#Laycock overdrive squeak manual#

With the cone clutch engaged (normal operation) the output of the gearbox fed directly to the propshaft. The overdirve unit contained a cone-clutch assumbly incorporating an epicyclic geartrain.

#Laycock overdrive squeak manual#

The old-style 'overdrive' units fitted to manual transmissions were a separate unit bolted to the back end of the gearbox. On most modern cars, including autos, the top gear is typically 0.75:1 - i.e. Overdrive just means that the gear ratio is below 1:1. People who only experience so-called overdrives on automatics don't realise the fun they are missing! The latter is better for doing intermediate changes, eg 3, 3 1/2, 4,5. It can indeed be on the steering column (Triumph 2000 Mk1) or on the gearlever. The joy of having an overdrive, as opposed to an ordinary 5th gear, is that you don't have to declutch and then make a staggered shift from 4/5 or 5/4 - you just flick a switch. In these cases it adds an extra ratio about half way between 2/3 and 3/4, as well as a 5th. The older kind of 'genuine overdrive' not only adds a 5th gear to an ordinary 4 speed manual box, it can in some cars be engaged in 3rd (as in my Triumph 2000), or even in 2nd (eg TR sports cars). It has its uses, but it doesn't actually add an extra gear. The kind discussed here is, as others have said, merely a 4th gear lockout, on an automatic. Moonshine is right - the two kinds of 'overdrive' are entirely different. Why have an overdrive switch? - Cliff Pope