8 replies to this topic

[Jim Venable]

Recently used my last quart of 75W90 High Performance Gear Oil that read High Performance on the front.

 

The back of the container reads API GL-5+ Hypoid Gear Oil. Highest performance in Limited-Slip and conventional differentials. 

 

On the front of the new containers it reads:

 

75W90 NS.  GL-5 high performance lubricant for manual transmissions and transaxles. No mention of diffs. On the back of the container there is a sentence that reads:

 

Does not contain additives for limited-slip differentials.

 

Is the new packaging the same product many have been using or should we now be using a different Redline product for diffs?

 

Much appreciated,

Jim Venable

[davew]

Red Line 75W90 Gear Oil - the preferred product in nearly all car and light truck differentials, both conventional and limited-slip. 75W90 is preferred for most racing applications. It contains friction modifier which is recommended for limited-slip units. 75W90 Gear Oil can be used in many transmissions and transaxles; however, other Red Line lubricants have better frictional properties for rapid synchronization. Exceeds API GL-5.

 

Red Line 75W90 NS - a GL-5 which does not contain the friction modifiers for limited-slip hypoid differentials. This makes the transmission synchronizers come to equal speeds more quickly, allowing faster shifting and much easier low-temperature shifting. Can also be used in racing limited-slip differentials where weak spring design causes too much wheel spin.

[Steve Scheifler]

One point of possible confusion is that "friction modifier" seems to have opposite meaning for trans vs diff. If you add friction modifier to your trans it *increases* friction of the syncros. This is a common temporary fix for "slow" syncros. Friction modifier for clutch type limited slip diffs *decreases* the friction and reduces the chatter that some LSDs exhibit, but lowers your breakaway torque.

Do you have a Torsen or a clutch type LSD (old MS Comp or new Cusco)?

[ChrisA]

Jim, the 75-90NS designated oil is not new, nor is it a replacement for the 75-90 with slip modifier. Both have been available for a long time.

[Jim Venable]

Steve: MS Comp Diff

 

Dave: I understand.

 

ChrisA: Most clear.

 

I've used the same counter person (first name basis) at Carquest, now Advance Auto Parts, not to be confused with Dave's most excellent Advanced Autosports for ten or so years. I tell him it's fluid order time and he places the order. Never a problem until now. The HP product shows in their system but delivers the NS product upon ordering. Ordered twice. Therefore the issue is in the system switch from Carquest to Advance or they choose not to carry it. Hence my confusion. They will try one more time.

 

Perhaps my initial question and the answers will be of benefit to others. 

 

Again, thank you everyone. You're the best. 

 

 

[Steve Scheifler]

Passing along advice from Mark Bennett, the required breakaway torque on our cars is quite low. If you have been running the regular 75W90 (without the NS) and eventually start getting too much wheel spin out of tight corners, you can transition to the NS variety for a bit more bite. To get the full effect it may require some flushing to clear all the regular stuff out of the clutches.

[FTodaro]

Passing along advice from Mark Bennett, the required breakaway torque on our cars is quite low. If you have been running the regular 75W90 (without the NS) and eventually start getting too much wheel spin out of tight corners, you can transition to the NS variety for a bit more bite. To get the full effect it may require some flushing to clear all the regular stuff out of the clutches.

I will add to that

 

You can flush them with some cheap ATF fill it up and run for a few min. with the wheels suspended.

 

Redline 75/90 NS is expensive, you can also use Mobil Delvac 75/90 full syn. same result, less money.

[Bench Racer]

Jim, you have a pm.

[SaulSpeedwell]

Oh boy ....

 

"Limited Slip Differential" additive is generally a friction reducer intended for clutch-type (prealoaded plate) differentials.  Its purpose is to reduce "chatter".

 

Torsens do not need, and do not benefit from, "Limited Slip Differential" additives. 

 

I have TONS and tons and tons of respect and admiration for the inventor of the Torsen, Vernon Gleasman (RIP ...http://members.rennl...s84gleason.html) from my own Cleveland OH.  I wish I had come up with it, believe me.  But - despite Internet claims that Torsens never "wear out" and that they can run "almost any fluid", this is simply not true re: the former, and especially not applicable re: the latter, for those trying to get a 16+ year old/ 100K+ mile old/14+ race season old Miata around Mid Ohio's Keyhole or over Road America's "shock absorber durability curbs" with minimal or zero wheelspin.

 

Many OEMs made sure to specify a fluid WITHOUT "LSD additive" for their Torsens and Torsen-like LSDs.   I have lost the knack for uploading images here easily, but I'll edit this post when I can find my favorite example of an OEM spec for a Torsen LSD ...

 

Update:

Note link below ... "do not use special LSD oil"

http://mkiv.com/spec...cf93/ncf158.jpg

 

Like your manual transmission's synchros, the Torsen NEEDS friction to do it's job.  The last thing you want is the "slipperiest" fluid on the planet.  What you want is a hypoid gear oil to keep the gears happy, a low viscocity oil so that you can make 0.3 HP more so that you can finish 7th instead of 8th at the Smitty McSmitterson Memorial Regional, and a friction coefficient that maximizes your Torque Bias Ratio (Torsen) or synchro effectiveness (manual trans).