Synthetic vs. Dino Gear Oil

Hi All-

I have been wondering about the merits and drawbacks of synthetic gear oil in the front and rear differentials. I changed both of them myself to Mobil1 75-140 synthetic last summer, but have since read that synthetic gear oil may not be as heavy and may not protect the gears as well? What are your thoughts on this?

Also, is there anything special that would be involved in switching back to dino gear oil, besides a can of brakeleen?

Running regular old Dino in mine and no problems at all.
Clings better

MadDog said:

Hi All-

I have been wondering about the merits and drawbacks of synthetic gear oil in the front and rear differentials. I changed both of them myself to Mobil1 75-140 synthetic last summer, but have since read that synthetic gear oil may not be as heavy and may not protect the gears as well? What are your thoughts on this?

Also, is there anything special that would be involved in switching back to dino gear oil, besides a can of brakeleen?

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The properties that make synthetic oils better in a forced oiled system like a engine or trans is not what you want in a splash oiled system that your diffs use.Synthetic gear oil does not transfer heat like dino gear oil can,hence the shorter OCI's for diffs using synthetic.Sure dino gear oil thicker,and will reduce mpg's by a very small amount,but it sticks to the gears and bearings much better providing better lubrication.Almost every aftermarket diff company only recommends dino gear oils for there diffs.

X2 as above.
I have talked to a main local 4x4 diff re builder, and his statement was...
Use regular gear oils like GL5 and your diffs will last without much wear...the same can not be said for those that use synthetics.
He also recommended LUCAS gear oils as really excellent quality that stick phenomenally.
http://www.lucasoil.com/products/display_products.sd?iid=43&catid=12&loc=show

I have built and rebuilt hundreds, if not thousands of diffs.....can always tell the ones that used synthetic. The synthetic have relatively low miles, hammered teeth, and general carnage. the dino diffs have very high mileage, well worn teeth, and just plain old worn parts as normal with 150-200 k miles.

A recent Hotshotter with a 2001 dodge 3500 (D80, 4.10, Detroit locker) just turned 650k miles with the original gears, pinion bearings, seals and hub bearings. The Detroit was installed with new carrier bearings at about 10k miles, so the carrier bearings have that many less miles than the rest of the components. The hub seals were replaced at around 50k miles, and the replacements have been leak-free. The gear oil of choice has been Coastal 85-140.

the diff has been showing signs that the tolerances are opening up a bit, so it iwll probably be due for a going through in the next 100k.

Thanks guys! I will probably switch back to Dino oil in the diffs this summer. Is there anything special switching back and forth between the two that should be done? I'll use a can or two of brakeleen, but just wondering if there is anything else I should do.

Thanks!

I will be changing my diff fluids soon and thought I had read on here to use atf+4 in the diffs. After reading this I was just wondering what you guys would recommend for gear oil. Looks like Lucas Oil is a good product. What weight should I be using?

the diffs need gear oil...ATF+4 is used in the transfer case.

Using ATF+4 in the diff will cause a failure in short order.

I know ATF+4 is used in t-case. Just mistakenly read the proper diff fluids. what weight would you guys recommend? Thanks in advance.

fishin'liberty said:

I know ATF+4 is used in t-case. Just mistakenly read the proper diff fluids. what weight would you guys recommend? Thanks in advance.

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80w-90 for normal driving,85w-140 for towing/offroad.

Switching from Synth to Dino gear oil...

MadDog said:

Thanks guys! I will probably switch back to Dino oil in the diffs this summer. Is there anything special switching back and forth between the two that should be done? I'll use a can or two of brakeleen, but just wondering if there is anything else I should do.

Thanks!

Click to expand...

Looks like nothing special needs to be done when switching from synthetics to dino gear. Thanks to LibertyTC's link to Lucas Oil I grabbed the following Lucas Oil-provided description of their 85W-140 gear oil:

Features & Benefits
Lucas SAE 85W-140 Gear Oil is a technical blend of oils and additives designed to give longer oil life and longer component life with less power draw. It is formulated with special anti-wear agents and anti-seize agents not found in common gear oils. It contains special lubricity agents for less wear, less heat, less power usage and longer bearing life.

• Ideal for older gear boxes
• Slows or stops all oil leaks and cushion gears to reduce lash in worn gear sets
• Guarantees a cool, quiet performance with minimal drag
• Resists breakdown from contact with water
• Blends with other gear oils, even synthetics

Bob

Straight out of the 2006 FSM:

04Liberty, You know, Mopar fluids are notoriously CHEAP that's why they're reccomended...

Mopar 75W/140 fluid here is as expensive as gold and I'm not sure it's worth while. Just IMHO.

I either use Shell Spirax or a cheap though not so bad local brand ( Venoco ).

I am running 75/140 synthetic front and rear diffs.

I have a bunch of fluid changes due. Got pleanty of ATF+4 for the t-case and just picked up some HOAT at NAPA. I will be picking up the diff fluids this week also. Going back to dino. Not sure what brand yet but I am going to stick with 75/140 as I tow and fool around off-road some and I only have 1 gear lube pump for diff fluids.

Dave

Dave said:

I am running 75/140 synthetic front and rear diffs.

I have a bunch of fluid changes due. Got pleanty of ATF+4 for the t-case and just picked up some HOAT at NAPA. I will be picking up the diff fluids this week also. Going back to dino. Not sure what brand yet but I am going to stick with 75/140 as I tow and fool around off-road some and I only have 1 gear lube pump for diff fluids.

Dave

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You'll be hunting for 85w-140 dino gear oil.

tjkj2002 said:

You'll be hunting for 85w-140 dino gear oil.

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Ok then, 85/140 dino it is.

Dave

diyman said:

04Liberty, You know, Mopar fluids are notoriously CHEAP that's why they're reccomended...

Mopar 75W/140 fluid here is as expensive as gold and I'm not sure it's worth while. Just IMHO.

I either use Shell Spirax or a cheap though not so bad local brand ( Venoco ).

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Which is why I don't use them, I posted that more for oil weights and where it listed synthetic. Other than actual parts, I don't buy chemicals from Mopar (or I wouldn't have any $$ for parts!).

fishin'liberty said:

I will be changing my diff fluids soon and thought I had read on here to use atf+4 in the diffs. After reading this I was just wondering what you guys would recommend for gear oil. Looks like Lucas Oil is a good product. What weight should I be using?

Click to expand...

i hope you didnt put atf+4 in your diffs....tell me you didnt.

flair1111 said:

i hope you didnt put atf+4 in your diffs....tell me you didnt.

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Sounds sticky.