Most aftermarket ones are grease-able. You do not need to grease them very often but it sure is nice to be able to do it rather than replace them.

As far as front or rear goes, which one is bad?

 

Don't know...I had a mechanic look at the problem and said that the u joint needs replacing. The suspected sound is coming from the rear axle area.

 

While it's not a super challenging job to do at home, it's also not too expensive to have done at the shop.

You may elect to just have it corrected. It's not an exact science, but it does have to be properly centered within the cups. If it is not it will wear prematurely and you'll just end up doing the job again. There are a lot of youtube videos on how to replace them. Just make sure you don't watch the videos with a guy who looks like he has had too much to drink and hasn't completed high school. Not to say there is anything wrong with that, but those videos tend to leave out important parts of instruction. Things like, don't forget to make the original relationship between the drive shaft and the yolk. I've always been told it should be reassembled the way it was prior to removal-for balance concerns. Some will argue that and say it's not important. But it takes 3 seconds to mark the parts and it's not worth the gamble to not mark before removal.

 

Are colly u-joints held in by plastic like s10's? If so you won't be replacing it without a lot of heat.

Also, 08Canyon makes a good point. I always mark my shaft/pinion with a grease pencil so I know it's oriented the same. Might not be necessary, but certainly doesn't hurt.

 

Yes they are held in with plastic, you are wrong that they can't be replaced without using heat, I did one on my truck and one on my bro in laws Colly without heating them up. Nice big bang when it lets loose but it will let loose without heating them.

 

I did some plastic seated ones on a Silverado just by pressing them out with a vice. It never occurred to me to heat them.

What are you doing with the heat?
Are you melting / burning the plastic?

 

There is a post in the appropriate forum about this. It just softens up the plastic and makes it easier to press out. I would admit that if I have to do this again, I will get a small propane torch and heat up the yoke, but it isn't neccesary to do this. The plastic is there instead of the retainer clips. The new ones will use retainer clips, and there are grooves in the yokes for the clips. I wonder if official GM Ujoints use clips or if the plastic nubs are used? I have just used autozone Ujoints.