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, as many manufacturers have understood the usefulness of the system for their cars. Since Overdrive fell out of favor in the 70s, it is much more than an old car gadget.
We are at the end of the 1950s and the cars are again starting to move forward by introducing many technical innovations. But sometimes it is expensive. And this is where Overdrive comes into the picture. This system created by Laycock-De Normanville was successful simply because it was brilliant, useful, cheap … and provided a great service.
The purpose of Overdrive was actually quite simple: to provide an overdrive transmission. At the time of introduction, most 3- or 4-speed gearboxes offered a direct drive final gear. If it is a simple solution, it has the disadvantage of being ultimate, as it can only be improved 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 just British use
The need for exaggeration was felt when the English began to “arm themselves”. Small roadsters were popular, especially among American soldiers returning from Europe. Only if their mechanics developed 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.
It is not necessarily a big problem when you drive at a good pace on small roads. But when you’re pushing the gears on big axes and staying high in the towers for a long time, it’s not ideal. The addition of the overdrive therefore makes it possible to spin on these main 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 volume decreases (and since these roadsters are already very noisy, this is a real plus) and then it also saves a little on consumption!
The models will vary depending on the application. Thus, we can only activate the overdrive in the higher gear (4th gear most of the time) or in some cases from the engaged third gear.
In the register of disadvantages, we found the lack of recovery caused by an overgear ratio, sometimes solved by the manufacturers and allowing to create a true-false kickdown when you pressed the accelerator, which disengaged the overgear, but also a perfect ergonomics, since the switch to the engage system was not always ideally placed. It must be said that it was partially solved in the 60s and 70s when the switch was mounted directly on the gear stick.
Regarding the applications, if we think directly about English cars, the overdrive was finally fitted to various cars. Thus, Volvo was very happy with it to the point that almost a third of the overdrives were fitted in Swedish!
On the American side, although automatics were queens, some cars were equipped with them, like the Ford Thunderbird. In France they have been invented Simca highlighted (Rushmaticen) or on 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 system’s lack of dynamism was offset by the fact that the car was intended more for pleasure than for great sport.
Overdrive has “saved” many cars. But technical development will eventually take over. The manufacturers will thus develop 5 boxes, which will make the use of overdrives unnecessary during the 70s.