Is this u-joint or output shaft leak?

[new2yukon]

I was thinking this was output seal but further review and more miles yields these pictures.

It all looks dry right at transfer case so I "assume" this is u-joint grease?

I wiped it off on the black emissions box and its thick.

Am I correct? Bad u-joint?

 

[ks03]

The front yoke can let fluid seep through, lets it out right in front of the ujoint, can kinda see a darker 1” or so diameter ring. I replaced probably 2 or 3 yokes ever for this back when they were under warranty, (I might also be including nnbs) and could cause a drip. I’m guessing that 20 years in, this is leaking extremely slowly. I’d say check you transfer case fluid, and then optionally clean up everything thing else to confirm where it’s coming from.

 

[OR VietVet]

What M said. Why there is a hole in that yoke that allows the leak is beyond me. I would be tempted to remove shaft and clean as best as you can and fill the hole with something.

All that buildup is not u-joint grease. That much grease would have allowed the u-joint to dry and be bad and noisy already.

 

[new2yukon]

That buildup on the black emissions unit is relatively recent. So it's progressing "nicely" and coats my floor panel as well. It is getting worse.

I'll check the trfr fluid. And decrease the joint.

So is the hole something that is a clear shot to the trfr case that simply allows seepage? I don't understand the hole issue.

 

[ks03]

There are different design yokes, some are supposed to be sealed, some have a vent hole in the center, and I believe the shaft has another seal somewhere... All the ones I ever replaced were ones that were supposed to be sealed, only gm approved fix I ever heard of was just replacement, but if it was mine, I’d probably drop the shaft, cleanup the back side where it’s coming out with brake clean as well as I could and smear a little jb weld over the area.