[sperry]

Originally Posted by MattR

So, to continue with our conversation last night...What are the preferred fluids for 5MT/ 6Mt Transmissions.

You guys recommended the Redline Shockproof 75w90NS...

Does this have any effect on the DCCD in the STi transmission? I've looked around and haven't been able to find any negative effects, so I'm assuming it will be okay.

Any input?

Also, do I need a new plug gasket to replace when I change my fluid, or is it reusable?

RedLine 75w90ns is *not* Shockproof!

Here's a summary of the Redline gear oils applicable for our Subarus:

Redline 75w90ns:

"This GL-5-type geal oil doesn't 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."

This is good for the tranny if you're concerned with staying with a GL-5 oil. Frankly, I think it's too slick for the synchros, and will cause the tranny to shift poorly unless you're willing to double-clutch and rev-match more often than not.

Redline 75w90:

"Our most popular gear oil, this is 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."

I use this in my rear-diff. But it's not for use in the gearbox, due to the poor synchro performance that would result.

Redline Lightweight Shockproof:

"A unique gear oil designed to lubricate racing transmissions and transaxles which see serious loads (not recommended for most syncro-type transmissions). It has excellent low-temperature flow which allows easier shifting when cold. May be used to obtain maximum power transfer in racing differentials which do not see high temperatures. Similar to a 75W140 gear oil, but with the lower internal friction of an SAE 30 motor oil.

Used in two-stroke and four-stroke motocross transmissions (often mixed in equal parts with SuperLight ShockProof™ Gear Oil).

Used in most road-racing differentials with moderate power and dogring racing transaxles."

This is what I'd recommend. I'm actually using a 50-50 mix of Lightweight and 75w90ns, but I've run the straight shockproof before and liked it better (better synchro grab).