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Hypoid Gear Oil: What It IS And When To Use It

How using the right hypoid gear oil can extend the life of your vehicle

Hypoid gears are commonly used in automotive and heavy duty truck rear differentials where high torque and load handling is needed. Because these gears work under high pressure, gear oils that have been specifically designed to withstand and protect against these extreme conditions are recommended to extend the life of the hypoid gearsets.

What is a hypoid gear?

Hypoid gearsets are a type of automotive gear design. When you picture a gear, you probably imagine two rotating toothed discs that mesh straight against each other. This type of gear design tends to be noiser and, in automotive applications, inefficient. The hypoid gear design was invented to reduce gear-meshing noise and to provide greater torque and pressure handling as well as provide more durability.

Hypoid gearsets are fairly similar to spiral bevel gear setup, with the difference that hypoid gears have an axis that is non-intersecting and not parallel. In other words, the axis of hypoid gears are offset from one another. The basic geometry of the hypoid gear is hyperbolic, rather than having the conical geometry of a spiral bevel gear – kind of like a cross between a bevel gear and a worm drive. Therefore, the hypoid pinion is larger in diameter than an equivalent bevel pinion. This introduces a high degree of sliding motion on the gear tooth face of the pinion of a hypoid gearset and also increases the consistency of gear teeth intermeshing.

When are hypoid gears used?

Hypoid gearboxes are found in most of today’s modern vehicles. They are commonly used in rear axle differentials, where they transmit power from the driveline to the axle shafts. They are a type of spiral bevel gear with a left-hand spiral angle on the pinion and a right-hand spiral angle on the crown. This lowers the driveshaft away from the bottom of the vehicle, lowering the vehicle’s center of gravity, and in some cases, reducing interference with the interior space of the vehicle.

What is hypoid gear oil?

All vehicles require gear oil to provide lubrication in transmissions and axle differentials. Unlike normal engine oil, gear oil viscosity is generally much higher to Help combat the chances of extreme conditions squeezing a thinner fluid out and allowing gears to grind each other down.

Hypoid gearsets, by design, are under higher pressure than other types of gearsets. A sliding action of the gear tooth face is also introduced in combination with the rotational motion with a hypoid gearset that is not present in many other gear set designs. This elevated pressure and sliding action can cause the gear lubricant to be squeezed out from between the meshing gear teeth, causing metal-on-metal grinding.

Hypoid gear oils have been specially formulated to help protect these special types of gear sets. Hypoid gear oils can have higher viscosities just like other gear oils, but hypoid gear oils contain special extreme pressure and anti-wear additives that increase its resistance to breakdown under the high temperatures and mechanical pressure produced by the sliding surfaces of a hypoid gearbox.

When to use hypoid gear oil

As with all engine fluids and oils, regularly maintaining and changing hypoid gear oil can extend the life of a vehicle and its performance. Well-lubricated gears have less probability of pitting, breaking, or grinding against each other under pressure. Regularly changing gear oil removes wear material and other potential contaminates such as dirt and water. Not changing the gear oil can lead to accelerated wear of the gear set due to debris and potential rust and corrosion from water and oxidation by-products.

  • Kendall® SHP Syngear FE
  • Our next-generation, synthetic, fuel-efficient (FE) API GL-5 automotive gear lubricant is designed for use in passenger car and truck axles with hypoid gear sets operating in extreme temperatures or under severe driving conditions. It has been specifically formulated to provide improved fuel economy compared to typical mineral SAE 80W-90 or synthetic SAE 75W-90 gear oils.
  • Kendall NS-MP Hypoid Gear Lubricant
  • Our multipurpose, API GL-5 automotive gear lubricant is specifically designed for use in passenger car and truck axles with hypoid gear sets. It also is recommended for use in some heavy-duty manual transmissions in trucks and buses.
  • Kendall Super Three Star Synthetic Gear Lubricant
  • Our synthetic, API GL-5 automotive gear lubricant is specially designed for long-drain service and extended warranty protection in passenger car and truck axles with hypoid gear sets.