I have always run 75w-90 Synthetic in my differential.

I was just thinking today, why not use ATF in the diff?? Less friction, better fuel economy (maybe?). It can obviously work in a tooth to tooth gear box, as it is used in many manual transmissions.

Coments?

 

that'sa good question, however i've always ran synthetic gear oil in manuals that called for ATF. i doubt it would work very well, but i'd be interesting to hear soemoens results.

 

I think I might try it in the rear end of a Ford F-250 here at work. (don't want to hurt the Chev's w/an expiriment!) The problem (with that test) is that the trucks here are all used in low speed/off road conditions, so heat will not be an issue.

Anyone else who knows about the properties of ATF Dexron III vs gear oil?

-Tom

 

not sure if atf would be "extreame preasure" or not. atf is 30w from what i understand, the synthetic gear oils don't look much differant than 30w motor oil. i think low speed application would be the way to start and work up from there. trouble is how many hours/miles you going ot run it before deciding it works, or not? i tihnk the way to do it would be having the oil tested. in a rear that would be little bit of a trick and at 20 dollars a test get expensive.

 

Hi Ede.

We get oil samples for free through our petroleum vendor, so trying it and doing oil samples is a great idea. I guess I'd want to test the oil in extended increments, starting at maybe 500 miles.

 

I've got a couple thoughts on this idea.

First, the bearing clearances in the rear are designed to run in gear oil. I suspect that changing to ATF would severly decrease the life of the bearings.

Second, the gears themselves are set up to run in gear oil. I cannot see how ATF would provide enough cushion between the gear teeth. I think the gears would eat themselves up fairly quickly.

Third, synthetic gear oil does appear thin, but you need to remember that synthetic fluids are engineered to provide only the best properties of a typical petroleum product, and none of the bad ones. Gear oil, like any unmodified petroleum based oil, has about a hundred different molecules in it. Some of them are useful, others aren't. Synthetic oil uses only the molecules that are beneficial and necessary to achieve the desired properties of the oil. Just because the pourability of the synthetic gear oil looks like ATF doesn't mean that the weight properties are anyhting like ATF. You really can't tell much about an oil just by looking at it.

Summing all this up, I wouldn't even consider this in a vehicle that I cared about. A ruined rear could cost you hundreds of dollars to repair or replace, so I just don't think it's worth it.

 

That's why I'm going to try it in the Ford F-250! LOL! I fuggin HATE that thing. We have put more front end parts and trans parts in that ONE vehicle, than in the 16 other Chevy's that we own! Whoa, sorry obout that little rant.

TKO, I hear your reasons, but they don't explain to me the dfference between a rear w/ATF (tooth to tooth contact, bearings) and and auto trans, OR one of many manual trans's that run ATF. Tooth to tooth, and bearings, same as a rear. Only diff I can figure is there is ~300 ft lbs going INTO a trans, and with that same engine, over ~900 ft lbs going into the rear, albeit at a lower speed.

I don't know, I think it is a worthy test, and oil samples will show me how much metal I'm getting off the teeth or bearings, telling me if I should switch back.

Also, I'm not comparing this to synthetic Gear oil. I just said that that is what I have historically used. If it is comperable to plain gear oil, then that is good enough for me for certain applications. (my car not necessarily being one of them).

 

Rear ends need an EP additive for their hypoid gearset design. The reason is because when rear end gears mesh while turning under load, they actually try to wipe the the lubricant off the tooth faces. While it is true that the teeth of trans gears do slide across the face of each other somewhat (bevel cut ones more so), it's not near the amount that a hypoid gearset in a rear end does, which is why transmissions don't require a lube with an EP additive.

 

Exactly. If you look at the way the tooth is cut on an ring and pinion vs a transmission it is totally different. Plus, the material is different too.

Hey, if you don't want your F250 how much do you want for it? I'm looking for a work truck...

 

Probably $2000.

I don't know why you'd want it. The thing totally sucks, IMO. But if you're interested, it's a:
* '94
* F-250 ("heavy" 250 -8600 lb GVRW/Dana 50 front end)
* 49,346 miles
* White
* 460 Gas
* Auto (trans is 6 months old)
* 4x4
* Short cab log bed, bed has beed tossed and replaced w/a steel diamond-plate flatbed w/headache rack
* new cheapo mud service tires
* New brakes
* new wiper motor
* new upper and lower ball joints, both sides
* new U joint throughout the entire front end.
* STRIPPED! (crank windows, manual locks, AM radio, etc.)
* Engine oil changed every 2000 Miles

I personally hate this truck, but if you want it, by all means, it's all yours to come and get. Right now it runs fine, and just passed safety. I't property of The Canyons Ski Resort, so you'd be buying it from them, but through me, as I'm the Vehicle Maintenance Manager. Let me know.

 

I was half kidding. Sounds like a nice truck to me, but I don't think it's worth the 4,000 mile trip to go get it!

 

10-4. I was wondering about your location! Thought possibly you had moved but not changed your sig or something. I would have to agree that the thing isn't worth the trip, unless you're coming out to ski! Later.

-Tom