I've reached my 1000mile mark for breaking the rear end in. I'm about to dump the 2.5 qts of 80-90 gear oil in and mistakenly bought synthetic. My original plan was to dump 2.5qts of dino oil + the bottle of GM additive in like the tag that came with my rear said.

Can a synthetic gear oil (Valvoline 80-90) be used and if so should I leave out the bottle of GM slip additive? My instict says "go return the 3qts of synthetic and buy dino, then add the slip add bottle).

Input appreciated.

 

you can put the synthetic in, its good stuff, read the bottle though to see if it does include the limited slip additive, if it doesnt say anything then just add the extra bottle of it.

 

AC hey i know u lol my moser says DO NOT use synthectic for some reason so i'd call strange just to double check it always safe then sorry

 

I have been using Amsoil synthetic oil in almost all of the rear ends (probably about 400) that I have built over the past 11 years and have had no oil related problems with any of them. I have not seen any synthetic oil, except the Amsoil Severe Gear, that worked without the additive. If you have Valvoline then I recommend using the Ford additive. GM is good too, but don't use any of the additives from the auto parts stores.