2015 F150 XLT SuperCrew 3.5L 4X4 Locking diff

I've noticed for awhile now that I often get a clunk that sounds like it's coming from the rear diff. Best way to reproduce it is if I'm going up an incline, if I let off the accelerator for a second then back on it again I get a clunk. Most of the time even on flat ground if I let off accelerator, tap brake just slightly, then back on accelerator I will get the clunk. It's not super loud but loud enough. And, I don't have to stomp on it, just like if I realize I'm going too fast I let off the accelerator, tap brakes, then just press it again normally I get the clunk.

I've checked the U-Joints, seem tight. With truck on lift if I just go back and forth with rear wheel there is some play but I can't duplicate the clunk.

I did a drain and refill on rear diff, and transfer case, which did not fix the issue.

Any ideas?

 

If you have a one piece driveshaft, it is common for the lube in the slip yoke to dry out causing the driveshaft to clunk rather than slide.

 

Ok, I remember when I worked as a lube tech at a Chevy dealer in the 90's there was a problem with the Chevy 1/2 tons doing the same thing and that was the fix for that, pull the yoke out, smear some grease on it, and put it back together. Makes sense now that I think about it.

I'll give it a shot soon as I can get the lift and me free at the same time.

Thanks!

 

Do you have the super 8.8 or 9.75 diff? I just had to replace my super 8.8 a couple weeks ago. Was getting clunks when turning. The gears and case were destroyed. Upgraded to an Eaton tru trac and it feels so much better.

 

Pretty sure it's the 9.75. I had the cover off a couple months ago and everything looked good inside.

 

I had a similar issue. This past weekend I pulled the driveshaft and greased the spline, no more noise.

 

That fixed it. Thanks for the help.