Not really hot rod related but I'm looking for some input. I'm changing all the gear oil in the diffs and tranny and t case on my 2009 Toyota Tacoma. and the manual calls for 75-90 but all I can locate at any stores is 75-90 synthetic. always heard that you can't use synthetic after using regular as it damages seals? thoughts ?
Damaging seals is a load of crap it will clean the hell out of anything you put it in thats the problem with older engines. To make it short unless your 2009 sealing system has already been compromised and grime and sludge is keeping it from leaking it will be fine
I think it's more important to make sure that your gear boxes need GL-4 or GL-5 oil. GL-5 oils tend to contain sulphur-based additives, which can deteriorate copper alloys.