Has anyone had to replace worn/bad u-joints on their 1st gen Xterra? I called a couple of local parts store with no luck. Then I called the dealer and they said that they do not offer just the u-joint but they sell the whole rear drive shaft with the u-joint's permanently installed. Anyone hear of this?

you can replace just the u joint (I personally havent had to replace mine yet) I know 4x4parts.com does sell a pair of u joints for like 30 bucks... if i am not mistaken you can ask for the part for a frontier and it will fit (someone plus confirm this). When I do the ball joints I have ask for frontiers ones since they "say" you can't buy ball joints seperate of the control arm for xterras...

No parts stores will have a listing for the u-joints. They are a 1310 joint. Any parts store will stock them. Don't buy the ones from 4x4 parts, they are a bunch of crooks with their ridiculously inflated prices on them. Last time I checked they were $30 EACH from AC which Is robbery.

^^^ Any parts store has these. Kind of a pain but not a hard job;

What I do;
If I remember I spray some PB in there a couple of days before.
Mark the DS and the Diff Flange so that you can put the DS back in the same way.
Then disconnect the DS from the rear diff (4-17mm bolts/nuts).

Drop and slide the DS towards the back of the truck; the whole thing slides right out. Take out the c-clips (4) holding the u-joint in place.

Knock the old u-joint out with a socket (my 17mm impact worked for me) and a BFH stopping when the Journal bottoms out. If you go too far you bust the caps making it more of a pain to remove.

Once it's bottomed out, if the one side hasn't fallen out, grab it with a vise-grip and then hit the vise-grip with a hammer...should pop right out. Hammer out the other side with a smaller socket. Vise-grip/hammer...
Clean out the ears of the DS and Fkange removing any rust and/or debris, especially the groove that catches the snap-rings.
I put some tacky grease (RCV) in the caps so the needle bearings don't shift when I hammer them in and anti seize in the ears...especially the groove that catches the snap-rings.
Press the new one by tapping the caps with a hammer, finish with a the socket.
Put in the 4 new c-lips that comes with the new u-joint.
Slide the slip yoke back in careful not to damage the TC seal and connect to the diff.
Torque the bolts to 58-65 ft-lb.
Done.

If you have a press you can use it making sure you don't over press. I made the mistake of using one too much and busted the cap making it more of a pain to remove.
I know most folks prefer the socket/BFH method even when they have a press. Some start with a press to break the u-joint out of the rust and finish with a socket.

You can get greasable or sealed (non greasable) u-joints. I prefer sealed; I think they last longer. It is debatable and ether one will do the job and would be correct.

Great thanks everyone. I am guessing both ujoints will be the same size? My local NAPA was able to cross reference the 1310 to their part number.

yes, the u joints are both the same size for the rear shaft and also the same size for the front.

BTW, if you you get greasable joints you will probably need to pick up a needle grease gun fitting. make sure you don't get a style of joint with the grease fitting on the end of the cap of the joint. it could be sheared off when off road when used on the rear of the driveshaft.

Thanks again everyone who replied! I got both joints at napa for under 20 bucks and just finished changing them out. One of the caps on the rear u-joint was broken in two with a piece missing. This was the cause of the vibration I was feeling between 13 to 20 and 30 to about 55. Thanks saltus440 for the size and Tom for the right up!!