Automatic gearboxes
Troubleshooting and fixing autobox problems.
With automatic gearboxes packing an increasing number of ratios, they can go wrong with expensive consequences. Rob
Marshall investigates their inner secrets and how their lives can be prolonged.
Before US decadence is blamed for the ‘lazy-man’ automatic transmission, consider that changing gear was not as easy on 1930s manual cars compared to those of today. While those early, bulky automatic transmissions worked fine with big American V8s being driven on wide open highways, they did not translate well initially, when fitted to sub-2.0-litre European four-cylinder engines that had to make swift overtakes on busy two-way roads. This explains the initial scepticism with which the ‘slushbox’ was met by British motorists, many of whom felt that they not only robbed the driver of control, but were also uneconomical and sapped power from the engine.
Gaining acceptance
Early automatic gearboxes were so bad at deciding the appropriate moment for ratio shifts that some initial European applications left the task of changing gear to the driver. On certain types, such as the Wilson pre-selector, one could select the next gear with a small hand lever and the ratio change would be made by depressing a foot pedal, which released a brake band that was wrapped around the outer ring gear of the appropriate epicyclic gear set within the gearbox.
The arrival of sophisticated electronics, especially the self-learning ECUS that were pioneered by Japanese manufacturers from the 1980s, made the transmissions more responsive. Most subsequent developments have focused on making the unit lighter, less wasteful, cheaper to produce and more compact, especially for front-wheel drive vehicles.
In the late 1990s, when carbon dioxide emissions and fuel economy figures were chosen as the means by which car owners and manufacturers could be taxed/ penalised, automatic gearboxes were still relatively inefficient, compared to manuals. The arrival of single- and twin-clutch automated manual gearboxes has accelerated automatic transmission development, with makers of the latest types boasting that they have caught-up in the efficiency stakes. As automated manual gearboxes face their own problems, chief among which are relatively poor reliability and high costs, it is believed that the traditional torque converter clutch, coupled to an electronically-controlled, epicyclic-geared transmission, on which this feature focuses, will increase in popularity.