I'm getting a CLUNK when coming to a stop with my truck.

If I shut off the overdrive while coming to a stop it doesn't do it. Or if I manualy shift it down a gear.

I read on here it could be a U-joint or the yoke or something and maybe something needs greased.

Anyway I crawled under the truck and it looks like I need a special socket to remove the 4 bolts holding the driveshaft to the rear end.

What type of socket it this?

No grease fittings on my U-joints.

Any idea what's causing this CLUNK as well?