I was about 6 miles up a back country forest trail tonight, and had a weird thing happen. I was in 2wd at the time, and I was crossing through a deep ditch at an angle while driving on a steep uphill grade. The ditch turned out to be softer then I thought and the rear passenger wheel sank down pretty deep. This caused the truck to really flex the suspension in the rear, probably to its max, definitely the most I have ever flexed it. The rear passenger side tire was fully extended down, the rear driver side tire was tucked way up in the wheel well. I tried to gas it a little to get the rest of the way through the ditch. I spun the rear tires a little in the soft dirt, but then the engine just revved. As I gassed it, nothing was going to the drive shaft. I tried putting it into other gears (neutral and reverse), and nothing happened. I put it into what should have been neutral, and it made a grinding sound when I revved it. I finally got it into park. I crawled under and didn't see anything wrong. I was expecting to see my driveshaft laying on the ground or a broken u-joint or something. Everything looked fine.

Next, we got it into neutral, and pushed it back out of the ditch. Once I was on level ground again and the truck wasn't flexed anymore, everything started working fine again. I shifted through all the range of gears, and they all worked smooth just as they always have. I drove it back out of the forest road about 6 miles on pretty rough terrain, and then drove it home on the highway and city streets for about another 25 miles. Not a single issue at all that whole way. Drives just like it always had.

What could have caused it to lose the trans, but only while it was flexed really hard???

 

My guess is you probably pulled the drive shaft off the splines on your output shaft. Thankfully you didn't burr the splines enough so the the shaft slipped back in. Count your blessings!
If you determine thats the issue, its may be time for some longer bump stops and limit straps.

 

I'm guessing you might have extended the driveshaft to the point that the splines on the yoke were disengaged, but not enough to cause the shaft to separate completely.

 

Wow! Same reply at exactly the same time. Are we geniuses or what?

 

I thought that too when I crawled under to look at it, but the drive shaft didn't look like it was pulled out anymore then I have seen before. Guess it could have been though.

 

or fix it right, and put an SYE in it, along with a double cardan Tom Woods drive shaft, then the rear would be like the front, just bigger, and stronger, in the jeep world thats what we do for a lift over 3 inches, and thats why my cherokee is only lifted 3 as of now

 

So over on PS, they think that the flex caused the transfer case shifter to move enough to knock it between gears in the transfer case itself. That would definitely seem logical too and could explain the things I had happen.

 

how would flex cause that?
my jeep which has the same 231 case as our trucks have, has never done that, and ive flexed it to the point ive had tires in the air

 

Yeah, that makes no sense. The shifter goes right to the transfer case and is not connected directly to the body or the frame, so why would any flex cause that to happen?

 

My guess is the transfer case shifted part way into neutral.

The transfer case lever actually is mounted to the body (with a hinge type thingy), which is why when I did my body lift there was no reason to extend the shaft (it just adjusted with an adjustment screw/collar). My guess is the adjustment from the body lift is exactly "factory spec perfect" and when the heavy articulation occurred it shifted mostly into neutral.

If it was the splines on the drive shaft grinding from coming apart to far, I'm sure it would bur it up to much to actually slide back in again.