Additives and synthetics dont mix very well. You get less lube on the hot parts of the diff because of this. The hotter a diff gets the less the oil wants to stick to it. Diff additive helps the oil stay on components when hot like clutches. Since the additive doesnt mix well with the synthetic you get less lubrication. At least I think thats right. Thats how it was explained to me at work. I questioned our head of Chrysler training about synthetics in our vehicles from the factory. We use a different type of clutchless diff now. He suggests good old diff gear oil and additive for any of our older models even if they came factory with synthetic. The only Chrysler you have to watch is our Jeeps with the Quadra-trac. They take no additive and synthetic. Very cool diff set up. Google it.
As Darren said and... The extreme lubricity of synthetics doesnt allow the gears to wear together( if they are new) as they are supposed too in order for them to break in properly.
hmm. that all makes sense. however my gear is used and already broke in, just the posi/clutches are new. Does this change the usage of synthetic? right now I only have the Royal Purple installed, no additive.
ive seen many gear failures due to synthetic gear oil. now i realise that not all syn. gear oils are the same but in my vast differental experience no synthetic gear oil protects the gear set as well as a natural base gear oil. at work we use schaeffers gear oil http://www.schaefferoil.com/ its really sticky. i feel all your doing with puting synthetic gear oil in the diff is wasting money. what ever gain in power your susposed to get with the synthetic is lost by the gear set wearing out early.
