how to check u joints

try to rotate them by hand, if you feel any slop in the joint, it's toast. That's about all you can do without removal.

Another question is how old are they? If an F150, the last time they use u-joints in them was 1996. If so and you have OE, it might be worth replacing them, especially since Ford does not put grease fitting in them.

I should have said front u-joints on the axle. Drive shaft naturally has them front and rear.

If you got it cheap enough, its not an issue.

does the truck have a suspension lift kit on it? have you checked the transfer case fluid level? I've had a few 4x4s over the years that had to back up to get them out of all wheel drive, none of them I will add had a good old fashioned shift lever' The problems we get because we are too damn lazy to shove a lever, and lock in some hubs.

Whitelightning

Remember, switching from 2wd to 4wd you add a sh*tload of moving parts that will make the drive train a lot more noisy and will have more vibrations.

Are you sure you know how to use 4wd ???? not trying to be an ass but you might be chasing something that's normal

NEVER/EVER on hard surface , this will cause binding on the drive train and cause clunking etc.

Maybe you want to spend $75 to $100 and let somebody (dealer/4wd shop) check the 4wd system, that's cheaper then throwing parts @ it on parts it doesn't need

13 years is showing more than 74k miles. Sounds like it's working fine, just asking for some grease maintenance.

Ok that rules out that thought, if the diffs aren't shimmed at the spring perch to correct the angle between the drive shaft and the pinion when lifted, you can get binding and vibration.

Whitelightning