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Red2019

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Purchased transfer case oil from mopar and was wondering if I need to add anything to it.
Friction modifier?
 

c3k

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Purchased transfer case oil from mopar and was wondering if I need to add anything to it.
Friction modifier?

(Explanation not for you, but in case others are reading and wondering. And, I bolded part of your question.)

The transfer case is right behind the transmission. It takes the output and directs it, TRANSFERS it, to either just the rear drive shaft or the rear AND front drive shafts if four-wheel drive is called for. I have not heard of any need for any additives other than the appropriate oil.

The differentials (the pumpkin) on the front and rear axles exist to allow the wheels to rotate at different speeds when the vehicle is in a turn. The front differential is an open differential and will always send power to the wheel that resists less. (The truck uses its brakes to mimic a locking/limited slip differential on the front axle. This operation is hidden from the driver.)

The rear differential can be a Limited Slip version or an Electronically Locked version. The Limited Slip differential uses clutch packs inside the "pumpkin" to lock the axle halves together when the speed of the two halves exceeds a parameter. (This is purely mechanical.) For example, if the left rear is on ice, with an open diff, that wheel will get all the power and spin faster and faster while the right wheel, on dry pavement, will be stationary. The truck would be stuck. A Limited Slip will start to route power to the right wheel at certain point, allowing the truck to move forward off the ice patch. (The gears in the differential try to drive the axles apart. That property, with some springs and clutches, are what is used to lock the axles.)

The clutch packs in a Limited Slip differential needs friction modifier to make the oil "slippery". Otherwise the clutches will be too grabby and cause the axles to lock together when they shouldn't. The most common symptom of this is wheel chattering in a turn. (The outside tire moves a greater distance than the inside tire, but both rotate the same. Rubber skips and hops over pavement to keep up.)

The Electronically Locked rear diff uses an electric actuator to physically lock the two axle halves. There are no clutches. (Limited Slip is much better for normal driving. E-locker is probably better for off-road use in muddy/slippery conditions. Exceptions and opinions may vary. ;) )

So, if you're adding oil to a LIMITED SLIP REAR DIFFERENTIAL, yes, you'll need to add friction modifier if the oil does not have it already included. Read the label...or ask the dealer's service department if that's where you bought it.
 

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