|
The Importance of Early
Gear Lubricant Replacement for Long Differential Life
Unbeknownst to many motorists, most differential wear occurs during the
break-in period.
  Motorists
know when they’re supposed to change their motor oil. They have oil life
monitors, oil change centers and 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 cause additional stress to the
differential during the break-in period and can cause premature differential
damage or failure. Changing the gear lube after the break-in period (about
3,000 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.
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, racing, 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 faced with the challenge of providing
adequate wear protection during severe service operating conditions, while
also providing maximum fuel efficiency.
In fact,
according to a 2005 SAE paper entitled
Breaking
the Viscosity Paradigm: Formulating Approaches for Optimizing Efficiency and
Vehicle Life,
“Concurrent with the 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% 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% horsepower increase since 1981.”
Further
evidence of stress and increased temperatures during the differential
break-in period is documented in a 2005 SAE paper entitled
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, California 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% 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% grade) recorded at 370 degrees F with the new
axle and 295 degrees F with the broken-in axle.
AMSOIL
SEVERE GEAR™ 75W-90 and 75W-140 Synthetic Gear Lubes are formulated for
severe service applications, protecting differential gears for 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. Formulated with shear stable synthetic base stocks and an extra treatment of
additives, SEVERE GEAR™ Gear Lubes provide unsurpassed wear protection and
friction reduction, while 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.
AMSOIL
SEVERE GEAR™ Synthetic Gear Lubes are recommended for 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.
 AMSOIL
Synthetic Gear Lubes save motorists money through extended drain intervals,
and they also cost less per quart compared to many competing OEM gear lubes.
A test on
four separate vehicles further demonstrated the importance of changing the
factory-fill gear lube within the first few thousand miles. Oil analysis
results revealed most of the wear in vehicle one occurred within the first
6,869 miles. Despite higher mileages, vehicles two and three only showed
slightly higher iron wear than vehicle one. Vehicle four was the only
vehicle which had the factory-fill oil changed to AMSOIL synthetic gear
lube, and despite significantly higher mileage than the first three
vehicles, it showed a significantly lower level of wear.
 The chart
(right) and
photos below provide visual evidence of the wear materials present in the
differentials of each vehicle. The photos clearly show that the heaviest
amount of wear occurs early in the break-in period.
Wear is
significantly reduced when the gear lube is changed to AMSOIL synthetic gear
lube following the break-in period.
 |
