Correct lube for Detroit Tru-Trac

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The instruction sheet said to use only conventional lube, not synthetic. The guy I talked to at Eaton said synthetic is "too slippery" to use in this limited-slip differential. Several YouTube vids said they are using synthetic lube with no issues. I have about 1000 miles on my Tru-Trac with synthetic lube.
Anyone here actually know the truth on the Tru-Trac??
 
I think what they are talking about is the limited slip additive in pretty much all synth lubes. Problem is, its getting to where its being put in conventional lubricants as well. I think the only way to avoid it now is to go to some specialty manufacturer or a heavy duty lube like Mobil Delvac 75W90
 
Originally Posted By: c502cid
Don't know why you can't use synthetic. There are no clutches in a True Trac.

Like he said, Eaton says no synthetic to be used, but will give no info on what is causing an issue besides "too slippery". Likely because it would single out one or a couple manufacturers and they can't legally do that. Its very frustrating. Theres a lot of theorizing on the intertubes and the limited slip additive angle is what I percieve to be the most likely, given their "too slippery" statement. It has no clutches, so obviously it doesnt need the additive, but its being added to almost all gear lubes.
 
Per the TrueTrac Operation Manual......
"High quality mineral gear lubes are required for use in Detroit Truetrac differentials. Regardless of the lube
type, alwys 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."
 
They've updated it then, and I was right on with the limited slip additive.
A few years ago the language was much more firm for "No synthetic."
I guess they've realized pretty much everything is using it now and had to lighten up.
code5, what viscosity does your vehicle call for? Maybe we can find a synth oil with no LS additive.
 
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I have a TrueTrac in my daily driver. I'm using Conventional lube based on Eaton's recommendations. However if I were to use a synthetic it'd likely be Redline 75w90 NS which is made without any limited slip friction modifiers.

I'm so pleased with how well my TrueTrac works with a conventional lube I'm unlikely to switch to a synthetic. I just change the lube more frequently. Which is easy since my differential has a drain and fill plug.
 
Think we had been through this before and an example was using Delvac 1 instead of Mobil 1 with LSD additives …

The axle builders & OEM truck company are also getting a “vote” in the process too ~ considering the multifaceted job the oil has to do
 
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The tru-trac provides the limited slip function using the friction created by driving the helicals and side gears into the case body. Using a "slippery" lube will result in the unit not locking up to the extent it would with a less slippery lube. Why not use what Eaton recommends?
 
Originally Posted By: lbhsbz
The tru-trac provides the limited slip function using the friction created by driving the helicals and side gears into the case body. Using a "slippery" lube will result in the unit not locking up to the extent it would with a less slippery lube. Why not use what Eaton recommends?

Because I don't buy into the theory that synthetic gear lube is "more slippery" than conventional lube. I DO know that it has other properties that make it more desirable than conventional lubes, and want to take advantage of that. AND because my vehicle's manufacturer calls for 75W90 synthetic gear lube..... that's what I put in (Valvoline SynPower, "for limited slip and conventional differentials".

Thank you, each and every one, for your insights and opinions so far. I'd like to hear from more of you guys who have some experience with this differential and its lubricant requirements.
 
Thanks, Duck. I just finished reading both threads in their entirety and came to the same conclusion that this thread led me to: Using synthetic gear lube will probably hurt neither the longevity nor the functionality of the Tru-Trac. Using synthetic or conventional oils with a friction modifier will not hurt the longevity of the Tru-Trac, but might affect its functioning to some unknown/unpredictable degree.
 
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Originally Posted By: code5coupe
Thanks, Duck. I just finished reading both threads in their entirety and came to the same conclusion that this thread led me to: Using synthetic gear lube will probably hurt neither the longevity nor the functionality of the Tru-Trac. Using synthetic or conventional oils with a friction modifier will not hurt the longevity of the Tru-Trac, but might affect its functioning to some unknown/unpredictable degree.


You got it!!!

I have a Eaton TrueTrac in the Dana 60 in my Camaro, I ran Valvoline 80w90 GL5 to break in the gears for 250 miles then switched to Redline 70w90NS because it was the ONLY synthetic GL5 gear lube I could find local (Summit Racing) without LS additive.
 
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Originally Posted By: code5coupe
Thanks, Duck. I just finished reading both threads in their entirety and came to the same conclusion that this thread led me to: Using synthetic gear lube will probably hurt neither the longevity nor the functionality of the Tru-Trac. Using synthetic or conventional oils with a friction modifier will not hurt the longevity of the Tru-Trac, but might affect its functioning to some unknown/unpredictable degree.


I agree with that assessment. I was thinking I had seen seen something that supported that conclusion from Eaton, I think the below video was what I was thinking of - skip to about 4:54 where he talks about lubricant.



OH, and you’re welcome of course.
smile.gif
 
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I've seen that vid several times. The part that plagues me is where he says "you do not need to use the friction modifier that is required in other types of limited slip differentials". I interpret this to mean you could use it, but it's not necessary. I wish he'd have said either "you can use it, but it's not necessary" or said "do NOT use a friction modifier". As it is, he's open to interpretation.
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Originally Posted By: code5coupe
I've seen that vid several times. The part that plagues me is where he says "you do not need to use the friction modifier that is required in other types of limited slip differentials". I interpret this to mean you could use it, but it's not necessary. I wish he'd have said either "you can use it, but it's not necessary" or said "do NOT use a friction modifier". As it is, he's open to interpretation.
mad.gif



He also said "a word of CAUTION" immediately before making that statement. As to emphasize what I interpret from their literature as not required and specifically not desired. I don't think that there is anything that's open to interpretation with regards to the desire for no friction modifier per the Eaton instructions.
 
That was my point...friction modifiers are generally desirable in diffs that use clutches, not this type of diff. They work correctly with the specified oil.
 
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