Switch to synthetic..chevy 12 bolt posi

[g356gear]

Any consensus on whether it is a good idea to switch to synthetic in my 12 bolt posi rear end if it has had regular gear oil it's entire life since new?? Thanks.

[chicane67]

If it's an EATON clutch limited slip posi... DO NOT use synthetics.

Not to mention that synthetics in the 75-90 weight are useless in performance applications... unless the differential fluid is going to be changed on a regular basis... like it would be in a race car.

[big gear head]

I have used Amsoil synthetic oil in the rear ends that I have built for about 12 years with no problems. I've built a few hundred rear ends in that time. The new Eaton Posi comes with a paper that says not to use it, but I haven't had any problems with it. The old Eaton had steel clutches in it, but the new Eaton has carbon fiber lining on the clutches. GM uses these same clutches in the truck Governor Lock and ALL of them come from the factory with synthetic oil. It's really up to you. Some synthetic oils are good and some are not.