Transfer case oil - 80W-90 okay?

Royal Purple syncromax is LF type. The reason why the transfer case fluid is specific is because this transfer case as well as some GM transfer cases use soft metal (copper, brass) bushings in the syncros. LF type fluid is designed with low phosphate levels that will not deteriorate the bushings, unlike regular gear oil.

 

I changed the oil in the 2 diffs and transfer case about 2 weeks ago.
Used royal purple 75w90 in all 3.
After roughly 500 miles or so of driving I've notice a 1 mile per gallon economy.
Never changed my driving habits either.
So the $100 worth of oil will or just did pay for itself.
Plus the added benefits long term.

Front diff oil was dark, but not milky,...t case and rear diff were clear...
Truck has 30k miles.

 

Yellow metal sync rings have been in transfer cases for decades. The erosion of bronz sync rings only occurs in situations where you are shifting constantly, and even then it’s rarely a problem. Unless you are constantly shifting from 2wd to 4wd and back all day long, you will never experience this. It’s a problem specific to MTs.

The issue centres around the sulphur lubricant in GL5 oils combining with the bronze and making a harder surface coating, that may rub away slightly quicker during impact shifting. This isn’t going to be an issue in a transfer case, but hey.....what do I know? The 2nd Gen tacos had bronze components and used normal old GL5 80W90.

 

Maybe a GL 4 oil would be appropriate.

 

Redline MT85 is a GL4 75w85 oil that is safe for brass synchros . They claim on there website that it is a direct substitute for 75w and has two Toyota part#s listed.

 

I'm about to do the diffs, trans, and transfer case... Missing my ranger that used ATF in the gearbox and xcase