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.

 

[Doubeleive]

for future reference
AWD- does not have park (not really) what it does is it binds the front and rear wheels together
lift either end up and the other end will roll away.......
don't believe me? ask the guy above with the crushed foot or go ahead and try it yourself, if you do I would highly suggest you be prepared for the consequence.

 

[Doubeleive]

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

normal, AWD will roll away if either end is lifted up, has no real "park" instead it binds the front/rear together
unfortunate way to find out....
ALWAYS chock the wheels and set the parking brake, even then I don't trust 3 tons with my life very much

 

[Adam m]

It wasn't lifted at all I just crawled under it. N all 4 wheels were on the ground now chalking I should've known better but I wasnt expecting that. Yes awd differential. The parking brake wasn't on but it was in Park. That's why im scratching my head like wtf yeah I'm alright could've been A LOT worse no broken bones just a lot of bruising

 

[Doubeleive]

It wasn't lifted at all I just crawled under it. N all 4 wheels were on the ground now chalking I should've known better but I wasnt expecting that. Yes awd differential. The parking brake wasn't on but it was in Park. That's why im scratching my head like wtf yeah I'm alright could've been A LOT worse no broken bones just a lot of bruising

unbolting the driveshaft is no different than lifting the truck up, same difference, same result

 

[j91z28d1]

ouch..


but yes, this is just how the all time awd transfer case works. you have a parking paw in the transmission, not the transfer case. so paw lock the output shaft of the transmission in park. but the transfer case isn't locked. once you took the drive shaft off the front, it is basically in neutral.

best way described it is think of your rear diff of a 2wd. put the truck in park, jack up both back tires and they will turn freely but on the opposite direction. same with the transfer case. you didn't notice but once you popped the drive shaft off, it was spinning the opposite way of the one going to the rear end as it rolled over you.


the other kind of case with 2wd, 4h/4lo 4x4 transfer case it different. when it's in 2wd it shouldn't roll away.

 

[donjetman]

@Adam m
Totally normal for the BW4485 awd transfer case
It been discusssed here before.

 

[Adam m]

ouch..


but yes, this is just how the all time awd transfer case works. you have a parking paw in the transmission, not the transfer case. so paw lock the output shaft of the transmission in park. but the transfer case isn't locked. once you took the drive shaft off the front, it is basically in neutral.

best way described it is think of your rear diff of a 2wd. put the truck in park, jack up both back tires and they will turn freely but on the opposite direction. same with the transfer case. you didn't notice but once you popped the drive shaft off, it was spinning the opposite way of the one going to the rear end as it rolled over you.


the other kind of case with 2wd, 4h/4lo 4x4 transfer case it different. when it's in 2wd it shouldn't roll away.

Really? I never knew that. Damn that's a ****** design. So the. The only that would be possibly broken is the pawlock

 

[Adam m]

So okay 1 more question so after I screamed for my wife to come outside n help me, I told her jump in put it in drive n go, u kno thinking that it should still have rear wheel drive,no? Well it didn't go anywhere it just acted like it was in my neutral which actually made those situation worse because then it had to rock back a little bit more to catch that lock or whatever so is that correct then like if you take your front drive shaft out on all wheel drive vehicle you don't have rear wheel drive still??

 

[Doubeleive]

So okay 1 more question so after I screamed for my wife to come outside n help me, I told her jump in put it in drive n go, u kno thinking that it should still have rear wheel drive,no? Well it didn't go anywhere it just acted like it was in my neutral which actually made those situation worse because then it had to rock back a little bit more to catch that lock or whatever so is that correct then like if you take your front drive shaft out on all wheel drive vehicle you don't have rear wheel drive still??

not sure on that one, the front is a open differential even with awd, so it might have detected wheel spin and maybe tried to decide what to do, kind of like if you have ever driven up on a curb while moving and it detects a different wheel speed the 1st thing it does is basically stop for a second then it goes again. just guessing though. you would know if there was a drivetrain problem as it would throw abs codes or traction control errors, etc
I believe there are some cases where if one wheel is spinning freely it can basically disable you, but I could be wrong

 

[j91z28d1]

Really? I never knew that. Damn that's a ****** design. So the. The only that would be possibly broken is the pawlock

nah, nothing is broken. or it would have rolled away before you removed the front driveshaft.


your truck is working as designed. nothing is broken.

always set your parking brake on vehicles.

 

[j91z28d1]

not sure on that one, the front is a open differential even with awd, so it might have detected wheel spin and maybe tried to decide what to do, kind of like if you have ever driven up on a curb while moving and it detects a different wheel speed the 1st thing it does is basically stop for a second then it goes again. just guessing though. you would know if there was a drivetrain problem as it would throw abs codes or traction control errors, etc
I believe there are some cases where if one wheel is spinning freely it can basically disable you, but I could be wrong

usually what happens in other gm newer gm cars is they will apply the brakes to the one spinning wheel to keep you from just sitting there spinning one tire. of course this only works when it's on and running. not off in park.


it's kinda a fake torque vectoring. the real stuff is when the diffs are electronically controlled to send tq around the system. this just uses abs systems to keep one tire from freely spinning and you not going anywhere. I'm sure it works pretty well though for what's beefed.

 

[mikez71]

So you did pop the driveshaft out of the transfercase before/as it started rolling?

Because it could have been bad if still attached to the transfer case when you told her to hit the gas...

Reminding me of a video where a guy's jacket sleeve caught and sucked him into a big lathe.

 

[mikez71]

So okay 1 more question so after I screamed for my wife to come outside n help me, I told her jump in put it in drive n go, u kno thinking that it should still have rear wheel drive,no? Well it didn't go anywhere it just acted like it was in my neutral which actually made those situation worse because then it had to rock back a little bit more to catch that lock or whatever so is that correct then like if you take your front drive shaft out on all wheel drive vehicle you don't have rear wheel drive still??

Exactly. It is just another differential between your front and rear driveshafts.
In the 4WD tahoes, there is no diff in the xfer case, it just locks front and rear together. Rear is always connected.
An AWD sytem with all open diffs could potentially(theoretically?) get 3 wheels stuck and spin one wheel. (without traction control)

 

[donjetman]

what @j91z28d1 said above.

 

[Charlie207]

So, to recap, just so we're all on the same page: OP did not set the parking brake, or caulk any wheels before disconnecting the driveshafts?

 

[Adam m]

So you did pop the driveshaft out of the transfercase before/as it started rolling?

Because it could have been bad if still attached to the transfer case when you told her to hit the gas...

Reminding me of a video where a guy's jacket sleeve caught and sucked him into a big lathe.

That's exactly whG happened it wS still attached to the transfer case. At the time I didn't care it was on top of me and I just wanted it off. When I pulled the driveshaft out everything looked fine nothing ate up