Popping in rear end at low speed

[papastruck]

Ever since I got the truck, after you drive it for a while, there's a popping sound at very low speed, especially when backing up and turning. It sounds like someone beating on the rear end with a rubber mallet. It seems to be on the input side of things, meaning the tempo of the popping picks up faster than actual wheel acceleration. It pops hard enough that you can feel it in the cab, and while I'm not sure it's getting worse, it's pretty alarming as it is. It's got plenty of fluid in it. Based on this, the rear end is a Sterling. Does anyone have any thoughts on what it could be or a course of action for diagnosis?

Thanks in advance.

 

[GenLightening]

Have you checked your U joints? Any rusty dust coming out of them?

 

[papastruck]

I've not pulled the shaft off, but they feel tight and look like they've been getting grease. It's occurred to me to either pump a bunch more in and see if it changes the tone any, or just throw a new set at it since they're cheap anyway. I guess the reason I wasn't really eying them is because they're not making any of the usual highway noises.

 

[GenLightening]

Are you running a limited slip rear end? The noise while turning could be the plates grabbing (possibly galled?). And since it's 4X4, make sure it's not coming from the front axle U joints.

 

[papastruck]

Solved quite a few mysteries on that truck, but not whether the rear end is limited slip. Did I miss something on the VIN? Front is a Dana 60 open from what I can tell on the VIN. Any other way to tell if it is LS without pulling the cover off?

Front axle has been disengaged since winter, though, yeah, the noise did inspire me to check that, too.

 

[GenLightening]

Jack it up and spin one wheel, if the other spins in the same direction it's a LS. If it spins the opposite direction, it isn't.

 

[papastruck]

Jack it up and spin one wheel, if the other spins in the same direction it's a LS. If it spins the opposite direction, it isn't.

Cool thanks.

 

[MIDNIGHT RIDER]

It reads like a typical case of limited-slip issues.

Although it may not permanently fix whatever is going on, adding a tube or two of "limited-slip additive" and immediately driving through a BUNCH of figure-8s to get it all worked into the clutch-plates will cure the problem for a while.

 

[zebrabeefj40]

Someone could have also installed a locking diff like a Detroit or Lockrite. Those make a popping/clackclackclack noise when turning at low speed... They'll even go BANG once in awhile. Alarming but yet normal behavior; IF that's what is in the diff. Pull the cover and take/post a picture. I'm sure someone will know what's in there.

Nick