I'm dealing with a clunkity clunk in the drive train that speeds up when you accelerate and slows down when you slow down. It's especially noticeable when slowing down in neutral, slower speeds, and kinda lugging along. I thought I had it figured out when the rear axle seal leaked. I replaced the rear bearings and seals and put fresh diff oil in it, but it still clunks. I pushed around the drive shaft around the universal joints and they feel pretty tight. The only place I get a similar sound is behind the universal joint where drive goes into rear diff. I've jacked it up and spun everything and even run it and can't get it to replicate. It's only under load that I get it. Kinda hard to get under the truck while it's moving hahaha.

 

It could be the backlash between the pinion and ring gear. It’s pretty easy to adjust when the diff is out. I have this job on the list for my truck.

 

Thanks Melrose! I may throw a locker in mine at some point and will investigate then.

I'm not certain, but having just redone the front brakes and having to tear apart the 4wd hub may have solved the issue. The front wheel bearing nuts were extremely loose. I had tightened oneside because an alignment shop said they couldn't align it due to the wheel bearing being loose. Well the other side was WAY worse! The little locking washer wasn't even bent over the nut to hold it tight. The nut came off by hand I literally touched it and it loosened up. Needless to say I think the front wheels were wobbling which probably is why the brakes were so bad looking. Pads were hanging over the edge of the rotors and rotors had terrible rust streaks and wear. She brakes great now and I have to drive and listen more closely but on the first drive yesterday I could almost swear that there was no clunk. It may have just been the bearing and nut spinning against the lock tab washer inside the hub Yikes!!!!!

 

Ahh wishful thinking hahaha. While the brakes are working better than ever, and the front end feeling nice and smooth, the clunkity clunk is still there in the drive train/rear diff. I'm thinking about having the wife drive and me hang out the back with the GoPro on a pole and film/see if we can narrow down where it's coming from.

 

So sometimes it’s simpler than ya think. Atleast first and second test drive are sounding good.

I greased every zirk on the drive shaft deeply and it seems to have taken the slack out of the system.

Ive greased before with no difference but have always been nervous around the fitting that pushes the driveshaft out. Well this time I just pumped till I got old grease coming out the slip and it really seems to have quietened down dramatically if not completely!

 

Ahh well now I'm really confused! So I drove it twice after greasing everything up and I couldn't get the sound to happen, no matter what I did that normally would. A couple days later it's back and pretty much just as noisy. Maybe it needs a second round of grease in the back end, but I'm thinking either a few teeth on the gear are gone or like you said Melrose it's probably the backlash spacing in the diff!

 

Can you grab the driveshaft by hand and twist it and make the sound? See if you can locate it that way. My excessive backlash shows up.