Gear oil breaking down?

[SUX2BU99]

Is it normal at all for rear gear oil to break down in hot weather under heavy use? We have had a week here of 95+ temperatures and any time I romp on my truck and do a WOT 1-2 gear change (twice since the new gears and after putting over 250 miles on them), my rear gears make some more howl than usual but then settle down to more or less where it was before. It's like the oil cools down some and things quiet down. It has what the rear end shop put in there last week when they put in the new 3.73 gears. I've put about 400 miles on the gears and I figured I'd change the oil soon maybe with Castrol. For some reason, I'm not entirely confident in whatever kind of fluid they used.

[VileZambonie]

Do a gear tooth contact pattern analysis.

[SUX2BU99]

True, that's obviously the best thing to do, provided I have the gear marking 'paint' and the experience/knowledge to know what I'm looking at. Yukon has online install instructions and shows pictures of proper gear contact so maybe I will try that when I do a fluid change. Is the gear marking stuff a specialty kind of item? They showed me that at the shop when my previous R&P was wiped out and it was a yellowish color that they painted on with a brush.

It's just odd to me what I get a louder howling sound after getting on it, and only for 10 seconds or less at WOT with a 1-2 shift, and then it quiets down some as the oil cools. I've never heard that before.

[VileZambonie]

Are you sure it's not the trans?

[78 Chevyrado]

The gear marking stuff is called machinist's blue

Here's an example
http://www.highlandwoodworking.com/browseproducts/Starrett-Machinist%27s-Blue-Dye--4-oz..HTML

[VileZambonie]

layout dye and dykem won't work very good nor will prussian blue. Gm has the best gear marking compound.

http://www.ringpinion.com/ProductDetails.aspx?ProdID=4540

[SUX2BU99]

Rear end shop said the same thing when the previous R&P went south. Nope, it was the rear end. My trans has always worked great. It shifts hard yes, but the howl is most certainly rear end.

I'm trying not to dwell too much on it. I've been told that numerically-higher gears can be louder sometimes.

I read that good ole white toothpaste can work in a pinch for gear marking. Ever hear of that?

[VileZambonie]

White grease will work too but gear marking compund is the best. If it was set up correctly it should be quiet no matter the ratio.

[SUX2BU99]

Crap man, that's what I keep thinking too.  I got a 1 yr warranty on those gears and I think I'm going to do some 'testing' throughout this next week and see what happens. Why the heck does this have to be so bloody complicated? Rhetorical question, I know.  Plus their location totally bites as I have to take a day off work to get to/from there. Blahhhhhhh