I was just wondering what are characteristics of u joints going out? Such as drivetrain rattling at speeds above 45 mph with full throttle.

Thanks

 

In the later stages you'll hear an almost constant humming going down the free way and even in parking lots. Get under the truck and grab the driveshaft with both hands while the truck is in gear and the parking brake on (engine off of course). Try to rotate the shaft in both directions. If it rotates at all in either direction you need to replace the U-joints.

 

They'll also make a "clunk" when changing from accelerating to decelerating, or from stready speed to either one. Some U-joints have Zerts for greasing, and sometimes that'll solve the problem, but usually by the time they start making a noise you can hear while driving, it's too late for lube...