Part One: Perhaps the most common question we hear, here at Torsen® Intergalactic Central, is “what oil do you recommend?” It seems simple enough, right? Well, not so fast there, pal – it’s not a black and white matter. You may have heard that oil is your engine’s life blood; for all the geared systems within an automobile that is also true. Typically, the differential shares its lubricant with other components. In a rear axle, that includes the ring & pinion set as well as the axle bearings.  For a front wheel drive transaxle, however, that also includes the entire transmission system.  This entails the gears, the bearings, the syncros, everything.  The catch is that a limited slip differential – like Torsen – works by creating friction. On purpose. So, you have to balance proper lubrication with allowing the differential to do its job. That means a trade-off.

In reality, a limited slip differential is the only (oil-lubricated) component within a vehicle that intentionally produces friction. Friction within the differential is what gives it resistance to wheel slip.  And, as previously noted, the ability to transfer torque in an advantageous way. So, choosing a type of oil that has minimal reduction of friction is the obvious answer, right? Yet, the differential is spinning on bearings within the axle.  That whole system uses the same oil, including the final drive gearing.  It all needs proper lubrication to survive. Gear life directly depends on proper lubrication.  Lubrication also has a direct impact on other factors, like fuel economy. This is why lube choice is tricky – and why vehicle manufacturers spend a lot time testing, both for performance and for durability.

In truth, a Torsen differential typically isn’t that fussy about which lubricant you choose – within reason. A Type-2 or T-2R model will operate in really any common lubricant, ranging from ATF to heavy weight gear oil. On the other hand, if you happen to be using a Type-1 differential, you need to a little more choosy.  The crossed-axis gear mesh of Invex™ gearing requires the use of oil with high-pressure additives. This means they need gear oil with a GL-5 rating. But even that isn’t too difficult.  Hypoid ring & pinion gears have the same need, so almost all normal axle lubricants are up to the challenge. But be sure to look for the rating on the bottle anyway.

Because the ring & pinion final drive gearing are constantly running, they are a lot fussier regarding proper lubrication. So, your best bet is to seek out the recommendation of the ring & pinion manufacturer. If your car came with a Torsen from the factory, then you can find that information in your owner’s manual. Or, if you’ve installed a different gear set or changed ratios, go back to the supplier or manufacturer of the gearing you used. Most are very specific about what fluids should be used during break-in and normal operation of their gears. But either way, if the lube is suitable for your final drive gearing, the Torsen will be happy as well.