Transmission oil type for 5 speed with limited slip diff.

[818speed]

I am a little confused as to whether I should use 75W90 or 75W90 NS gear oil. All signs indicate I should use 75W90NS, but I have a front differential installed in my transmission. Would this mean I should use standard 75W90?

[Bicyclops]

Good question. I just got a tranny from ZF with a Cusco. Gotta make a decision on oil pretty soon myself.

Ed Holyoke

[Hobby Racer]

I assume you mean you have an LSD front differential as all transaxles have a front differential

If your LSD is a Torsen type i.e. stock or Quaife style that uses gears and not clutches use 75W90 NS. NS stands for No Slip.

If you have a clutch type like the Cusco you will need the normal 75W90 as it has friction modifiers to help the clutches.

[RPGs818SNA]

As a starting point, this is the tranny oil Subaru specifies for a 2006 Impreza 5 speed:
Description: Genuine Subaru Certified High Performance Gear Oil SAE 75W 90, 1 Quart Bottle. Quantity Required: 2.3. Part Number: SOA427V1700, Quantity 4, Price $9.70
I believe the equivalent is 75W90NS, and FFR specifies 3.5 quarts. The price was the dealer's internet price which was better than my local auto store.
I don't know how having a limited slip differential might change the oil requirements.

[818speed]

I do have a Torsen type LSD. Since the LSD has gears, instead of clutch plates, it sounds like friction additives aren’t needed. Thanks for confirming Hobby. The stock fluid has the additives, but all the NASIOC forums indicate 75w90ns is the best for the tranny and the addition of a Torsen type LSD doesn’t change that.

[Hobby Racer]

I had a Quaife TBD (same as the Torsen) and I used Redline 75W90NS and it worked great.

[Sgt.Gator]

I use Redline 75W90NS in my Subaru race cars. Do NOT use Redline Shockproof.
Motul also has a lot of supporters.