Yanked the axle out of the truck. Surprisingly everything came loose on a 10 year old salt belt GM. Drained the fluid and saw the c-clips on the axles and this is what I saw. Blue. Blue means hot. Hot means weak.
Pinion gear has a little odd wear on it but the ring gear looks new. Original plan was to put in a new diff, bearings and seals and rock in for another 10 years. This has me wondering if I should replace the axles too?
What would the hive do? This truck is a long term ownership deal so if it needs something it gets it. Period. My thinking is just so it all once and be done.
I'm having a hard time imagining what could overheat the end of an axle, but not kill the side gears. I'd bet what you are seeing is the remains of the original heat treating. If your oil was old and E36 M3ty, you wouldn't be able to see that. Quit cleaning E36 M3.
Blue is also a side effect of heat treating. If the side gears and the clips themselves don't show any signs of wear then I wouldn't worry about it. It's hard to tell from one picture but those all look like pretty new parts from here.
Looks like the parts were case hardened maybe?
I'd be inclined to agree that's hardening, I think axle shafts are induction hardened so the whole thing isn't heated. The only way I can see the shaft getting hot like that in use would be a long one wheel peel, and then it'd probably be all one side and you'd see color on the side gear too.
Definitely heat treating.
makes sense.... the replacement pieces I'm seeing are showing the same coloring.
Yukon lsd, bearing kit ordered from Amazon.
SVreX
MegaDork
1/21/17 4:20 p.m.
I was really afraid to open this thread. 
In reply to SVreX:
I laughed quite loudly at that, and then remembered the worst case I ever had, back when I was 20 or so.
Ouch.
The cure was good, though.
Hopefully your cure didn't include anything around 3.56...
3.56? I could only dream. Staying with the 3.23. LOL. Some day I'll stuff a 6.0 in there and test my theory on fuel economy and towing power.
