u joints

[BIG CHEVY]

can u tell if a u joint is bad while still on truck? mine are unmovabe in respect to they move perfectly to the eye with the rest of the driveshaft. i get the clunk......dont wanna replace if they are good. how do i tell?

[bake74]

     You need to go under the truck and grab one side and move it back and forth, if there is any amount of play in it, they need to be replaced, that would cause a clunk when spinning driveshaft.