Switching to M1 diff oil.

Aug 4, 2003
I know this should be a simple drain and refill operation, but is there anything special I should know before proceeding? Don't have the FSM yet, but owners manual says 90w or 80-90W. The only M1 I could find was 75-90w. I assume this will be OK. Should I flush them out with anything (to get old dino out) or just drain and then fill until it drips out the fill hole? Do I need anything more than a 24mm socket and a pump? Sorry for the "dumb rookie" questions. Thanks!



On the way there
Mar 15, 2003
Sacramento, CA
Make sure you have new crush gaskets from Toyota. The gaskets they sell at NAPA for this don't seal right. Undo the filler first, so you don't have an empty diff and no way to fill it up. Make sure you use a 6 point socket. The Mobil 1 gear oil is good stuff. If the old oil is milky, that means it is contaminated with water and I would do a quick change or two with cheap gear oil (Coastal from AutoZone meets the specs and is really cheap) and then add the good stuff. If the oil gear oil looks uncontaminated, just dump in the new stuff directly. Don't forget to do the transfer case as well.
Aug 8, 2003
Also, don't have a heart attack when the rear comes out looking nice and the front diff comes out nasty. It's typical for some gear oil contamination to have taken place on any 80 front diff.

If this is the first drain/fill, you'll have several grams of shavings on the rear diff magnetic drain plug - some as big as a child's fingernail. Normal. Rare on the front.

Finally, if some moron has tightened the front diff fill plug too much, use a 6 point socket as noted above, coupled to a breaker bar and use the 80's jack to push up against it. It WILL come off this way - absolutely, positively off.

Of course, do this immediately after a long drive that gets the fluid warm and particulates suspended so they flow out. I've been using the Mobil 1 75-90 for about 100k miles now, and my diffs are notably quieter than others are.


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