1970s Triumph 2000 - Whatever happened to 'Overdrive'?
JOGON
on 29 June 2011
Triumph 2000 - Standard transmission on the original car was a 4-speed manual gearbox, with Overdrive as an aption. Whatever happened to overdrive, or did we just get a 5th gear instead? Certain family cars, usually brown, had switch on the top face of the gear knob. From vague recollection you could click this on into overdrive and it was like going up a gear, without having to. In o/d 4th you could just click down/out to 'come down a gear' to eg overtake. Seemed hi tech at the time, presume some reason for demise, any ideas or mech explanations for a non engineer.
Comments
Vitesse6 on 29 June 2011
You were right in thinking we got 5 gears instead. The overdrive was a separate unit on the back of the gearbox with an epicyclic gear set in it.
I have one on the Vitesse and as you said flick the switch to engage and you get an extra gear when in either 3rd or 4th. Makes for easy driving in towns as you can flick between overdrive 3rd which is pretty much like ordinary 4th and overdrive 4th which equates to 5th without using the clutch or gear lever.
gordonbennet on 29 June 2011
Had it on a 69 Ventora, mind you it only needed one gear as it would pull from 10mph in overdrive top all the way through without a hiccup...the micro switch must have been faulty as it worked on every gear not just top.
Our 93 Volvo 940 td estate had overdive too, still works fine in the not so careful (maintenance free zone.;) hands of my sister...you wouldn't believe how many times we've kicked ourselves for selling it on, agriculturally simple to fix and it still hasn't rusted anywhere.
unthrottled on 29 June 2011
The epicyclic unit was an added complication (expense), and was bulkier and mechanically less efficient than simply adding an extra gear onto the layshaft. They do have advantages though and a lot of trucks still use them for 'splitter' gears.
They have a niche following with the muscle car crowd because it is possible to run the quarter mile with only one cluth depression which gains a valuable couple of 10ths.
Pyranha on 30 June 2011
Overdrive was a reasonably popular addition to older Landies. My SIII 109" had it, but on that is was an extra gear stick like the low range transfer box, rather than a switch, so there were 3 gear sticks to play with (normal, low range and overdrive), as well as the 'engage 4 wheel drive' knob. It meant I had 20 gears - 16 forward and 4 reverse (not that overdrive was a particularly useful addition to low range!)
craig-pd130 on 30 June 2011
I used to enjoy the sequence on my old BGT: 3rd to OD 3rd, then 4th to ODth.
Although as standard, the Laycock OD unit scarcely changed any faster than a conventional gearchange .... alled to the fact when I got the car, the previous owner had mistakenly filled the gearbox with EP90 which, when warmed up, caused the friction material in the OD unit to slip :-/
Bobbin Threadbare on 30 June 2011
www.autotrader.co.uk/classified/advert/20111038131...p
Overdrive is still out there..!
RT on 30 June 2011
In the '70s after the first oil crisis, I remember Motor magazine using a O/D-equipped Triumph 2000 to test the effect of overall gearing on fuel consumption. The result showed that a 10% increase in overall gearing gave a 5% improvement in fuel economy.
It was inevitable that O/Ds would be superceded by 5+speed gearboxes, both manual and automatic where top gear is very overdriven to minimise fuel consumption.
jc2 on 30 June 2011
On many modern cars(particularly FWD)fourth gear is overdriven(less than 1 to 1) let alone fifth.
Ethan Edwards on 30 June 2011
Still out there.
My 03 2.5 XTrail Auto is a three speed auto with a 4th being overdrive (small silver button on side of the gear selector).
My 2010 Nissan Note 1.6 Auto again a small button on the side of the gear selector selects...yep you guessed it - overdrive.
These are all standard equipment.
Sofa Spud on 30 June 2011
As others have said, 5-speed gearboxes, and more recently 6-speed ones, as on myVW Touran TDI, serve the same purpose as planetary overdrive units, but using extra normal gear sets in the gearbox instead.
Someone mentioned the overdrive units that were available for 'Series' Land Rovers. There was an overdrive unit made to fit the later coil-sprung Defender type Land Rovers too, but I don't know if it's still available - I never saw one thus fitted so they must have been rare.
Many heavy lorries have extra gearing that operates by a switch - e.g splitters, which split each gear into hi and lo, either using using a planetary auxiliary box or, in older designs, a 2-speed unit incorporated in the final drive (2-speed axle). Others used a range-change, where the button shifted from lo to high range, so you go through all the gears in lo, then again in hi, although normally you miss some out . I believe a lot of modern top-weight lorries now have sequential boxes, where you just nudge the lever forwards or backwards to change up or down a gear, though.
jc2 on 30 June 2011
Two-speed axles were available on some cars as well as on commercials.The overdrive used on L/Rovers was also available other vehicles-100E at one time.There were other makes of overdrive available at different times-for example,Mk.IV Granadas had it as an option.Some overdrives could freewheel,giving you clutchless gearchanges.
turbo11 on 30 June 2011
During my Apprenticeship at GKN Laycocks (formerly Laycock De Normanville) who manufactured Overdrives, I built dozens, if not hundreds of them. The company was based in Sheffield and folded two years after I completed my Apprenticeship and left. I could see the technology was outdated and the company was struggling so I left and went into F1. When I visit Sheffield, I still drive past the old site which is now a supermarket, petrol station, Mcdonalds and Audi dealership(says it all about our manufacturing) The foundation stone marking the opening of Laycocks is still there.
RT on 30 June 2011
Still out there.
My 03 2.5 XTrail Auto is a three speed auto with a 4th being overdrive (small silver button on side of the gear selector).
My 2010 Nissan Note 1.6 Auto again a small button on the side of the gear selector selects...yep you guessed it - overdrive.
These are all standard equipment.
Is that because they use an ancient Jatco autobox with only three speeds?
unthrottled on 30 June 2011
The whole 'overdrive' thing is a moot point-unless you keep final drive ratios identical. BMW used to put 5th gear as direct, with 1-4 being underdriven. I don't recall anyone complaining abut bimmers being short legged.
Ethan Edwards on 30 June 2011
No idea. I doubt that they use the same gearbox though.
One's a 4x4 and the others a small city hatchback.
The basic boxes are three speed but with the o/d it's four speed. It just works and works well so I'm not over bothered about if it's 'modern' or not.
475TBJ on 30 June 2011
Overdrive made TR3A a 7 speed, unless my memory is playing tricks on me.
Glaikit Wee Scunner {P} on 30 June 2011
Father had a couple of Rootes group cars with overdrive. A 1967 Humber Sceptre followed by a hot Sunbeam Rapier H120. They had overdrive on 3rd and 4th gear only-apparently because of torque limitations. The London to Sidney rally Triumphs and the winning Hillman Hunter did have overdrive capability on all forward gears- perhaps to maximise the hillclimbing speed in the mountains?
unthrottled on 30 June 2011
Father had a couple of Rootes group cars with overdrive.
To buy one Rootes group car could be considered unfortunate...!
Reminds me of a friend who had three (3!) Marinas. One imagines the thought process: "I know the first two were rubbish but perhaps this one will be different. Damn, it's the same."
Edited by unthrottled on 30/06/2011 at 16:55
unthrottled on 30 June 2011
An separate overdrive unit only really makes sense if it applies to more than one gear-this way the the number of gears in constant mesh can be reduced without sacrificing the total number of ratios.
in automotive applications, it would make a lot of sense to mate a wide ratio 4 speed to a range change. Theoretically this would 8 speeds, but overlap would effectively reduce this to 6-plenty for a car.
It would be advantagous because of the way people drive. Most people are not very good at downshifting and don't use the engine or the box to their full potential. This tends to cause people to buy an engine that's bigger than they really need to make sure that they have adequate acceleration at low engine speeds-which is silly. If you data log the power* requested by the driver, you'll almost always find that they request less than ~30hp for 75% of the time, with brief excursions of over 100hp for sharp acceleration. A pneumatic range change could smoothly switch the engine from 2000 RPM to 4000RPM which would give great cruising economy and maximum acceleration potential when required, rather than the leave-it-in-fourth fudge which gives neither.
*engine output torque is almost completely irrelevant and mantras like 'torque wins races, horespower sells cars' should be dismissed as illiterate.
Edited by unthrottled on 30/06/2011 at 17:15
832ark on 1 July 2011
>>Makes for easy driving in towns as you can flick between overdrive 3rd which is >>pretty much like ordinary 4th and overdrive 4th which equates to 5th without using >>the clutch or gear lever.
Run that past me again - I think it'd be pretty hard to shift between o/d 3rd and o/d 4th without moving the gear leaver! Between 3rd and o/d 3rd or 4th and o/d 4th then fine
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