Replacement of Gear Lubes Can Prevent Expensive Driveline Problems
Many vehicle manufacturers do not publish a recommended service interval for manual transmissions, transaxles, transfer cases or differentials, but some do. Chrysler, for example, says the transmission and transfer case on 1999 Jeep Cherokees should be drained and refilled every 30,000 miles or 24 months. Other manufacturers, though, say only to inspect the fluid level periodically and add as needed to maintain the proper level.
The oil level inside a transmission or differential is critical for proper lubrication because there's no oil pump to route the oil where it's needed. The oil is churned by the whirling gears, which "splash lubricates" the moving parts.
If the fluid level gets too low because of a leak, therefore, the
bearings and gears won't get enough lubrication. The result can be
galling, seizure and total destruction of the unit. Oil is also
necessary to cool gears and bearings. The total oil capacity of most
manual transmissions, differentials and transfer cases isn't very
much (typically a couple of quarts or less), so it doesn't take much
fluid loss before parts start running dangerously hot.
Most conventional oils thicken as the temperature drops. This
increases friction, drag, fuel consumption and the effort
needed to shift gears. During subzero weather, a heavy gear oil
inside a manual transmission can make the shifter feel stiff and
clunky. The gears may even grind when changing gears until the
vehicle warms up. The cure here is to replace the conventional gear
oil with a synthetic gear oil.
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Last modified: January 21, 2011