Choosing diff lube with/without NS additive

[GeneralEclectic]

The equipment in question is an ordinary non-limited slip differential. Supposedly it has a 'lifetime' fill of lubricant which is BMW's version of 75W-90 gear oil, "XO" for anyone familiar with the product.

I want to change the lubricant because it has 50k on it and there's no such thing as "lifetime" fluids. I have some Mobil 1 75W-90 API GL-5 general purpose gear oil on hand. According to Mobil it's suitable for use in LS and non-LS applications. What I'm wondering about however, is whether the differential would be happier, and the frictional losses lower, with a lube that doesn't contain the LS additive. And if so, what would you guys think is a reasonable high-quality API-certified (no Redline) non-LS alternative?

 

[1040 WreckerMan]

Valvoline makes several "synthetic" gear lubes with varying degrees of synthetic base oil (depending on what you consider syn.) that are API certified. Most of the Valvoline products don't have the LS friction modifier in them and I have used 75w90 for a quite a while and been happy with it.

Mobil also makes a synthetic gear lube that does not contain the LS friction modifiers as well. I don't think you can go wrong with either choice, although what you have will work fine, IMO.

Specialty Formulations has some excellent gear lubes as does Schaeffer’s although they probably don' have all the certs you might see on the label of Mobil or Valvo. If money isn't a consideration I would certainly go with SF or Schaeffer.

 

[tdi-rick]

Hmm, I take it the factory fill is Castrol SAF-XO ??
This is a very good gear lube.
Anyway

quote:

---

What I'm wondering about however, is whether the differential would be happier, and the frictional losses lower, with a lube that doesn't contain the LS additive.

---

Ummm, LS additives make the oil, well slipperier to counteract clutch stick/slip or chatter and so it is my understanding, have a reduced co-efficient of friction. I'm sure your Bimmer will be quite happy with M1 75W-90.

 

[GeneralEclectic]

tdi-rick: Yup. XO, That's the stuff. So LS additives will tend to lower frictional losses in pinion-ring gear sets? Hmmmmm. Why then would anyone sell gear oil without the LS additives, theoretically? I'm not arguing with you, 'cos I have no clue about it. My assumption was just that, as a consequence of thinking what the lube would probably have to do to keep the frictional parts of a LS diff quiet. But hey, I've been wrong a million times before, why stop now?

So unless anyone chimes in with a contravening opinion, the Mobil synthetic 75W-90 is going in sometime in the next couple of days.

Thanks to both of you for the information.

 

[MolaKule]

LS additives are friction "modifiers" to prevent or reduce chatter in LS diffys by tuning the dynamic friction coefficient.

They don't improve gas mileage, that is the job of an additive called a Friction Reducer.

Friction Modifiers and Friction Reducers are in a class of additives called, "Friction Enhancers."

Friction Modifiers for Differentials and Friction Modifiers for Manual Transmissions are two different compounds.

 

[MolaKule]

Let me give you a little inside info.

Most blenders use a low level of LS additive just in case it's needed for the guy who has an LS. (The LS stuff is simply an ester of a phosphorus salt).

The LS add won't hurt anything in a non-LS diffy.

 

[bruce381]

"Friction Modifiers and Friction Reducers are in a class of additives called, "Friction Enhancers"

Thats backwards both friction enhancers and friction reducers are in that additve class of
"friction Modifiers" since a " modifier" can increase or reduce friction.
bruce

 

[GeneralEclectic]

You guys are going to make my head explode.

I think, but am not entirely sure, that I'm still good to go with the M1 75W-90 Synthetic with LS additive in the non-LS differential.

OTOH, I may just go looking for some of that Valvoline that doesn't have it, and use the M1 in the lawn tractor.

On yet another hand, I may run by my BMW dealer and pick up a couple of liters of SAF-XO on Rick's good review of it and use the M1 in the tractor.

Maybe I'll just flip my lucky silver dollar to decide.

Thanks for all the opinions.

 

[MolaKule]

Main Class - Friction Enhancers, general term for all the subclasses.

Subclasses - Friction Modifiers and Friction Reducers.

Friction Modifiers usually denote a class of chemical compounds in which the static and/or dynamic friction coefficients are modifed to prevent shudder and chatter, and to correct the friction coefficient in synchromesh/sychronizer assemblies for proper engagement.

Friction Reducers reduce the hydrodynamic and light boundary lubricantion friction coefficient for more economical operation.

 

[bruce381]

Sorry I disagree with your definition

Look up any aditives suppliers product list and you will see

Categories of their products

Friction Modifiers
used to change friction properties.
(They are NOT just for reducing friction)

Under friction MODIFIERS is

Friction enhancers
Friction reducers

Their is NO defintion as to where they are used your disciprtion is yours alone not mine or any one else I know in the business.

bruce