Rear gear oil for LSD

[Thefunk]

Amsoil SG 75W-110 is (or was?) very popular with the Evo 8/9/X crowds for the rear diff & xfer case. Those things take some serious launch abuse at the dragstrip though. A straight 90 weight gear oil was factory-fill (and what I always stuck with). Same goes for the S2k diff which was known to be made of glass (straight 90 factory-fill).

Since then, the SAE spec for 90 weight has changed so today's SAE 110 is more similar to the 90 of old.

So the weight of today's 90 is that of 110 of old? If you buy 7w90 it has the weight of 7w110?

 

[KrackaC8]

So the weight of today's 90 is that of 110 of old? If you buy 7w90 it has the weight of 7w110?

Reverse that, they thinned out the spec. A modern 75W-110 today is what a 75W-90 use to be.

The 75W-85 I run in my Jeeps (Redline and/or Amsoil) is basically a 70W-80 by historical standards.

 

[Thefunk]

Reverse that, they thinned out the spec. A modern 75W-110 today is what a 75W-90 use to be.

The 75W-85 I run in my Jeeps (Redline and/or Amsoil) is basically a 70W-80 by historical standards.

I'd make an assumption that the viscosity standards are strict for marketing. How are they getting away with selling 90 weight as 110?

 

[KrackaC8]

I'd make an assumption that the viscosity standards are strict for marketing. How are they getting away with selling 90 weight as 110?

SAE changed the specs to decrease viscosity and increase efficiency. No marketing, these are technical specifications. This impacted all gear oils regardless of brand. These specs are continually being revised as needed.

 

[FSUZ33]

For the handful of us that don't perv out over automotive lubricant specifications (no offense, you help others out, so You Do You Bru!) does the conventional vs synthetic note/spec in the manual for the LSD bear weight?

 

[KrackaC8]

For the handful of us that don't perv out over automotive lubricant specifications (no offense, you help others out, so You Do You Bru!) does the conventional vs synthetic note/spec in the manual for the LSD bear weight?

No offense taken! Both my wife & I are in the automotive fuels & lubricants industries. I've been a gear head since oiling my bike chain as a child.

They add that note to ensure the differential fluid has enough friction for the LSD clutches to function. This is why the quality synthetic gear lubes add a friction modifier. Win-win as you get the increased gear/bearing protection of a synthetic lube, but enough clutch disc friction for the LSD to function. The con? Higher costs...which mass production manufacturer bean counters actively avoid.

 

[FSUZ33]

I knew I could count on you

@KrackaC8 is to lubricants as Hank Hill is to propane and propane accessories

Tri Flow all day long for bike chains