I just want to make sure we're replacing the right stuff. Neither of us has has a 4x4 before so we're trying to diagnose and fix problems we've never faced before. We have a '96 Blazer (S10).

For a month or two there has been a slight grinding sound that we couldn't figure out, only that it was underneath the truck. Came home from work one night and right before I got home it went from a slight grind to a loud clank-clank.

We attempted to drive to the store just down the street but the clanking didn't ease up, then less than a mile down the road, the (rear?) wheels locked briefly (I was going about 30). When I accelerated, the clanking eased, but taking my foot off the gas made it clank pretty loudly and lock up sporadically.

We got it home and parked, bought a used transfer case and was told the U-joint in the rear may need to be replaced.
If anybody is familiar with this issue, I'd appreciate feedback before we start to take the driveline off. Saw some great video of how to remove and replace driveline and u-joints but still, first time, little nervous.

Thanks!

 

What happens when you try to engage 4wd? Does it engage? Does it have any impact on the noise?

Replacing the u-joints isn't bad, but you'll need a press (hydraulic works best, but a bench mounted vice press will work) and some sockets (one that is just a bit smaller than the OD of the u-joint cups and one that will allow the u-joint cup to go inside it). You will also need a torch if the u-joints have never been replaced as the factory cups are held into the driveshaft and front yoke by injected nylon plastic that needs to be melted out while applying pressure to remove the cup.