New Gears..... Update!

Ben... the gear shop that did the work said I do not want to put synthetic oil in my differential. I didn't ask why because he's been doing gear work for many, many years. His grandpa was doing it when I was a kid.

If you Google why you shouldn't use synthetics in a rear differential, there are many reasons but the biggest reason is that using synthetics will void the warranty from the gear manufacturer. I don't run synthetics in my GMC because of being high mileage.

There's a lot of debate over using mineral oil based vs. synthetics. I don't know if there's any right or wrong answer but I do know that cars have been running a long time on oil in the differentials. Maybe the biggest reason to use synthetics is so the "non-oil" companies can get a piece of a very big pie. ;)

BenK wrote:
Go with Kevin's advice, it is sound and make sure synthetic, as it his higher both temp range and ultimate temp allowed

First number is the lube's viscosity at room temp (how thick/thin in reference to water) and second number when it gets up to working temps

By design...all gearing lube is supposed to have enough viscosity and film strength to coat the gear teeth so that there is no metal to metal contact between gear teeth faces....but poop happens and they occasionally do go metal to metal

Why having the correct viscosity index is so important and again, synthetic. It has higher spec both in film strength & temp range

Stay away form the very good exotic anti-friction lube additives if you have clutches in there (LS, G80, etc)....to slippery and will ruin those clutches