AMC 20 rear questions

I currently own a 1985 CJ-7 4cyl. with amc 20 (3.54 gears) and it is my first jeep. I am going to replace the two piece axles for one piece axles but I keep keep hearing but wide trac and narrow trac. Can someone explain the difference or what what I can look for to tell the difference. The reason am replacing the axles is I went to pull out onto the highway and the rear of the jeep started to shake like something was vibrating (extremely). It didn't feel like a clutch does when it slips. The less accelerator I gave the less it vibrated. I am I correct in my diagnosis? Any info or suggestions are welcome. Thanks in advance.

That vibration could be any number of things, driveshaft, loose pinion or a two-piece shaft that is ready to snap. Wide track and narrow track just refer to the width of the axle, since you have an 85, it is a wide track. Definatly worth upgrading no matter what. I snapped mine and the wheel fell off, luckily I was not going that fast.

While your doing the upgrade they make kits that have the axles, and a locker together so you can do it all at once and save some money.

I wouldn't suggest a locker though with the 2 piece axles. I had that setup, and broke an axle. I didn't know it however and eventually broke the locker too.

As for the viberating I'd check your U-joints too, that is one possibility.