Rear end gone???

[Adam m]

Okay so I was under my truck doing the front differential bushings and u gotta take off the front drive shaft so I did well it got wedged so I thought, so as soon as I prayed it off my truck starts rolling backwards and right on top of my leg/foot which that's neither here nor there but my question is... Wth?! That should not have done that, and when my wife jumped in it after screaming for 10 minutes for help, she put it in drive and it wouldn't move acted like it was in neutral.. so can someone give me a place to start?? Rear diff, transfer case,? I get 0 codes about anything even closely related and if I have no rear wheel drive it's been like this for monthsssss any help will be greatly appreciated
Oh yeah it's a 07 Yukon Denali xl

 

[mikez71]

AWD differential? Similar to lifting both rear wheels off the ground in park, but you can spin the wheels.

 

[Charlie207]

Did you set the parking brake, chalk the wheels?

 

[strutaeng]

What?! Truck rolled backwards after you removed the front driveshaft and pinned your leg? Are you okay?

Safety first man. Parking brake. Chock the wheels on both sides (front and back) if you are removing the driveshaft, especially if on a slope.

But removing the front driveshaft by itself should not allow to the vehicle to roll backwards unless you had already removed the rear driveshaft and hadn't engaged the parking brake, and you were on a slope. The parking pawl on the transmission is the one that keeps the vehicle from rolling when you throw it Park. That's why the vehicle always seems to roll just a bit after releasing the brake pedal; it's the pawl engaging on the teeth.