Its name is English and it is true that most of the cars that have offered an overdrive are English. But they are not the only ones since many manufacturers have understood the usefulness of the system for their cars. Falling out of use in the 70s, the Overdrive is much more than an old car gadget.
The context
We are at the end of the 1950s and the cars are starting to move forward again by introducing many technical innovations. But sometimes it is expensive. And that’s where Overdrive comes in. This system created by Laycock-De Normanville was successful simply because it was ingenious, useful, inexpensive… and rendered great service.
The purpose of the Overdrive was actually quite simple: to provide an overdrive transmission. At the time of its introduction, most 3 or 4-speed gearboxes offered a direct drive last gear. If it is a simple solution, it has the disadvantage of being ultimate, being able to be improved only by changing the gear ratios. With the addition of an overdrive, since it is a system that was added to the box already mounted “basic” on the car, we could go down below the 1 to 1 ratio and thus go faster on the same gear or, conversely, bring the engine down to revs.
A specific need, not only British use
The need for overdrive was felt when the English began to “arm themselves”. Small roadsters were popular, especially with American servicemen returning from Europe. Only, if their mechanics were evolving in the right direction by offering more and more consistent powers, the development was not the same with the gearboxes, clearly lagging behind with their 3 or 4 gears and their direct drive.
This is not necessarily a big problem when you ride at a good pace on small roads. But when you push the gears on major axes, staying high in the towers for a long time, it’s not ideal. The addition of overdrive therefore makes it possible to spin on these major axes while reducing the revolutions taken by the engine. As a result, this one is less in demand, but the driver wins twice: by driving because the sound volume goes down (and since these roadsters are already very noisy it’s a real plus) and then it also saves a little in consumption!
Models will vary depending on the uses. We can thus engage the overdrive only on the higher gear (the 4th gear most of the time) or, in some cases, from the engaged third gear.
In the register of the disadvantages we found the lack of recovery caused by an overdrive ratio, sometimes solved by the manufacturers and allowing to create a true-false kickdown when you pressed the accelerator which disengaged the overdrive but also a perfectible ergonomics since the switch to engage the system was not always ideally placed. It must be said that it was partially solved in the 60s and 70s when the switch was installed directly on the gear lever.
Regarding the applications, if we think directly of English cars, the overdrive was finally mounted on various cars. Thus, Volvo was very fond of it to the point that nearly a third of the overdrives were mounted on Swedish!
On the American side, even if the automatics were queens, some cars were equipped with them, like the Ford Thunderbird. In France, they have been found on Simca Featured (the Rushmatic) or on the Facel Vega equipped with Pont à Mousson manual gearboxes.
Note also other applications, even at… Ferrari! Thus the 250 GT 2+2 could receive an overdrive. It is true that the lack of dynamism of the system was counterbalanced by the fact that the car was more intended for pleasure than for great sport.
Overdrive has “saved” many cars. But technical development will eventually take over. Manufacturers will thus develop 5 boxes which will make the use of overdrives unnecessary during the 70s.