Differentials need servicing - Need Advice

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May 18, 2009
My recently-acquired Tundra 4X4 has never had the gear oil changed in the differentials or transfer case. The manual calls for API GL5 75W-90 gear oil. However, a guy at a very reputable high-performance 4X4 shop said he puts ATF in a lot of differentials. Subsequent Googling has indicated that others do this, too. But it doesn't seem widespread. He said 75W-90 was "old school." As I am going to do this work myself, I am trying to decide whether to just go with what the book calls for or use ATF. Will ATF be harmful if I change it every 30k mi? Will there be any benefits in terms of economy, performance or MPG? Thanks.
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I would be sticking with the 75w90, I personally would not put ATF in a differential as gear oil and ATF are two different fluids made for different purposes.
There is no way ATF would protect the differentials. The differentials are the highest stressed component in a vehicle as far as the load and the oil required to protect it. ATF would be harmful in a hypoid gear set which is what is in your Toy if you changed it daily.
ATF is too thin to provide the protection you need. You'll trash your bearings and gears. I would use a full synthetic 75w90 in the front end and transfer case. I would consider a 110wt or a 140wt in the rearend. I would NEVER use an ATF when a GL5 gear oil is required. I would avoid 'the guy' for any recommendations.
ATF may be used in some combination transmission/differentials on FWD vehicles. It is not the right fluid for a diff, no matter what. I'd avoid it like the plague.
Thanks, folks. To be completely fair to the guy at the 4x4 place, he said something to the effect of "many people are putting ATF in their differentials" and then said he'd have to check to see if it would work on my particular vehicle. But the dude was on the level as far as I could tell.
Absolutely do not put ATF in a differential calling for a GL-5 gear oil. There are no benefits, only the very high risk of ruining your diff in short order. Use what Toyota recommends. There are many high quality gear oils available for your Toyota Tundra diff and transfercase. I personally like and use Amsoil Severe Gear which comes in 75W-90. They also make an 80W-90 which would work well, too. Both are synthetic. You don't have to use a high quality synthetic like Amsoil. Since it is not a lot of fluid that is changed often, I like to use the best I can find, but really any name brand stuff that meets the GL-5 spec and is 75W-90 or 80W-90 will work fine. If you have a limited slip, an additive may be needed to keep it from chattering. Perhaps he was talking about putting ATF in the transfercase, which IS a common practice and some units do call for ATF there, but not Toyota.
Thanks. No LSD. Since I am going to need about 6 quarts, I figure I will just get whatever is on sale or the cheapest and try to change it out every 30k mi -- assuming the truck lives that long.
never heard of that. are you sure he was not talking about the transfer case instead?
Wow, that's some strange advice. It's possible your differential would last a few years on ATF if you don't tow anything, and you will likely see improved fuel economy. I wouldn't try it though.
I have an early model Tundra (almost 10 years old now). There is a sticker on the front diff that says to use only 75W-90 GL5. That's what you should use. Same for the T-case. You're supposed to use SAE 90 GL5 in the rear, but 80W-90 may be used if temps are anticipated to be below zero degrees F. That's because the rear diff is where most of the high heat and extreme pressures occur. The only advantage to using ATF in any of these components is fuel economy. But it surely won't help protect them any better, and most certainly would shorten their useful life. Over the years I have used many brands and viscosities of GL5 in all of these components. Here are some lessons learned: 1. Don't overfill any of the components. The front diff and t-case have breathers that will sling gear oil all over your engine bay. 2. Get washers for all of your drain and fill plugs (some are crush; some aren't) before you get started. 3. Always take the fill plug out before you remove the drain plug (you want to be able to re-fill the component after you drain it!). 4. If you use a synthetic gear oil, check for seal leaks often. If you get one, go to the Auto-Rx website and follow the directions. 5. Use the 4X4 often (at least once per month) to lubricate all system components and seals. Remember to stay below 60MPH and avoid sharp turns on dry roads while doing so. My current setup: front diff and t-case- 75W-90 Valvoline GL5 rear diff- LE 1605 SAE 110 GL5
I think that either you mis-understood him, or he was mis-informed. It is not unheard of, to use gear oil in place of ATF in transfer cases or manual transmissions, where ATF is the specified fluid. Although I do not subscribe to such practices, some people are stuck in the "thicker is better" mentality. This in mind, I suspect he was referring to using gear oil in place of ATF in such applications. Perhaps he mis-stated the concept, and confused the direction of application. But I've NEVER heard of using ATF in place of gear oil in a differential for general automotive serive. Absolutely a bad idea. It is possible that some of the extreme off-road vehicles do this as a practice. I'm not much into the off-road sports, so I'd can't comment for sure. Perhaps the ultra slow speeds and extreme angles of rock-crawling might lend themselves to a "need" for a lighter oil that would flow a bit better; I truly don't know. But for everyday "normal" vehicle use and serivce, ATF does not belong in the diff's. If you're looking for premium performance and servicability, consider a "synthetic" GL-5 fluid; you'll get a bit better temperature performance, and much longer fluid life (well past 30K miles). I'll let the others argue which brand is "best", but any GL-5 rated fluid will suffice; some out-perform others. If you are committed to changing diff fluid every 30k miles or less, even dino fluids would work well, as there are plenty of good brands to choose from.
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If my truck calls for 75W-90, would it harm it to put in 80W-90 instead? (It much significantly less expense and available in gallon containers where I shop.) If this is a significant difference, please let me know.
My Wife has a Sequoia its got be the same as the Tundra We bought it used it has 60K on it. I am going to change the transfer case and the diffs. I did not know what it takes. In My Silverado I put Amsoil Sever Gear 75-90 in the rear and 80-90 valvoline dino in the front diff. I will probably just put Mobil1 gear oil in the Seqouia and the transfer case.
 Originally Posted By: Arbuckle
But the dude was on the level as far as I could tell.
Doesn't mean he isn't stupid. Use a 75W-90 in the transfer case, and either a mineral 80W-90 or a syn 75W-90 in the rear. If you run heavy & hot you can use the 75W-110 in the rear, but I wouldn't use that in cold winter areas. I prefer a synthetic, especially for winters. My 4wd is used for snow driving, not desert driving...your mileage certainly will vary. Did you know that the driveshafts have eight grease fittings? Two on the front and six on the rear. Strange noises are the result of a dry spline on the rear drive shaft. As said above, always loosen the fill before removing the drain, so you know you can get oil back in.
Probably a bad idea to run most ATF's in that differential. But I'd be willing to bet that Amsoil ATF meets or <i>exceeds</i> the spec for 75W90 GL-5.
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