ATF in differential cases?

[Doubt Incarnate]

I havent been able to find anything definitive on this. I know FWD transaxles just use ATF in the entire setup, differential and all. Why cant we run ATF in our differentials? It has to have friction modifiers since the transmission has its own clutches and bands, so it shouldnt give a limited slip any trouble (theoreticaly). I'd have to imagine the lighter weight, thinner viscosity, would benifit mileage, power, 1/4mi times, etc.

 

[dogfriend]

IIRC, differential lubes usually have EP (extreme pressure) additives to protect against gear wear. ATF doesn't have this. However, Ford (and probably other manufacturers) often recommend ATF for manual gearboxes - my Ranger with the M5OD called for Mercon ATF.

So, you could try to run ATF experimentally, but the engineers who designed the differentials recommend a different lube. Personally, I would look for a high quality syn gear lube, but I am looking to maximize life rather than fuel economy or power.

 

[celly]

ATF is fine in your transfer case, but I don't think it's recommended for your differentials.

 

[4x4junkie]

Yeah, too much contact pressure between the gear teeth (both ring & pinion, and spiders) would break down the thin ATF, causing metal-to-metal contact and excessive wear (possibly scoring the gear teeth as well). The pressures are much less in a transmission, which allows for it's use there.

 

[Doubt Incarnate]

how does fwd get away with it? and you cant use weight as an excuse because some of them are hefty, like caddilacs, bonnevile, some buicks and olds. im sure minivans are up there too. the fwd units are all pumped, filtered, and cooled. what if a system was rigged up to pump it through a filter and cooler before sending it back in?

 

[nitro71]

Why even do it.. Use what Ford wants you to use. Lubes are cheap at Walmart.

 

[Doubt Incarnate]

I'd have to imagine the lighter weight, thinner viscosity, would benifit mileage, power, 1/4mi times, etc.

thats why. maybe some good old fashioned "wonder" and tinker-lust. im one of the guys that took every toy i had apart when i was a kid.

 

[dogfriend]

Redline makes a "Lightweight" gear oil and a "Superlight" gear oil:

http://www.redlineoil.com/products_gearlubricants.asp?productID=40&subCategoryID=15&categoryID=6

 

[Anime]

Actually, only the newer (1990's+) FWD cars use ATF or such fluids in their drivetrains. Plenty of earlier (1970-1980's) differentials/combo transaxles used 80W-90 gear oil.

Mostly it's been due to advances in lubrication and drivetrain engineering, so you can get a system that has less friction, generates less heat, and doesn't need a heavy lubricant, with the additional benefit of increased power/mileage.

That doesn't mean that a low viscosity ATF will now work as good as a high viscosity gear oil, though. Great improvements can be made by using a synthetic 75W-90 gear oil (Mobil 1, Castrol Syntec, etc.).

You might get some short-term benefits out of using ATF in a diffy of a performance vehicle made for gear oil, but you'd be changing it quite often and hoping it's lubrication properties were enough to slow the wear of the gears.

Gears are somewhat expensive and quite a PITA to change and adjust, so I'd say sticking with the suggested fluids is best unless you have the time and the dough to invest in case the gears wear out super quick, and anything else gets worn or damaged.