OK to run gear oil for LS in nonLS Diff?

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Yep, it's fine. Been running Mobil 1 75w-140 LS in my WRX's rear diff (which is a sealed viscous LSD) for around 15,000 miles now.
 
Consider that the LS is great for gears and bearings in the limited slip assembly.
So why not be perfectly OK without the additional clutch pack and the same gears?
 
Originally Posted By: Back40
The only 75w90 full syn gear oil I can find is for Limited Slip diffs. Is it ok to run this in a non LS diff?


Not a good thing to do.

Fms are not good for oxidation so you don't want them unless they are really needed.
 
Originally Posted By: Whitewolf
Originally Posted By: Back40
The only 75w90 full syn gear oil I can find is for Limited Slip diffs. Is it ok to run this in a non LS diff?


Not a good thing to do.

Fms are not good for oxidation so you don't want them unless they are really needed.


True, but the oil companies add so little (usually not even enough to stop a clutch pack type limited slip diff's chatter at all!), and such a weak form of it, that it will probably cause little to no extra oxidation.
(Especially as compared to adding 4+ ounces extra of a very strong friction modifier such as Ford/Motorcraft XL-3
wink.gif
).
 
It's fine. The LS additives in regular gear oils will do no harm in a non-LS differential. Off-the-shelf Mobil 1 75w90 LS is what I use in the 01M VW four speed junkbox differential and it works great. The rest of the transmission... it needs all the help it can get.
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Originally Posted By: scurvy
It's fine. The LS additives in regular gear oils will do no harm in a non-LS differential. Off-the-shelf Mobil 1 75w90 LS is what I use in the 01M VW four speed junkbox differential and it works great. The rest of the transmission... it needs all the help it can get.
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First of all, it is well proven and well documented that the addition of LS additives into GOs can result in a 3-400% at least degredation in oxidation performance. If you want to verify this, you can do a search on SAE papers that support this statement.

Secondly, if (as somone said earlier) you want to talk in terms of ounces, then you need to be in touch with the fact that the ounce includes the FM content of the carrier fluid ... so talking in terms of ounces of FM is rubbish because you don't know what the FM content was, and you don't know what the carrier fluid is.

I hope that helps.
 
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Whitewolf knows what he's talking about.

FMs are not a good thing unless you need them to avoid chatter... add only as much as you need to eliminate chatter.
 
I'm going to add this to the list of things that shouldnt be done, that I do anyway and have for a combined hundreds of thousands of miles and have never had a problem as a result of doing it.
 
Quint- What a silly thing to say.

The difference in oil life (oxidation) between a moderate/correct load of FM is fairly small in the average, easily used car/truck, especially considering normal maintenance usually has the oil dumped before it fully breaks down. Oxidation will occur more rapidly with heavy use, accelerated by the FM, so if you were a guy that tows a lot and gets the oil hot, you'd have less of an oil life cushion. There are stats on how much the oxidation rate increases with FMs but in many cases, they might not be significant.

The problems come when people add too much FM. It happens often and I have been told that at least some of the unexplained oil or axle failures can be attributed to it. I have watched guys add way more than was called for (perhaps under the premise that if "X" amount is good, "X x 2" is better). I wish I could have followed up on those guys.

I won't speak for Whitewolf but my main motivation in pressing this point is to make sure the concept and potential are understood so that people will just exercise a little care in;

a) knowing that your oil will break down faster long term or in hard use, and;
b) to add only as much FM as specified or as little as necessary.

Just trying to help, that's all.
 
Next change I am going to try not adding ANY extra FM fluid.

I want to see if the amount/type which either Red Line or Amsoil add to their gear oils is enough for my Eaton cf clutch pack posi to function with max lockup, and little to no noise/chatter.
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dailydriver- In the cases I've looked into, the synthetic oil blender does not add ANY FMs. The base oil, and its normal additive package, has the right friction characteristics without any special additives. IIRC, the two you mentioned were on that list.
 
Jim,

What am I being silly about? Back40 asked if it was ok to use an off the shelf gear oil that already comes with LSD additive in it, in a regular differential.

I get that the additives affect oxidation. I get that adding way too much additive to a gear oil is a bad thing. I not advocating doing that (no one else did either).

Thats not what the original question was anyway, so I'm not even sure why that was even brought up. It seems to me questions are being answered, that arent being asked.

He wants to use a synthetic fluid with LSD additive already in it, in a regular differential. Is it going to hurt anything? As you said, oxidation rate increases with FMs but in many cases, they might not be significant. I agree. As someone else said, many of these LSD-ready gear oils dont even have enough FM to do what they are supposed to do to begin with. There isnt enough in there to even worry about it. Hence my previous answer.

Thats my answer, I'm sticking to it.
 
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I have watched guys add way more than was called for (perhaps under the premise that if "X" amount is good, "X x 2" is better).
If it is good to put a little bit on, then it's better to put more on. That's the moron theory.

What top quality GL-5 gear oils do not come with limited slip capability these days? All the labels I see say that they are suitable for LS differentials, which means they have some friction modifier added.
 
Hi,

You are not correct. There still are fluids that require the addition of FM for plate diff applications. The newer fluids do not because the FM is already included e.g. the Corvette axle fluid.

That same fluid is also manufactured without FM for open diffs where FM is not only not necessary but can result in significantly reduced oxidation performance.

What I'm telling you is not an opinion it's a fact that is well known in the oil and additive industry for many years and has been documented and published.
 
So is it also a fact that is well known in the oil and additive industry for many years that people using these horrible fluids in their open differentials, are experiencing untimely failures of same?

Because its also a fact that I have been doing this for literally as long as I can remember without a single differential failure.

Not trying to be saracastic (well, maybe a little) but I am coming up on the 1/3 of a million mile mark on one of them, and I would like to know when its going finally give up as a result of me having done this.
 
Originally Posted By: quint
So is it also a fact that is well known in the oil and additive industry for many years that people using these horrible fluids in their open differentials, are experiencing untimely failures of same?

Because its also a fact that I have been doing this for literally as long as I can remember without a single differential failure.

Not trying to be saracastic (well, maybe a little) but I am coming up on the 1/3 of a million mile mark on one of them, and I would like to know when its going finally give up as a result of me having done this.


You still don't seem to be grasping the point and appearing to be obstinate just for obstinacy sake. Where did anyone say the FMs were "horrible" and causing "untimely failures?"

The info was simply presented as an FYI. Your open diff will not die immediately by adding LSD FMs to the gear oil, or having those FMs in it, but oil life will be shorter. Better if you don't use it but it's not immediately harmful if you do.

Second, are you an automotive engineer? Whitewolf is. He works in the drivetrain division of a major auto manufacturer and has to deal with lubricant qualifications/recommendations... probably on a daily basis. He would know because it's his business to know so that he can prescribe the right lubricants.

Me, I'm just a oil-geek schub who reads a lot, so feel free to discount anything I say.

Finally, you haven't put much skin in this game, except to relate some vague anecdotal observations. A few more details from you would help us to understand your POV, to whit:

Are you saying you went 333,000 miles on one fill of oil that had FMs in it and you tested the oil and it was fine? That would be very interesting info.

Or, are you saying you did routine maintenance and never had a failure over 333,000 miles. If so, what were your OCIs, what oil was used and what vehicle is it?
 
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