I think this applies mainly to older auto' gearboxes - my car has an overdrive that can be switched on or off from a button on the gear lever. My question is why have the switch? On my car the overdrive switch doesn't seem to do much more than to enable a fourth gear on the 'box. Why not have it on all the time? It doesn't seem to effect the other gears. Is it just a gimmick or am I missing something?
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My Almera has just such a thing. I like the switch because it's a smaller hand movement than using the gear lever, plus with the switch there's no chance of accidentally chnaging into neutral when it's time to re-engage a higher gear.
My only complaint about the overdrive switch is that I'd lke one on the steering wheel too. If they can put the audio controls there, why not the overdrive?
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Useful to stop 'hunting' on a winding road or one with an incline. Also useful to help keep to 30mph limit.
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Do I understand then Aprilia that it isn't really an overdrive but a top gear lock?
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Overdrive switch? on an Almera?
Is this true?
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TourVanMan TM < Ex RF >
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"Overdrive switch? on an Almera?
Is this true?"
Yes - I can confirm this. SWMBO has a 1.8 auto with such a button.
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I had - many many years ago - a Triumph 2.5PI which had overdrive engaged by a switch on top of the gear lever. iirc push forward to disengae, pull back to engage. Overdrive acted on 2nd, 3rd and 4th gears giving a 7 speed gearbox in 1973:-)
Great in fastmoving traffic for acclerating ...Action took about 1 second to happen but no clutch action required so no loss of power when changing.
Superb fun at 30mph in town as well for traffic light grand prix::-)
madf
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Just like madf I came across overdrive many years ago, about 34 years to be precise. Owned a Sunbeam Alpine sports with detachable hard top, plus overdrive on 3rd & 4th, which was operated by a lever off the steering column. Great for the reasons mdf gave and shows how far we have moved on in some areas, but not in others!
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It sounds as though there are two types of overdrive, all mine does is to 'activate' 4th gear, it doesn't affect the first three gears at all (not that I can notice anyway). If the overdrive is on it doesn't lock into 4th, it still changes gears up and down as normal. Car is a 1984 Mkii celica supra BTW.
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I've just thought of a better way to explain it - think of it this way round - it's a switch that stops the car changing up into fourth gear - therefore, what's the point?
Does the Almera work in the same way? I think Lud is right in that it isn't really an overdrive?
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The purpose does seem to vary. On my old 1968 Reliant Scimitar V6 coupé manual, I used the overdrive switch essentially to add a fifth gear although it did work on third as well as I recall. Fast forward 20 years and my automatic 1989 Honda Legend coupé had a square button which essentially pushed you back up into fourth when pressed if you had previously selected third for acceleration. It took you back down when pressed again. Only problem was that it was difficult to find on the console out of line of sight by the shift stick so it was really quicker to change gear using the stick without looking . I only pressed it now and again to make sure it was working and didn't think it half as useful as on the Scimitar.
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Moonshine is right - the two kinds of "overdrive" are entirely different. The kind discussed here is, as others have said, merely a 4th gear lockout, on an automatic. It has its uses, but it doesn't actually add an extra gear.
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). In these cases it adds an extra ratio about half way between 2/3 and 3/4, as well as a 5th.
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. It can indeed be on the steering column (Triumph 2000 Mk1) or on the gearlever. The latter is better for doing intermediate changes, eg 3, 3 1/2, 4,5.
People who only experience so-called overdrives on automatics don't realise the fun they are missing!
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Just spent 2 weeks in Florida with a Ford E350, full size 12 seater van. A very heavy beast even before it was fully loaded and the overdrive "off" switch came in very handy when slowing down as you had the benefit of increased engine braking without having to manually move the shift lever.
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Overdrive just means that the gear ratio is below 1:1. On most modern cars, including autos, the top gear is typically 0.75:1 - i.e. all cars have 'overdrive' now.
The old-style 'overdrive' units fitted to manual transmissions were a separate unit bolted to the back end of the gearbox. The overdirve unit contained a cone-clutch assumbly incorporating an epicyclic geartrain. With the cone clutch engaged (normal operation) the output of the gearbox fed directly to the propshaft.
With 'overdrive' engaged, a soleniod was energised via the little switch and this allowed oil pressure to disengage the cone clutch so that dirve was via the epicyclic geartrain giving a an 'overdrive' ratio.
This system avoided the expense and bulk of a 5-speed gearbox design and allowed 'overdrive' to be a bolt-on option. The best known units were the Laycock de Normanville units made in Sheffield (IIRC..?).
The little 'OD' switch on many auto's does indeed just lock out top gear - but since top is an 'overdrive' ratio they are correct to call it an overdrive switch. Most JAPCO and Aisin-Warner units have this facility.
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This system avoided the expense and bulk of a 5-speed gearbox design and allowed 'overdrive' to be a bolt-on option. The best known units were the Laycock de Normanville units made in Sheffield (IIRC..?).
GKN Make a system as a retro fit to LR Defenders... Expensive though
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The best known units were the Laycock de Normanville units made in Sheffield (IIRC..?).
Yes when we were kids my friends Dad used to work for Laycocks, they were on Archer Road in Sheffield.
www.overdrive-repairs.co.uk/about_us.html
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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),
My friends dad had a Triumph 2000 with the overdrive button on top of the gear stick. To me as a kid obsessed with cars (late '70's), having an extra gear you could select electrically was a gadget of James Bond proportions!
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>..we have moved onin some areas, but not in others!
It's probably much cheaper to have a fifth gear in the gearbox (and it will certainly take up less space) than to have an overdrive.
--
L\'escargot.
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When Toad the Supra is belting around certain places it is very handy just to switch out overdrive, letting the autobox look after the gear changing but avoiding unwanted changes into top when one lifts the throttle, losing engine braking and letting the turbos off the boil. The option is manual, which tends to demand a change when the rev limiter cuts in just when one is busy.
Overdrive for full song, of course.
Don't ask about mpg!
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