Image credit: (mechanics)#/media/File:Overdrive_Unit.jpg With the correct viscosity for a ‘splash’ lubrication method of distribution around the gearbox, coupled with a base oil that will not loose viscosity due to ‘shearing’ down under pressure our Duckhams SAE-40 will ensure you Overdrive gearbox will last for many thousands of miles yet to come. To that end it is essential that you select a high quality and stable oil and Duckhams classic car oils department recommends SAE-40, our mono-grade engine oil for all Overdrive gearbox applications. The disadvantage of this is that you are adding complexity to the Drivetrain including an electric solenoid used to engage the Overdrive, which could often be unreliable.įrom oil and lubrication points of view, the more gears and moving parts added top the system increases the work the lubricant must do to resist ‘shearing’ under the huge strain and pressures. Overdrives are one of the major reasons why we enjoy the classic car driving experience today with the flexibility that set up gives the spirited driver.
Furthermore, what better than an extra gear that could be utilised in between all other gears? Effectively making a 4-speed gearbox a 7 or even 8 speed. When fuel economy became a major priority for car manufacturers the thinking back then was that it was far easier and cost effective to utilise an external add on to an existing gearbox design rather than go to the effort of designing one from scratch. Why was the Overdrive used and what oil do you use?ĭeveloping gearboxes has always been a pricey business. Image credit: (mechanics)#/media/File:Triumph_Gearbox_without_Overdrive_-_2.jpg At first Overdrive would be available on just top gear but later models were able to offer capability on 2nd, 3rd and 4 th gears. When activated the overdrive engages to reduce the engine speed, relative to the driveshaft.
The gear set was activated by an electric solenoid and gave the driver a reduction in gear ratio at the flick of a switch or press of a button.
Laycock Products manufactured the units hence the name and they consisted of a planetary gear set in a bolt on unit between the main manual gearbox and driveshaft. Edgar de Normanville was the Brit responsible for inventing the Overdrive gearbox that became so prevalent amongst many of the iconic classic cars of the 1950s and 1960s.