gear oil, ls modifiers and time

[surfride]

Given: Engine oils wax and thicken over time. What happens to gear oil over time? In my motorhome with a Dana S110, I will never hit the recommended 100k service interval. Jeep also states the gear oil in their manual transmission is good for the life of the vehicle. (seriously)

I have two questions:

Time:
How long can gear oil go between service via time, not miles?

Limited Slip Additives:
Every retail 75w90 out there I have found from Mobil 1, Valvoline, Lucas all contain this additive. Yet, none of my differentials require it the Dana 44 and S110 nor my 2500 GM; no clutches in any of them.
Does the additive in a heavy duty axle, the s110 or the 2500, suffer from this additive? Is the extra expense worth it for gear oil without any limited slip additive? In fact, Dana told me they will add a year to the warranty on their hd axles if you use their FE75w90 with no ls additive. The cost of Delvac 75w90 with no limited slip additive roughly doubles from Mobil 1 75w90. Is it worth it?

Thanks!

~David

 

[Ramblejam]

Originally Posted By: surfride
How long can gear oil go between service via time, not miles?


http://www2.dana.com/pdf/AXSM-0055.pdf (Page 45)

Originally Posted By: surfride
Does the additive in a heavy duty axle, the s110 or the 2500, suffer from this additive? Is the extra expense worth it for gear oil without any limited slip additive?


Neither will suffer, but the extra expense is a subjective decision if there's a warranty extension to consider.

 

[NMBurb02]

Originally Posted By: surfride
In fact, Dana told me they will add a year to the warranty on their hd axles if you use their FE75w90 with no ls additive.

I'm sure that has more to do with them selling more of their gear oil than non-LS gear oils being superior to those with LS additives. If LS was the real issue, the warranty would be extended for the use of any non-LS gear oil.

 

[UNC017]

LS additives aren't like viscosity modifiers. They're friction modifiers and therefore much more like anti-wear additives. They don't detract from the primary job of the oil, which is to lubricate gears. They just allow it to work better with limited slip clutches by preventing "chatter" or "shudder" from a fluid with a static friction coefficient that is significantly different from its dynamic friction coiefficient. Very, very similar to friction-modified ATF, like Mopar ATF+4 and others.

 

[Whitewolf]

If you don't need LS additive it's best not to use it. LS additives have side effects that are detrimental to some areas of performance, such as oxidative stability. In a plate type limited slip differential they are something of a necessary evil since they are needed in order to provide the appropriate friction characteristics. There are non-LS 75W-90 gear oils out there, if you want a list go to the gmpowertrain site and look for the DEXRON approved ones. (gmpowertrain,com).

 

[CT8]

I would change the oil.