Overdrive Unit
An overdrive is an extra gear unit behind the gearbox that lowers engine speed at cruising speed, common on older cars.
What is Overdrive Unit?
It is often switched electrically from a lever or switch. It may work on top gear or several gears. It reduces noise and fuel use on long trips. Engaging and disengaging smoothly needs a brief lift of the throttle on many systems.
How it works
A planetary gear set gives an output faster than the input when engaged.
Why it matters for your car
Check oil level, as overdrive units are sensitive to low or wrong oil. Faults are often electrical, such as a solenoid or switch.
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