A Closer Look at Gear Lube

AMSOIL Synthetic Sever Gear SAE 75W-90 Lubricant

Automakers continue building vehicles that produce substantially more horsepower, torque and towing capacity than their predecessors, yet differential gears and bearings remain largely unchanged. Increasingly, synthetic gear lubes are recommended to meet these higher demands.

Increased Wear Resistance

Ring gear and input pinion in differentialDifferential designs come with inherent suffering points, and it’s here synthetics prove their worth. In a traditional automotive differential, the pinion gear concentrates intense pressure on the ring gear. As all the gear teeth mesh, they slide against one another repeatedly, separated only by a microscopic film of lubricant. The constant stress the lubricant film bears can shear lesser gear lubes, causing permanent viscosity loss. Once sheared, the fluid film weakens, ruptures and allows metal-to-metal contact, eventually leading to gear and bearing failure. The situation is worse in commercial vehicles used for towing, hauling and other severe-service application.

Conventional lubes formulated with viscosity index (VI) improvers shear more readily under stress. AMSOIL synthetic gear lubes, however, maintain viscosity better than other conventional and synthetic gear lubes despite rigorous use. AMSOIL Severe Gear® Synthetic EP Gear Lubes contain extreme-pressure (EP) additives that form a durable iron-sulfide barrier on gear and bearing surfaces to guard against metal-to-metal contact in the harshest conditions.

AMSOIL Server Gear Cost ComparisonIncreased Operating Temperatures

Differentials have always run hot, but increases in power and torque coupled with reduced fluid volume only worsen the problem. Testing has shown applications simulating trailer towing at 55 mph at a 3.5 percent grade can experience differential temperatures as high as 370ºF. Those readings could be even higher using today’s more powerful vehicles.

Thermal Runaway

As temperatures in the differential climb, gear lubricants tend to lose viscosity, while extreme loads and pressures can break the lubricant film, causing increased metal-to-metal contact and heat. The increased friction and heat, in turn, cause the lubricant to further lose viscosity, which further increases friction and heat. Friction and heat continue to spiral upward, creating a vicious cycle known as thermal runaway that eventually leads to greatly increased wear and irreparable equipment damage.

Here again AMSOIL synthetic gear lubes outperform conventional gear lubes. Not only do they resist viscosity loss due to mechanical shear, they resist thinning at high temperatures better than conventional lubes. In addition, the deposits conventional gear lubes leave behind coat gears and bearings, inhibiting heat transfer and shortening their life spans. What’s more, the lubricant thickens, increasing internal drag and reducing fuel economy.

AMSOIL synthetic gear lubes, however, are engineered in a lab and contain only uniform molecules less prone to volatilizing at high temperatures. As a result, they not only resist thinning in heat to provide better cooling and protection, they stay fluid in cold weather to ensure immediate startup protection. Their uniform molecules also reduce friction, effectively reducing drag and maximizing fuel economy. The lower cost of AMSOIL synthetic gear lubes combined with their extended-drain capabilities and superior performance make them the ideal choice.

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