Powered lift axle??

[Thorsteenster]

Originally Posted by SonoranWraith

Dig unit for crawling maybe?

That would probably be a little difficult to mount on the axle.
Here's a pretty straight forward driveshaft disconnect. Use male Stampede drive shafts on the rearmost pass through axle and on the lift axle, then a female to go over the two to slide back and forth, joining the two males end engaging/disengaging drive. I did this with Revo shafts a few years back, into one of the male ends I threaded a bolt with the head rounded off to keep the female slider in place while disengaged and I used an old steering knuckle around the slider attached to a servo to move it. You'll have to figure out how to keep the knuckle in place laterally on the slider while allowing it to spin.