I have a 1998 f-150 super cab 4x4 with a 6inch lift and 3 inch body lift with 37' mud grappler tires.
My question is upon acceleration or in reverse I hear a loud clunk coming from where i believe as the driveline I know I have some axle wrap because I don’t have any traction bars but I am unsure why it just started. This has never happened, it only sometimes occurs, any ideas or inputs would be greatly appreciated. By the way I just had 4:88 gears installed about one month ago but I don’t think that would be the case.

 

I would start with the u-joints, they may be totally worn out and they are cheap and easy to start with...

 

Take a look at your U-bolts that hold the rear springs to the rear end.
They may be loose. If you have lift blocks under the springs and axle wrap, there is a chance that they have worked loose.
Just something to look at.

Scottie

 

Does anyone think that this coincidently coincides with the gear swap a month ago???????? More gear means more torque on the driveline. Yes, you need to double check all rear axle connections, but you need to realize that the bigger gear almost doubles the amount of torque to the axle. With reverse always being the lowest gear, that would add to an "axle wrap" situation causing a "clunk"

 

My rig had a terrible amount of axle wrap,so bad that you couldn't spin the tires on pavement without feeling like to rear end was gonna fall out.I used a set of BDS rear leafs to replace the "less than ideal" stack of blocks in the rear, and it's alot better.