Purchased my 2004 GMC 2500HD Duramax/Allison back in March & ended up in snow with it for the first time yesterday.

I had to park on the side of the street & as soon as the right-rear wheel got in the snow it just spun - left wheel was on pavement. It was in 4-wheel drive, and the truck was just sitting there idling & the right-rear wheel was slowly rotating in the snow.

I thought the full-locking differential wouldn't allow this to happen.

What's up?

The rear end has a governor locking diff and the wheel spin has to have a 100 rpm differential before the diff locks up. Then, if the wheel speed is greater than 20 mph the gov lock disengages.

If you goose it a little, it will lock up. But hang on, she'll go sideways on you if you're not prepared.

The rear end has a governor locking diff and the wheel spin has to have a 100 rpm differential before the diff locks up. Then, if the wheel speed is greater than 20 mph the gov lock disengages.

If you goose it a little, it will lock up. But hang on, she'll go sideways on you if you're not prepared.

Cool - that would explain it (I think I was experiencing some of the sideways stuff you mentioned...)

I assume this is true in reverse also - diff locks up over 100 rpm of the wheel?

Yep that's correct. That's how I put a dent in the side of the bed when the truck was less than 1 week old. Fortunately, it didn't damage the paint and the dent was popped out and a little polishing by the body shop did the rest.

My driveway was snowy covered and it is at a slight incline. You can imagine what happened when I goosed the throttle.