ok, was driving to school and noticed a very harsh clicking noise, and a heavy vibration in my floorboard. got out to check what was going on and the cap for my u-joint had fallen off, making a fair amount to play in my front passenger axle.

after i replaced the u-joint, i went to test drive and when i engaged into 4x4 a loud pop and then a bunch of little clicking noises (prior to dropping it into 4x4 i ran to the local walmart, it ran just fine). perhaps i broke a spider gear or something? thoughts?

 

I assume you checked the ujoint, check the other one,check the hub bearings and front driveshaft too. There is also a small bushing in the end of the passenger side shaft where it mates to the inner shaft. I would take off the CAD and make sure it's there, plus you can make sure the shift fork and collar are on right. You"ll also want to check the vacuum at the 2 hoses going to the shift motor on the CAD. One hose will have 15lbs in 2wd(0 in 4wd) and the other will have 15lbs in 4wd(0 in 2wd). Maybe it's not engaging/disengaging all the way.