2 Different Techie Q's.....
Discussion
1. What is overdrive? The learned few talk about 5th and 6th or just 6th being overdrive gear/s, and the ratio of less than 1:1 not being totally indicative of O/D.... So What IS O/D?
2. If an engine runs lean, then it can damage the engine - but what happens when you lift off/overrun - I thought modern engines killed all fuel supply under these conditions - presumably resulting in a VERY lean mix?
2. If an engine runs lean, then it can damage the engine - but what happens when you lift off/overrun - I thought modern engines killed all fuel supply under these conditions - presumably resulting in a VERY lean mix?
Well - overdrive is an extra gear, but it doesn't necessarily have to be 1:1 - its actually "over-driven" past 1:1 (hence the name). Quite a few Turbo Hydramatic transmission series have overdrives down into the 0.6:1 range.
And technically, the 6 speed T56 manual transmission on my ute has an "Overdrive" - its the 6th gear selection, which is really only usable after about 70 mph. Just because its selected by me doesn't mean its any less of an overdrive.
Unless you have to, always run your automatic in the overdrive selection - what this does is shift the car down to that fuel-saving overdrive gear when possible. The only time you don't want to use it is in situation where you will bog, or otherwise lose much-required power (such as in towing, where you could cause excessive engine/trans wear by overdriving while pulling a heavy load)
And technically, the 6 speed T56 manual transmission on my ute has an "Overdrive" - its the 6th gear selection, which is really only usable after about 70 mph. Just because its selected by me doesn't mean its any less of an overdrive.
Unless you have to, always run your automatic in the overdrive selection - what this does is shift the car down to that fuel-saving overdrive gear when possible. The only time you don't want to use it is in situation where you will bog, or otherwise lose much-required power (such as in towing, where you could cause excessive engine/trans wear by overdriving while pulling a heavy load)
Edited by drew ss on Tuesday 16th March 23:28
drew ss said:
Well - overdrive is an extra gear, but it doesn't necessarily have to be 1:1 - its actually "over-driven" past 1:1 (hence the name). Quite a few Turbo Hydramatic transmission series have overdrives down into the 0.6:1 range.
And technically, the 6 speed T56 manual transmission on my ute has an "Overdrive" - its the 6th gear selection, which is really only usable after about 70 mph. Just because its selected by me doesn't mean its any less of an overdrive.
Unless you have to, always run your automatic in the overdrive selection - what this does is shift the car down to that fuel-saving overdrive gear when possible. The only time you don't want to use it is in situation where you will bog, or otherwise lose much-required power (such as in towing, where you could cause excessive engine/trans wear by overdriving while pulling a heavy load)
And technically, the 6 speed T56 manual transmission on my ute has an "Overdrive" - its the 6th gear selection, which is really only usable after about 70 mph. Just because its selected by me doesn't mean its any less of an overdrive.
Unless you have to, always run your automatic in the overdrive selection - what this does is shift the car down to that fuel-saving overdrive gear when possible. The only time you don't want to use it is in situation where you will bog, or otherwise lose much-required power (such as in towing, where you could cause excessive engine/trans wear by overdriving while pulling a heavy load)
Edited by drew ss on Tuesday 16th March 23:28
Bloody Hell Andy. Did you get another hand? Or have you found the other keys on the board at last???
(Must have cut and pasted I suppose?)
mym8v8 said:
Bloody Hell Andy. Did you get another hand? Or have you found the other keys on the board at last???
(Must have cut and pasted I suppose?)
You're not kidding. He hasn't got that kind of grasp of the English language.(Must have cut and pasted I suppose?)
He got it from here - http://answers.yahoo.com/question/index?qid=200906...
mym8v8 said:
drew ss said:
Well - overdrive is an extra gear, but it doesn't necessarily have to be 1:1 - its actually "over-driven" past 1:1 (hence the name). Quite a few Turbo Hydramatic transmission series have overdrives down into the 0.6:1 range.
And technically, the 6 speed T56 manual transmission on my ute has an "Overdrive" - its the 6th gear selection, which is really only usable after about 70 mph. Just because its selected by me doesn't mean its any less of an overdrive.
Unless you have to, always run your automatic in the overdrive selection - what this does is shift the car down to that fuel-saving overdrive gear when possible. The only time you don't want to use it is in situation where you will bog, or otherwise lose much-required power (such as in towing, where you could cause excessive engine/trans wear by overdriving while pulling a heavy load)
google is ur friend mate
And technically, the 6 speed T56 manual transmission on my ute has an "Overdrive" - its the 6th gear selection, which is really only usable after about 70 mph. Just because its selected by me doesn't mean its any less of an overdrive.
Unless you have to, always run your automatic in the overdrive selection - what this does is shift the car down to that fuel-saving overdrive gear when possible. The only time you don't want to use it is in situation where you will bog, or otherwise lose much-required power (such as in towing, where you could cause excessive engine/trans wear by overdriving while pulling a heavy load)
google is ur friend mate
Edited by drew ss on Tuesday 16th March 23:28
Bloody Hell Andy. Did you get another hand? Or have you found the other keys on the board at last
now now gareth im not that bad am i...i could have just posted TRY GOOGLE
and as far as grasping the english language they teach us to use slang in australia so not so posh
Edited by drew ss on Wednesday 17th March 18:48
Edited by drew ss on Wednesday 17th March 18:49
Okay boys calm down! Yes, google would work, eventually. Wiki answers, er.... no!
To be specific re: the overdrive, I believe it was stevieturbo and granada203028 commenting on O/D. I'm sure G'man said " just because its under 1:1 doesn't make it overdrive..." which got me thinking... Granada203028 care to elaborate? Sorry but can't find the thread.
PS
Anyway, I thought we'd banned JFGI on here!
To be specific re: the overdrive, I believe it was stevieturbo and granada203028 commenting on O/D. I'm sure G'man said " just because its under 1:1 doesn't make it overdrive..." which got me thinking... Granada203028 care to elaborate? Sorry but can't find the thread.
PS
Anyway, I thought we'd banned JFGI on here!
I thought that the overdrive unit was fitted after the gearbox tailshaft, was swithable, and increased the overall gear ratio. Most cars that had overdrive could select it in third and fourth gears, they were sort of half gears. I had overdrive on my 1971 MGB. surely fifth and sixth gears are gears and not overdrive? sorry to confuse the issue, but is this correct.
north of watford said:
I thought that the overdrive unit was fitted after the gearbox tailshaft, was swithable, and increased the overall gear ratio. Most cars that had overdrive could select it in third and fourth gears, they were sort of half gears. I had overdrive on my 1971 MGB. surely fifth and sixth gears are gears and not overdrive? sorry to confuse the issue, but is this correct.
Whilst these were known as "Overdrive units" you're now getting into the realms of 'splitters.'You're MGB had an additional gearbox which was electrically operated. You say it was on third and fourth gears, but you could bypass the cut off, and make it work on all gears (though the additional gearbox was not strong enough to use the splitter in 1st and 2nd). Basically, it took the output and ran it through a 1:1 gear normally, but when switched to the O/D position would run it through an additional 0.9:1 (or similar) gear to lower the final drive ratio.
Wolfracer said:
1. What is overdrive? The learned few talk about 5th and 6th or just 6th being overdrive gear/s, and the ratio of less than 1:1 not being totally indicative of O/D.... So What IS O/D?
The strict definition of over drive in engineering is with a gear or pulley system where the output gear or pulley turns faster than the input one. Typical examples are push bike chain and car alternator drives.
When applied to car gearing though a better definition is a gear in which you have to be in a lower one to achieve maximum speed. For example in the manual Monaro and VXR8s, 5 and 6th are overdrive ratios in the gearbox but only 6th is an over drive as far as it matters to the driver.
High performance vehicles such as motor bikes and super cars may have over drive ratios in their gearboxes but the highest number one is still the gear for maximum speed. It is just the over all gearing which matters, not the split between primary reduction, gear box and final drive. Over drive units stem from the days when gearboxes were very simple with top 1:1 and over all gearing adjusted for maximum speed in top. So then tagged on over drive units were always for economy.
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