Synthetic lube for the rear axle?

OilPatch197 · Sep 23, 2008

Because of their special molecular structure, synthetic lubricating oils based on poly-alphaolefins (a type of SHC) and polyglycols ensure that tooth-related friction is considerably lower than with mineral oils. It may be up to 30 percent lower than if a regular mineral gear oil with EP additives was used. Because the friction coefficient of synthetic oils is lower, tooth-related friction is reduced, thus increasing the gear’s efficiency.

The efficiency of gears with a high sliding percentage, worm and hypoid gears, for instance, may increase up to 15 percent if a synthetic oil is used instead of a mineral oil. Even in the case of spur, helical and bevel gears (which have a naturally high gear efficiency), it is possible to increase gear efficiency of up to one percent by using a synthetic gear oil. This may not seem like much at first, but it may result in considerable cost savings depending on the nominal output of the gear unit, especially in the case where several gears are deployed.

So should I go Synthetic, is the above statement true? I've seen additives that you use with conventional oil(I think one is made by lucas oil) Can someone give me the straight dope on additives and synthetic oils for the rear diff and manual transmissions.

engdept · Sep 23, 2008

synthetic gear oils are nice. They have a friction modifier if you have a limited slip.

Will · Sep 23, 2008

What's it for in the rear axle? The average rear axle can go for 60+ years without a fluid change or even checking the fluid. And that's a 60-year old formulation.

cr_the_machinist · Sep 23, 2008

I use the Lucas synthetic gear oil in my front and rear diffs. The stuff works great, it doesn't break down as fast as standard gear oil. I add the Lucas oil stabilizer to my engine oil. Best stuff for your truck in my opinion. 4 quarts of Castrol Syntech and a quart of Lucas. You there no noticeable difference but if it's going to help prolong the life of the components, why not use it? I don't think it comes down to a game of friction but more in the factors of how fast the lubricant breaks down. There's no real percentage you can say that its going to improve but Lucas is the sh%t!

engdept · Sep 23, 2008

synthetics handle the heat better than conventional gear oils.

I too use Lucas gear oil and oil stabilizer in the engine.

Wicked_Sludge · Sep 23, 2008

im not a big fan of synthetics in engines...but i really like them for gears (where you dont have to pay to change them regularly). i run synthetic in my transmission, transfer case, and both axles.

engdept · Sep 23, 2008

I hate synthetic in engines, but since you can't buy dino oil Motorcraft, I am stuck with synthetic blend. The Lucas oil stabilizer isn't a synthetic.

Will · Sep 23, 2008

If it makes you feel better, than do it. It makes me feel better when people buy Lucas Oil products. They can help buy Bob Sanders some new knees with the dough.

exbass94 · Sep 23, 2008

Why all the hate for synthetic in engines? I'm switching my truck to Mobil 1 0w-30 next change. I'm actually switching everything to synthetic one thing at a time.

Will · Sep 23, 2008

I don't hate it. I just don't understand the expense. Especially in such a low wear part as an axle.

Wicked_Sludge · Sep 23, 2008

my personal reasons dont have a whole lot of science backing them...just personal experience.

firstly, i started to notice a trend on vehicles with synthetic motor oil. everytime i dropped the oil on one, it came out caramel or even gold in color (read: clean), and the oil filter weighed a bazillion pounds. that tells me that synthetics dont suspend particals as well as dyno oil does, thus loading the filter full of crud.

secondly is the "horror" stories we've all hear about switching a high mileage engine to synthetic causing leaks and low oil pressure...ive never actually witnessed this, but you know how urban myths are.

but mostly, i just cant justify the expense. we have several regular customers with more than 200k, and even a few with over 300k miles on dyno oil and their engines still run fine. if you ask me, thats overhaul territory anyway. and its cheaper for me to change my dyno oil every 3k miles than it is for the synthetic guy to change his every 5 or 6k.

exbass94 · Sep 23, 2008

My post wasn't really directed towards you Will, it was more towards Wicked and engdept who said they like synthetic in the drivetrain yet they don't like it for the engine, which I don't understand.

EDIT: Looks like Wicked was typing his post the same time I was. I don't really believe the whole synthetic being bad for high-mileage engines. I wouldn't hesitate to use syn in my Explorer with 141k or my 1992 Honda with 130k. I do however use either conventional or syn-blend in those because they don't get driven much and I too can't justify the expense. I'm mostly switching to syn in the Ranger because of it's good cold flow properties for this winter. It also supposedly increases gas mileage (I know, I know

) I'm VEEEERRRRRY skeptical of this too, but eh, I'm switching to syn anyway so we'll see.

Oh yeah, and 5k oil change intervals are the new standard for CONVENTIONAL oils. Synthetics can go even longer.

Jaymz9350 · Sep 23, 2008

Wicked_Sludge said:
firstly, i started to notice a trend on vehicles with synthetic motor oil. everytime i dropped the oil on one, it came out caramel or even gold in color (read: clean), and the oil filter weighed a bazillion pounds. that tells me that synthetics dont suspend particals as well as dyno oil does, thus loading the filter full of crud.

I thought the point of an oil filter was to remove the crud from the oil. I'd rather have it in the filter than running through the engine.

Wicked_Sludge · Sep 23, 2008

no, the point of the filter is to remove larger, heavier particles. motor oil serves a lot more functions than just lubrication, one of those is to attract and suspend carbon and other engine gumming deposites...this is the whole reason motor oils contain detergents and why we change our oil at regular intervals.

besides that i run a bypass-equipped filter and if the filter becomes prematurely plugged, there is no filtration occuring at all. meaning ALL those contaminents are circulating through bearings and other tight tolerance areas...not just the microscopic chunks.

Shran · Sep 23, 2008

I just run whatever is cheap in my junk. Oil is oil. Any oil you buy has to meet industry standards.

My only requirement is that it comes in 5 quart containers so I can drain the old back into it.

Synthetic lube for the rear axle?

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