Need 75w140 diff oil - 02' superduty with truetrac

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I need to change my diff oil. I have about 40k miles on mobil 1. I want to change it out and I see that mobil 1 is $19.99 at Advance and Valvoline full synthetic is $12.99 at autozone. Even with Advance discount codes, I cannot get the price down to the valvoline price. How do these two gear oils compare? I don't come here too often, but I know you guys are the authority. Thanks.
 
M1 gear oil would be better. True track? Does the mfg recommend a non syn oil?
 
You bring up a good point. The manufacturer (Detroit or Eaton) did recommend using a non-syn. But, when I researched it a few years ago, I was told that the syn was every bit as good and better. I usually stick with what is recommended, but got so many folks on the truck sites that said go syn. What do you think? Should I just use regular 75w140 gear oil?
 
My first thought was that it requires syn lube. Don't know why MFGrs say not to use syn gear lubes. Stupid..... I had a cam I bought years a ago that said not to use syn oil......?

Amsoil chart says to use a syn lube.
This is for the 5.4 motor..... probably the same as the 7.3, and 6.8 motor? You can put in your engine if it's different. I would use a good syn gear lube and not look back.....

http://www.amsoil.com/mygarage/vehiclelookuppage.aspx?url2=2002+FORD TRUCKS+F250 HD PICKUP+L
 
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Valvoline makes good oil, I have been using the synthetic 75W140 in my rear dif for the past year and it's doing great
 
I would use a 75w-140 from a Brand of your choice. The Valvoline product will work fine if that is what you want to use.

From the manual:

Detroit Truetrac®
High quality mineral or synthetic gear lubes are
required for use in Detroit Truetrac differentials.
Regardless of the lube type, always use a GL5 rated
lube with the least amount of friction modifier. Mineral
lubes lacking friction modifiers (limited-slip additives)
were historically recommended for all Truetrac
applications because friction modifiers can slightly
reduce the bias ratio (limited-slip aggressiveness) of
Truetrac differentials. However, to address the
continually increasing power outputs of modern
powertrains, many vehicle manufacturers have
switched to synthetic lubricants as a counter measure
for increased axle temperatures and prolonged service
intervals. In general, consult the vehicle owner's
manual for the manufacturer's recommendations for
lubrication type, weight and fill volume. This will ensure
lube compatibility with the seal materials and bearings
used in the axle. Eaton Performance technical support
is available for any concerns in lube selection.
 
You can get a gasket for the differential cover that makes oil changing a snap.
 
Do you guys approve of the Valvoline? At $13 per qt and available right at my local autozone, this seems like a good deal. Why go with mobil 1 when it is 50% more? Thanks guys.
 
Eaton recommends a gear oil without limited slip (LS) additives, preferably a non-synthetic. Most off-the-shelf 75W90 synthetic gear oils now contain LS additives. There are some 80W90 gear oils readily available without LS additives. I haven't researched what 140W gear oils might be available without the LS additives.


In addition to the statements from Eaton in an earlier post in this thread, Eaton also has the following on their Website:

Detroit Truetrac
A quality petroleum (mineral) based oil is recommended. Synthetic oils and friction modifiers should not be used, as they will decrease overall performance.

Detroit Truetrac®
What kind of oil should I use? Can I use synthetic?
Do I need friction additive/modifier?
Truetrac units perform best when using GL5 mineral /
petroleum based gear oil. Synthetic lubes are
discouraged. Do NOT use friction modifier additives or
lubes formulated with friction modifiers. See the
“Lubrication” section of this product manual for further
details and specifications.



I've purchased semi-synthetic SuperTech 75W90 to put in my TrueTrac. I would have gone with a conventional 80W90, but was unwilling to give up cold temp performance.
 
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I did not know some of the 75/140 synthetics come with LS additives. Is that the case for Mobil 1 and Valvoline? Should I just run the 75/140 conventional? Thank you for your help. I only have to change this stuff about every 5 years, so I want to do this right. Thanks again.
 
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I believe both the Mobil1 and Valvoline synthetic gear oils contain limited slip additives. If the bottle says the gear oil is suitable for limited slip differentials as is (without any additional friction modifier) it likely has friction modifiers already included. If the bottle says the gear oil is suitable for use in limited slip differentials as a top-off oil, it probably contains no friction modifiers.

If you want a synthetic 75W140 with no friction modifiers, Redline offers their 75W140NS. Make sure you get the "NS" type. Their non "NS" 75W140 contains friction modifiers.

If you are considering a non-synthetic, take a look at house brand gear oils. Some of them like Costal at Auto Zone and SuperTech at Walmart do not contain the friction modifiers. However, most conventional 140 gear oils will be 85W140 as opposed to 75W140 so they won't perform as well at cold temps.
 
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Hmmm, OK. The original LS in the truck called for friction modifier and came with the Ford 75/140 . So, maybe Motorcraft is the way to go. I wonder what they want for their lube.
 
The Motorcraft 75W140 does not come with any LS additives, in every shop manual Ford says to add the modifier inly if the vehicle has a Limited Slip that requires it. The Torsen T-2 in my Mustang does not require the additive.
 
Using a syn isn't going to hurt the truetrac in terms of damage, but it will slightly degrade the torque bias performance, and since that is what you seek in a traction control diff, why use something that will reduce the effectiveness? The same applies for the FM additives; they don't "hurt" the equipment, but they alter the performance in a negative manner to some degree (would vary based upon the amount of FM, basestock, etc).


There are a LOT of lubes that meet the SAE J-2360 performance spec; both dinos and syns. Why not pick one from that list, which neither is syn nor has FMs?

current listing here:
http://p-r-i.org/other-programs/automotive-qpl/lubricant/
current list was just done early this month

It would behoove you to check the product sites for the most recent info because some of them have FM in them in the bottle, and you'd want to avoid that.

Obviously a syn will likely last longer in service, but the dino lubes on this list have passed the very same strict and stringent (Mil-spec equvilant) J-2360 tests as do the syns.



So, my recommendation is a conventional lube, in your desired vis range, that does not have FM, that meets your favorite brand flavor.
 
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