How do I know if my U Joint is needs replaced?

[philipcoble]

I have a '15 Chevy Duramax and when I back up or stop, after a couple seconds I hear thud from under the truck. I'm wondering if it is the U joint? How do I know if its bad without tearing it all down?

 

[stutaeng]

Get underneath and try to rotate the driveshaft. It's better to drop/remove the driveshaft and check each end individually. There should be no play in the joint.

How many miles do you have on your truck?

 

[454cid]

Wiggle it, but make sure there is no tension in the drivetrain.

 

[Supercharged111]

You need to remove the driveshaft to feel them individually. You'll know it when you wiggle them around. I had one that failed and squeaked at low speeds as it oscillated back and forth. That's what clued me into its failure. My G80 diffs are worn out and have slack in them. That's where my clunks come from.

 

[philipcoble]

Thank you all for your input, it's the shorter drive shaft of the two and it does move a little back and forth so I think it's on it's way out. It rotates just fine tho. The main drive shaft is good, no play at all and snug. Everybody have a Happy Thanksgiving Ya'll!

 

[Schurkey]

1. Your truck is not a GMT400.

2. Shorter of the two??? Do you mean the driveshaft for the front wheels, or do you have a two-piece rear shaft with unequal shaft length? If this is a two-piece rear shaft, it's really "one driveshaft with a hinge (joint) and hanger bearing in the middle".