I have a twin-sticked Dana 20 from an Early bronco that keeps popping into Neutral. I've been running the tcase for a while and it has always done it. Last week i replaced all the helical gears (from a different failure) and it still pops out of gear.

What causes it? Bad shift rod pills/springs?

Usually the little teeth looking things on the gear that the shift collar slides over (and/or the floating shift collar) get worn. When new they are slightly angled in such a way as to pull the collar towars the gear that it is in (both under acceleration and deceleration). When they are worn it can be difficult to tell unless you really know waht you're looking for. Probably the used replacement parts are worn too much. HTH

A bungee strap is the most common fix for that.

Mine will pop out when I am in 2 low in 3rd or 4th and holding 3-4ooo rpms. I have been told it's the detent springs / the shift rails or both being worn. Now it's only in the snow and sand so it's not too big of a deal but it seems to becoming more of an issue so I will be pulling it apart soon to twin stick it, BMR repair the rails and shim the springs.

http://www.geocities.com/jeep_images/dana20/dana20_exploded.jpg

"I have been told it's the detent springs / the shift rails or both being worn."

This is the most common problem and I have been told you can order heavier detent springs durring rebuild so that it is less likely to happen after. I forget where you can get the heavier springs though...

I would say it needs a rebuild myself.

the heavy duty springs are in the mail, hopefully it works.