I just finished replacing my u-joints with a 12 ton press I purchased. when I was done I noticed that they were very stiff and a little difficult to move. I pressed them back out and they spin freely. Press them back in and now one is good and the other is stiff. Whats going on??

 

The ears that you press the bearing caps into are being closed up every so slightly. When you get the ujoint in, get a punch and a big hammer, and give those ears a good whack to open them up again. If you leave it as it is, the new ujoint will fail very quickly.

 

Is it something I'm doing wrong? (Just for my knowledge in the future) Or is it just one of those things that can happen no matter who's doing it?

 

It just happens, I've never found a way to avoid it.

 

i am afraid to mess up the alum shaft by pressing on it to change out the u joints

 

And if you take it to a shop, they're gonna press on it to change the u joints. There's no other way to change them.

 

Yes, this is the way it goes. Hammer around on it until it loosens up. All the bearings need to rotate easily.