Originally Posted by Macrobb

Replace it.

U-joints are one of those 'replace or grease regularly' parts, and people tend to neglect them.
They aren't too expensive or hard to replace - even if you don't have a proper press or vice, you can make do with a big hammer and sockets for spacers.

I recently went through two of my trucks drivelines - I pull the rear 4 bolts on the differential(On all my trucks, they are socket head cap screws, so I use a 3/8 adapter)

I then remove the two bolts holding the carrier bearing, drop that and slide the whole assembly out.

The two-piece driveshaft can then come apart - you'll need to cut the retainer ring on the rubber boot on one side at least.

Once it's apart, you can then go after the bearing. This is... a challenge. I've ended up cutting them apart on the last two I did. Just cutting the outer race with a grinder until it falls off, then cutting the inner race enough and breaking it with a chisel.

New one shouldn't be nearly as big of a problem to put on, but you'll definitely want to clean up the entire seating surface with a wire brush to get off any rust or crud. I use the old pieces of the inner race for a surface to beat on with a hammer and slowly work the new bearing into place.

At the same time, I'll replace any iffy U-joints, and grease the others. Then, reinstall.

The only tricky bit I've found is that Autozone can't figure out the correct carrier bearing for my trucks. O'reillies had the right one in their computer and in stock.