do they work?

Gota a 140 making noise from the xmission and need to fix soon. Started looking at the repair mannual drawings for xmission / differential / pinion gears, ext. I can't envision exactly how the pinion gears inside the differential casing drive the axle gears. I can see the pinion shaft is pinned in the differntial casing, but are the 2 pinion gears fixed on the pinion shaft, or do they turn freely?

If freely, looks like when in neutral if you turn one rear wheel one way, the opposite wheel will turn the opposite way.

If freely, how do the pinion gears drive the axle gears? Looks like the same teeth of the pinion gears would always be making contact with the axle gears. Is this the way it works? Never took one apart. Is the pinion shaft round or square where the pinion gears fit on it?

I understand how it works but not well enough to explain to someone else. The pinion gears are splined on output shafts but turn freely on pinion pin. If you jack both wheels off ground and turn them with engine through driveshaft they will turn in opposite directions (at least on car or truck never tried it on tractor). When going straight ahead assuming tires are same diameter and one is not slipping on ground the pinion gears do stay in fixed position and turn as if they were locked on pinion shaft.

See if I can take a reasonably coherent shot at it...

The pinion gears DO rotate on that shaft. As either side-gear turns, the pinion gears MUST move in opposite directions.

The shaft on which sit the pinion gears is fixed to the differential case and thus, of necessity, the shaft-and-pinions turn with the differential case and its drive gear.

When the tractor is driving flat and straight, neither the pinion gears, or the side gears (with the differential shafts), move in relation to each other, that is, the pinion gears do not, at that time, rotate on the shaft. Rather, they act as if they were all 4 welded together, and the pinion gears "drive" the side gears without any rotation on their shaft.

Of course, if the tractor were to only go straight, those gears COULD be welded together!

Even then, when a tractor turns and the back wheels go slightly different speeds, only then do the pinions rotate on their shaft, and only enough to allow the side gears (and differential shafts) to move at different rates from each other.

It"s counter-intuitive, because typically, one could expect "gears" to "spin", or be constantly rotating on their shafts.

Does that make any sense?

Yes, that makes perfect sense to me. Thanks for taking the time to explian.

If my understanding is correct, if I jack up the rear end and drive the wheels from the engine / transmission shaft, they will turn in the same direction, and the pinion and side gears will not turn in relation to each other (as you say - like they are welded together). If I then put the transmission in neutral, turning one wheel by hand will turn the opposite wheel in the opposite direction.

Nawlens, That's mostly it.

In neutral, when the differential drive gear is NOT turning, (and thus the shaft with the pinion gears is not revolving), then yes, the wheels will turn in the opposite direction.

When in gear, and the diff drive gear is turning and taking the pinion-shaft-and-gears with it, then the wheels will turn in the same direction.

However, in that last instance, when the wheels aren't 'bound' to the ground by their weight, and can 'free-wheel', I believe that though they are both going in the same direction, the potential exists for them to be slightly out of synch to each other (due to what? Maybe some variable resistance to one wheel due to difference in bearing tightness, or weight of tire, or one brake dragging, stuff like that), but yes, their tendency will be to rotate together in the same direction.

My memory told me wheels would turn in opposite direction when off ground and driven with engine. I had Chevrolet truck jacked up when I read your post so I checked it out and my memory was wrong (not the first time). On this truck left wheel turned a lot faster than right but brakes were recentltly adjusted and right one is probaly a little tight.