Change Gear Lube After Break-In Period for Long Differential Life

by Kevin Dinwiddie
AMSOIL Drivetrain Specialist Kevin Dinwiddie is a veteran of 28 years in the oil industry and a Certified Lubrication Specialist (CLS) by the Society of Tribologists and Lubrication Engineers (STLE).
This article appeared in Professional Car Washing Magazine, March 2007

Few motorists realize that most differential wear occurs during the first 5,000 mile break-in period. Quick lubes can do customers a service, as well as increase profits, by encouraging them to change to high quality synthetic gear lube following the break-in period in order to reduce wear and extend differential life.

Motorists know when they’re supposed to change their motor oil. They have oil life monitors, oil change centers and television commercials all telling them when it’s time for an oil change. Differential oil changes, on the other hand, often get overlooked. Many people don’t even think of the differential when performing routine maintenance on their vehicles and don’t realize four-wheel drive trucks have two differentials and a transfer case that all require service. In fact, according to one quick lube company, only one to two percent of their customers purchase a differential gear lube change.

Most differential wear occurs during the break-in period. Because differentials are not equipped with filters, break-in metals are suspended in the oil, causing increased wear as the particles mesh between the gears. Hauling heavy loads and towing heavy trailers  causes additional stress to the differential during the break-in period and can lead to premature differential damage or failure. Changing the gear lube after the break-in period (about 3,000 to 5,000 miles) is a low-cost maintenance investment that provides a significant payoff, including greatly reduced wear, extended differential gear and bearing life and protection for expensive vehicle investments.

Auto manufacturers recognize the importance of draining abrasive break-in materials. As seen in Chart 1, some manufacturers recommend an initial drain interval of between 500 and 3,000 miles.

   Chart 1

Differential internal components consist of six gears (one pinion, one ring, two side and two spider gears), six bearings (two pinion, two carrier and two axle) and sometimes include a clutch setup for limited slip performance. All of these parts require high quality, clean gear oil in order to perform at an optimal level.

Most pickup trucks, SUVs and vans operate in severe service conditions, including towing, hauling, steep hill driving, commercial use, plowing, , off-road use, rapid acceleration, frequent stop-and-go operation and high ambient temperatures. These severe service operating conditions subject the differential to extreme pressures and operating temperatures.

New vehicles such as turbo diesel trucks and vehicles with V-10 engines boast more horsepower and torque than their predecessors, but differential designs have remained virtually unchanged. Differentials today are subjected to severe duty service and encounter more stress and heat than was seen only a few years ago. Modern gear oils are challenged with  providing adequate wear protection during severe service operating conditions, while also providing maximum fuel efficiency.

According to a 2005 SAE paper titled “Breaking the Viscosity Paradigm: Formulating Approaches for Optimizing Efficiency and Vehicle Life,” concurrent with this strong drive toward better fuel economy, consumers have been demanding increased performance, which has required axle lubricants with enhanced durability protection and lower operating temperatures. There has been a 34 percent  increase in engine horsepower over the last decade, while axle gear sizes have remained constant, sump capacities have been lowered, and drain intervals extended. In the light truck segment there has been a 93 percent  horsepower increase since 1981.

Further evidence of stress and increased temperatures during the differential break-in period is documented in a 2005 SAE paper titled “The Effect of Heavy Loads on Light Duty Vehicle Axle Operating Temperature.” A light duty GM truck towing 14,000 pounds was driven from Orange County, Calif. to the Nevada state line. The test was conducted with both a new axle and a broken-in axle. Over level ground towing, oil temperature was measured at 230 degrees F in the new axle and 203 degrees F in the broken-in axle. Oil temperature over the most grueling portion of the trip, during which a maximum 6 percent  grade was encountered, revealed the new axle was operating at 350 degrees F and the broken-in axle was operating at 300 degrees F. Laboratory dynamometer test results simulating a truck hauling a trailer provided similar results, with level ground towing temperatures recorded at 266 degrees F with the new axle and 194 degrees F with the broken-in axle and towing temperatures (at a 3.5 percent  grade) recorded at 370 degrees F with the new axle and 295 degrees F with the broken-in axle.

For optimum protection in today’s differentials operating in severe service environments high quality synthetic gear lubes are recommended. In some cases synthetic gears lubes are capable of  extended drain intervals of up to 50,000 miles in severe service and 100,000 miles in normal service, or longer where specified by the vehicle manufacturer. AMSOIL synthetic gear lubes, for example, are formulated with shear stable synthetic base stocks and an extra treatment of additives. Unlike conventional petroleum gear lubes their excellent thermal stability prevents thermal runaway, a phenomenon caused by a lubricant’s inability to control friction and increased heat under high stress conditions.

Premium synthetic gear lubes are available for a full range of applications, including turbo diesel pick-ups, SUVs, vans, delivery/utility vehicles, light, medium and heavy-duty trucks, buses, heavy equipment, 4x4s, tow trucks, race cars, tractors and motor homes.

Synthetic gear lubes save motorists money through extended drain intervals, and they are also cost effective as compared to petroleum gear lubes.

Most customers are unaware of the importance of changing the factory-fill gear oil within the first few thousand miles. Synthetic gear lubes are ideal for owners of new vehicles so provide your customers a valuable service and recommend differential oil changes.  Your customers will appreciate the service and you will increase sales.