What is overdrive?

Overdrive is a special gear in vehicles and its overall function is to reduce the rpm on a car’s engine and save you fuel. In this overdrive gear, it gets the engine to perform optimally and provide fuel efficiency at higher speeds. Unlike low gears, overdrive has a gear ratio of less than 1.0:1. This means that when in overdrive your car can drive at faster speeds but at a low RPM. The wheels of the car will rotate faster with each engine rotation, allowing the speeds to remain high and the engine RPM to stay low. 


Where is overdrive located?

The overdrive button (O/D) is normally located on the gear shifter. It is usually on the left side of the shifter, below the button used to shift the gears. On newer vehicles, it is an electronic computer that will automatically adjust when it needs to be turned on. 


How does overdrive work?

The overdrive system is an electrically operated gear train that is bolted behind the transmission unit. To incorporate it into the car it can couple the input drive shaft directly to the output shaft or, to increase the output speed so that it will turn quicker than the input shaft. This means the output shaft could be overdriven compared to the input shaft. 

In newer transmissions, the overdrive speeds are a result of different combinations of gear sets. These gears are integrated into the vehicle’s transmission. 


When to use overdrive?

It is best to use overdrive while driving at higher speeds. Overdrive should only really be used when you are traveling in higher gears. The ideal driving situation to use overdrive would be on a long drive while driving at 100kph.


When not to use overdrive 

Overdrive shouldn’t be used while driving in low gears. Overdrive at a low speed will not allow you to accelerate as you normally do. So it is best to turn your overdrive off when your car is climbing a hill and going down steep hills. You should also not use your overdrive while carrying or towing a heavy load. In these situations, it is beneficial to be able to rev the engine a bit more. 


Overdrive Fuel Consumption

When driving at fast speeds in high gears it is best to have your overdrive on as is better for fuel economy. Overdrive will save you money because it makes your car drive more efficiently and keeps your engine running at its optimum capacity. Having your overdrive off can increase your fuel consumption. 


Overdrive issues

If you’re having overdrive issues it is best to get it inspected by a qualified mechanic. Symptoms of a failing overdrive can be the transmission revs higher before it changes gear when the overdrive is turned on. The vehicle’s transmission engaging into overdrive is delayed and sometimes won’t go to the top gear. Lastly, the brakes are sometimes harder than normal when coasting, and that the overdrive light doesn’t come on when you press the O/D button. 

Most of the time issues for a car’s overdrive come down to the vehicle’s transmission or an electrical issue. Possible causes for overdrive not switching on:

  • Faulty transmission range switch
  • Valve body
  • Faulty overdrive brake
  • Faulty ECM

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Overdrive Diagnostics & Part Replacement in Hamilton

If you’re having issues with your car’s overdrive it will likely need an electronic scan and paid diagnostic to find out the issue. For overdrive fixes, you will need to take your car to a qualified mechanic. For any of your overdrive diagnostics or issues come to Grimmer Motors.

You can trust the experienced mechanics at Grimmer Motors will be able to diagnose your overdrive issue, fix it or organise the service for you. 
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