Ok so i got the car yesterday and am slowly giving it a solid tune-up. So far I've done engine oil, ATF + spin filter, air filter, sparkers, new coolant and front gear lube oil.

 

So now the problem: I have a rear VLSD but im afraid to change the oil. It's a visco type deal but regular old 75w-90 doesn't gel with temp like the book theory eludes to. There must be a special visco additive but the dealer thinks I'm nuts.

 

What gives.

 

2007 Forrester LL Bean 38,000 miles

Theres a few different brands out there that have LSD rear diff fluid.

The dealer should have this fluid also.

Motul 90PA

Redline

And some others.

Isn't the viscous LSD fluid separate from the gear oil in those? And it doesn't need changing? The clutch type needs the fluid with the additive. I could be off, but that is what I remember.

That's how I remember it as well - the VLSD's have a sealed viscous coupler just like the EJ center diff component on the 5 speed's..... they take plain old gear oil.

 

GD

Diffs with sealed VLSD units (and Torsen diffs, if anyone is wondering) don't require friction modifying additives.

After further research I see I was wrong and the others are correct.

The VLSD are a sealed unit. This is a longish read, but very informative.

 

http://forums.nasioc.com/forums/showthread.php?t=1442522

http://forums.nasioc.com/forums/showthread.php?p=15812529

 

Viscous: Used as the center and rear differentials in the WRX/RS (08+ WRX has an open rear diff). Varies power applied between two axles via fluid dynamics and discs. This type of unit is filled with a silicone based fluid that becomes thicker as the difference in input shaft and output shaft speed increases, thereby increasing the viscosity of the fluid and the grip between the input and output discs, which do not actually touch each other.

Ahhhhhhh...

 

Thanks. It's a sealed unit. I feel much better now.