Overdrive

some XK models have an overdrive.

In this page i will explain how overdrive works

First off all overdrive is a feature to reduce gasoline costs.

In every car you have an engine with gears that is connected to the drive shaft which makes the wheels turn.

When you turn the engine, the driveshaft turns.

But there is a problem, if you want to turn the driveshaft one turn youŕe engine has to turn 3 and 3/8.

This is in the first gear, when you change the gear to a higher gear the engine has to turn less to make one turn on the driveshaft. See table below/

In the last gear the driveshaft and engine turning on a ratio 1:1.

 

For every gear there is another ration of turning between the engine and drive shaft.

Gear
Engine (turns) /  overdrive
Driveshaft (turns)

first
3,375 / 2,980
1

second
1,982 / 1,750
1

third
1,367 / 1,210
1

fourth
1 / 1
1

 
 
 

So now lets go to the overdrive.

Overdrive makes the engine driveshaft ratio go to a situation where the engine turns 1 time and the driveshaft more than 1 time.

Once overdrive is active you lose torque so it doesn't give you extra speed.