PDA

View Full Version : Explanation of the overdrive button



iain_spen
20-07-04, 09:15
Hey, I'm still pretty new to Supras and was wondering...

1. Do you ever take the overdrive off?? because i dont :p

2. Does the TT have the same gearbox as the Turbo and N/A??

Snowman
20-07-04, 09:26
If you don't take the overdrive off you obviously aren't going fast enough!!!!

Not sure I would want to do over about 120 in 3rd gear! If you want to stretch its legs are make some big speed you are going to need 4th!

Ian R
20-07-04, 09:26
Think the boxes are the same.

IMO overdrive is very usefull in TT as it holds the revs longer in each gear which keeps the second turbo online can't say what difference it would make in a NA though

oxygene
20-07-04, 10:16
Originally posted by iain_spen
Hey, I'm still pretty new to Supras and was wondering...

1. Do you ever take the overdrive off?? because i dont :p

2. Does the TT have the same gearbox as the Turbo and N/A??
1. Yeah I do, how do you expect to piss on other road users without doing that...

2. Unsure, they other guyz are more knowledgable.

Jake
20-07-04, 10:24
Originally posted by Snowman
If you don't take the overdrive off you obviously aren't going fast enough!!!!

Not sure I would want to do over about 120 in 3rd gear! If you want to stretch its legs are make some big speed you are going to need 4th! :conf: huh?
Turning overdrive OFF would mean the car didn't get into 4th gear

Jake
20-07-04, 10:26
Originally posted by Ian R
overdrive is very usefull in TT as it holds the revs longer in each gear I don't think that's right Ian. I think you'll find that 'Overdrive Off' just stops it getting into 4th gear.

Jake
20-07-04, 10:30
Originally posted by iain_spen
Do you ever take the overdrive off?? Yes, to keep the revs in the range I want when driving fast and also I use it a lot for engine braking.

Snowman
20-07-04, 10:30
Jake

my bad wording perhaps would make more sense if said if you have the button pressed in and the o/D off light on then you aren't going fast enough. Need this O/D Off button to be "OFF"...not illuminated to engage 4th gear and thus have the higher speeds

attilauk
20-07-04, 10:34
1. yes i also knock it into 2 when im driving hard through the twisties or on some corners on track:cool:

2. afaik the boxes are the same

mawby
20-07-04, 10:57
Originally posted by Jake
I don't think that's right Ian. I think you'll find that 'Overdrive Off' just stops it getting into 4th gear. Indeed it isn't. All overdrive does is allow the 4th (aka overdrive) gear to be engaged. Turning overdrive off (so you get the o/d off illuminated on the dash) just prevents the box from using the o/d gear. Most useful when preparing to overtake I find as most overtake procedures can be done at less than 120mph! :D

Jake
20-07-04, 12:47
Originally posted by Snowman
my bad wording perhaps would make more sense if said if you have the button pressed in and the o/D off light on then you aren't going fast enough. Need this O/D Off button to be "OFF"...not illuminated to engage 4th gear and thus have the higher speeds Ah, gotcha now mate.

Aerotop Dave
20-07-04, 14:00
I never understood how it worked (even with the explanations in this thread) so I just leave it on so I don't get the annoying light on the dash.

mawby
20-07-04, 14:07
Originally posted by Aerotop Dave
I never understood how it worked (even with the explanations in this thread) so I just leave it on so I don't get the annoying light on the dash. That's probably cause a lot of people seem to think it's a magical button that makes the car go faster. It's really simple. An auto box goes 1st -> 2nd -> 3rd -> O/D (4th), having the "O/D OFF" turned on just causes the box to go 1st -> 2nd -> 3rd. That's it. Instead of 4 gears you now only have 3.

Aerotop Dave
20-07-04, 17:17
Okay, but I still don't get what it's actually for.

3 gears spread across the speed range suggests the car will rev higher in each gear with it turned off (3 gears spread across the rev range versus 4 gears means each gear has to handle a longer mph range?). But with my turned on it still revs to the redline when I mash my foot into the floor.

So if it revs to the redline with it turned on, why do I want to turn it off? If the light comes on with it's turned off, that suggests it should generally be left on.

Basically - I don't understand what it does, I don't understand why I'd want to turn it off, and the car seems to be telling me that I shouldn't turn it off!

:)

attilauk
20-07-04, 17:23
OVER DRIVE = 4TH GEAR
if you turn it off then you cant go into 4th gear
i usually use it to keep the car more stable when cornering hard at speed or to keep to 30 limits

mawby
20-07-04, 17:40
It doesn't affect the rev range at all. That's why with O/D Off you can't go above 120mph, cause that's only achievable in 4th gear.

Example 1

Amagine this, you're in a manual crusing along a nice stretch of single carriageway A-road. You come up behind a couple of lorries doing a far from acceptable speed. So you decide to overtake. You watch the on comming traffic, you see a gap about to approach so you drop it into 3rd to bring the revs/boost up, and as the last car passes you pull out and boot it. A perfect overtake.

Now amagine doing it in an automatic. You do nothing, as the last car goes past you pull out and kickdown. Can be very dangerous especially in the rain. You're pulling out in a high gear, then the car is changing down a gear, then you're shooting up the rev range probably engaging the 2nd turbo in the process. Then finally you have full power to overtake, by which time you've already (slowly) done half of the over taking. The reason I say it's dangerous is for the same reason you try to avoid the car changing down whilst going around a roundabout, you could lose the back end in the wet.

So, the what you do is turn off the overdrive. That drops the car into 3rd, which means you'll be higher up the rev range and hopefully have the 2nd turbo engaged in a controlled maner. When you pull out you instantly have all the power there at your disposal. No waiting for gear changes, boost increases etc.

Example 2

Imagine you're on some twisty roads and having some fun. In a manual you'd probably keep it in 3rd, only chaning down to 2nd for tight corners and only going into 4th+ for long straights.

What happens in the auto, you accellerate up to a corner, take your foot off to go round the corner and it changes up a gear. You put your foot down coming out of the corner and it changes down gear up, then up, then down, always changing between 3rd and O/D. Turning O/D off prevents this, it also give some engine breaking when entering the corners, and means you have more power there when coming out of them. If you reach a slow corner then it will still drop down into 2nd, just like you would in the manual.

Example 3

Touched upon above really. You're going down a steep hill. In a manual you could put it into 3rd to get lots of engine breaking to make the decent at a safer speed without over heating the breaks. In an auto you can turn off O/D to achieve the same thing.

Does that help?

Piran
20-07-04, 17:45
hmmm, looking at the Resources -> Technical Reference section I found this (http://www.mkivsupra.net/resources/automanual.html)

mawby
20-07-04, 17:49
Licked document by Piran
But if you disable the overdrive (will be indicated by a light in the dash) then the car is allowed to rev further before the box changes up a gear. I'm sorry but that's just wrong, unless someone can prove otherwise?

Piran
20-07-04, 17:56
I'm just quoting some Supra resource I found on the web somewhere :flame Dev :)

mawby
20-07-04, 17:59
Originally posted by Piran
I'm just quoting some Supra resource I found on the web somewhere That's fair enough mate. :) I remember the last time this was discussed I went out and tested it and it's not true. I can hit red line in standard auto mode with O/D on, so the suggestion that O/D off allows higher revs is obviously wrong.

Aerotop Dave
20-07-04, 19:47
Yeah, that's what I said above - I leave it on all the time and it still goes to the redline.

Cheers mawby, that's about the clearest explanation I've ever seen for the overdrive, and it clears up a few old wive's tales in the process.

One for the FAQ section methinks.

:thumbs:

Ian R
21-07-04, 02:47
Maybe its my imagination but when i've got o/d off my car seems to change just before redline 1 -3 normally and around 5000rpm when o/d is on normally take car right up to redline in 3rd put the o/d on and can feel it kick into 4th when i'm really gunning it down a dual track however in normal town driving it doesn't seem to make any difference apart from not selecting 4th. But as I said it might be my imagination so will make a point of looking at rev counter next time I do it

iain_spen
23-07-04, 11:03
bugger! my head is hurting now :(

Jon ERST S2
26-07-04, 23:30
the way I see it you will hit red line but you'll be in 3rd gear, concequently doing a slower speed.

See http://www.gearboxman.co.uk/content/gearspeeds.xls

Is for manuals but you get the idea.

carl0s
31-07-04, 14:18
Originally posted by Ian R
Maybe its my imagination but when i've got o/d off my car seems to change just before redline 1 -3 normally and around 5000rpm when o/d is on normally take car right up to redline in 3rd put the o/d on and can feel it kick into 4th when i'm really gunning it down a dual track however in normal town driving it doesn't seem to make any difference apart from not selecting 4th. But as I said it might be my imagination so will make a point of looking at rev counter next time I do it

it's just how hard you press the accelerator. The harder you want to accelerate, the later it'll change up. If you're being gentle it'll change dead early.

SUPRA2000
06-08-04, 11:52
does anyone know what the button behind the accelerator does

carl0s
06-08-04, 11:53
you answered it in the subject. Kickdown. It causes the box to kick down to the lowest gear it can.

SUPRA2000
06-08-04, 12:56
cool thanks

mawby
06-08-04, 13:17
Originally posted by carl0s
you answered it in the subject. Kickdown. It causes the box to kick down to the lowest gear it can. Is that true? Only reason I ask is my auto box will kickdown if I just move the accellerator quickly, I don't need to floor it for it to happen. Unless of course this courses the special Supra 2 gear kick down?

carl0s
06-08-04, 14:01
yep, it's like the kick ALL the way down button.

iain_spen
12-08-04, 19:25
are we talkin about the red button here?...

carl0s
12-08-04, 19:27
no. we're talking about the one that says "O/D Off" next to it.

The red button allows you to pull the J-Specs out of park with the engine off, or something.

UK spec doesn't have it.

iain_spen
12-08-04, 19:33
christ! I started this post and it's doing me head in now.

From a bit of experimenting with the O/D i've come to the final conclusion:

O/D on - the car feels faster and gets into 4th gear
O/D off - the car doesnt accelerate as fast and can't reach the top speed

does this sound about right???... :conf:

carl0s
12-08-04, 19:36
no, it's pretty friggin simple.

O/D Off, turns Overdrive off. (honestly, it does)

Overdrive is the fourth gear. It's called an overdrive gear because the gear ratio is greater than 1:1. Instead of reducing the gearing, it increases it.

iain_spen
12-08-04, 19:39
hang on then.... if O/D off disables 4th gear then surely im right in saying the car will drive slower with it off???... :conf:

my car just feels noticebly slower with the O/D off

carl0s
12-08-04, 19:40
the car won't reach top speed!! It'll redline in third gear.

iain_spen
12-08-04, 19:41
thats what I said!

carl0s
12-08-04, 19:41
fair enough :D
You kind of did, but you said it doesn't accelerate as fast !! :P

iain_spen
12-08-04, 19:49
it's just feels slower at accelerating when the overdrive is off... may be it's just me lol :p

carl0s
12-08-04, 19:55
overdrive is a pain if you're doing around 50mph and are on/off the accelerator. It constantly drops back into overdrive and then back out again. Times like this, you turn overdrive off and it stays in third ready for you to accelerate again.

Jake
12-08-04, 20:26
Originally posted by iain_spen
it's just feels slower at accelerating when the overdrive is off... may be it's just me lol :p Are you sure you aren't confusing the Overdrive button with the MANU button? The MANU button will make the car accelerate a lot slower because the car is (pretty much) stuck in 3rd gear.

Terminator
05-10-04, 15:53
Originally posted by Jake
Are you sure you aren't confusing the Overdrive button with the MANU button? The MANU button will make the car accelerate a lot slower because the car is (pretty much) stuck in 3rd gear.

It will only be stuck in third if that is where you leave the stick.

mawby
05-10-04, 15:58
Originally posted by Terminator
It will only be stuck in third if that is where you leave the stick. You mean if you leave it in Drive. Although it will still change down to 2nd if you come to a stop whilst in Drive and manual mode.

dangerous brain
06-10-04, 16:15
I've found a distinct difference in acceleration rates in any given gear from any given comparable rev range between manual mode and normal mode. My car doesn't seem to go as well sometimes in manual mode. No its not because I am lower down the rev range as I did say comparable revs in comparable gears.

If for instance I am accelerating with foot flat to the floor and say approx 4500 rpm lets say in 2nd in manu mode, it feels a touch sluggish. Depress the manu button to reselect normal mode and it will noticeably pick up a lot better. Its only seemed to do this since I fitted my delimiter. I get a flat spot around a ton as well.

Could be down to different speed sensors on individual boxes cause differing results.

Either way O/D is just an extra gear and has no effect on the rev range of any of the other gears. If you really want to prove it to yourself, go down the road in manu and record the speed that you hit the redline at in 1st 2nd and 3rd. Then doing max accellerate record the the speed you hit the redline at in 1st 2nd and 3rd again. There will be no difference. If you still doubt then also push the O/D button to off and repeat test. O/D won't come on in manu mode.

deepcom
17-10-04, 18:23
Here's one to consider then -

As the O/D doesnt function in manual mode, (yeah you can switch back to auto, automatically get O/D, then switch back to Manual to maintain the O/D until you accelerate sharpish when it switches back to 3rd and then coz your in Manual it stays in 3rd), can you actually get overdrive to come on in manual mode without having to switch back to auto ?

Anyone got any ideas about wiring a switch to the auto ECU so that you can manually engage overdrive by pushing an extra button when in manual ? (Would it be possible to wire a switch to the O/D actuator so instead of the auto ECU saying "switch to O/D" you simply have a button you can press ?)

And assuming that is possible am I correct is saying that O/D is actually 3rd gear with another cog engaged so you actually get 3rd gear cog + O/D cog engaged simultaneously to give overdrive ? And if so with a manual O/D activation switch would it then be possible to engage the O/D in the other gears as well in effect making the auto box 6 speed ????

Your thoughts are appreciated on this one.

Andy.

carl0s
17-10-04, 18:57
Overdrive is just fourth gear. The only reason it's called Overdrive is because its ratio is lower than 1:1

I'm sure the sixth cog on the 6sp'd is also an overdrive gear.

Rays the roof
27-04-05, 05:43
Are you sure you aren't confusing the Overdrive button with the MANU button? The MANU button will make the car accelerate a lot slower because the car is (pretty much) stuck in 3rd gear.

Not nessa celery true. Fastest 1/4 mile in an NA auto is achieved by starting in Manual with OD light illuminated and gear stick in first, foot to the floor taking it up a gear just before the red line (timing is essential) and then at 78 - 80 flick both Man and OD buttons, again timing is critical. Read all the previous threads in this post agree with some, but not all points. TRY it at Pod and prove your self wrong!!

:respekt:

carl0s
27-04-05, 08:28
Not nessa celery true. Fastest 1/4 mile in an NA auto is achieved by starting in Manual with OD light illuminated and gear stick in first, foot to the floor taking it up a gear just before the red line (timing is essential) and then at 78 - 80 flick both Man and OD buttons, again timing is critical. Read all the previous threads in this post agree with some, but not all points. TRY it at Pod and prove your self wrong!!

:respekt:

he's referring to off-the-line acceleration with the stick left in 'D'. If MANU is enabled while in D, take-off will be slow 'cause the car will skip 1st gear.

Supraman
28-04-05, 00:00
no. we're talking about the one that says "O/D Off" next to it.

The red button allows you to pull the J-Specs out of park with the engine off, or something.

UK spec doesn't have it.

Yep! It's basically for when you breakdown or want to jump start an auto.

OR

It's an eject button for the passanger seat in an aerotop...that always gets a worried look from the passanger! :eyebrows:

mawby
10-05-05, 18:49
Not nessa celery true. Fastest 1/4 mile in an NA auto is achieved by starting in Manual with OD light illuminated and gear stick in first, foot to the floor taking it up a gear just before the red line (timing is essential) and then at 78 - 80 flick both Man and OD buttons, again timing is critical. Read all the previous threads in this post agree with some, but not all points. TRY it at Pod and prove your self wrong!!Also worth noting that the NA box handles totally different to the TT. I've owned both and the NA has some of the 'normal' auto box features of changing up gear early and not changing down very quick. I can easily believe the NA needs to be run in manual mode to get a quick time down a strip. The TT is a different matter though.

mawby
10-05-05, 18:50
Yep! It's basically for when you breakdown or want to jump start an auto.Not sure I understand that. If you're jumping the car don't you just leave it in park?

Jarl Ayari
23-10-07, 20:14
Didnt think you could jump an auto??? I like the idea of the manually selected OD in manual mode, must be someone out there who could work it out...

dangerous brain
24-10-07, 00:27
Holy thread resurrection batman. I have manually selectable OD on my car :D Oh thats cos I have an aem :D

Jarl Ayari
24-10-07, 08:24
Thats the problem with newbies like Me. Old threads are a wealth of useful information.

Andi

dangerous brain
24-10-07, 11:09
Its not a problem at all. Way better to ressurect than start a new thread and get shouted at for not searching lol :D

AndrewOW
24-10-07, 11:32
Thats the problem with newbies like Me. Old threads are a wealth of useful information.

Andi


Well done. You passed the first test of the newbie :)

I don't know why you would want a manual overdrive selection in MANU mode.

When I want to do a little spirited driving etc, I keep O/D on, and press the MANU button on. This will drop the gearbox into 3rd, and then if you need more control over revs etc, you can then 'manually' drop the stick to 2nd or even 1st if nessa celery (I read it all too!). Push the gear stick through the box, like you would in a manual, and then if you do want to engage O/D, just turn the MANU mode off. Depending on the speed/revs the gearbox will then change up to O/D (4th) to enable top speed potential.

I hope this isn't too confusing, but I use it all the time, and its very effective, as I can cruise around all day in total auto, or knock it into MANU and give it some, depending on the road conditions, of course!

:)

dangerous brain
24-10-07, 12:01
The manu selection of o/d on and off is very useful if for instance you hit speeds over 120 regularly. Instead of hitting two buttons ie O/D on and then manu off you just hit the O/D button and leave the manu well alone.
A secondary use is if you cruise at like 45-50. If you have a manually selectable O/D you can force it to stay in 4th rather than continually dropping down every time you breath on the accelerator it stays in 4th right up until the ecu deems the engine cannot sustain itself so smoother driving and better economy.

AndrewOW
24-10-07, 12:20
I understand what you mean. I think its what you get used to doing (I like to do the gear change myself), but I do like the idea of keeping it in 4th (O/D) without the kickdown, as you mention.

dangerous brain
24-10-07, 12:28
I do the gear change myself. by stick L-2-D-push the O/D button 4th easy as that.

AndrewOW
24-10-07, 13:43
There you go Andi, a few workable options for you to choose from :)

redana777
27-02-11, 15:44
This one is right, o/d on
jake

my bad wording perhaps would make more sense if said if you have the button pressed in and the o/d off light on then you aren't going fast enough. Need this o/d off button to be "off"...not illuminated to engage 4th gear and thus have the higher speeds

RobSheffield
27-02-11, 15:59
This one is right, o/d on

Thanks for that, we had been so worried for the past 7 years!

scotty71
27-02-11, 15:59
A four year resurection for your first post :D

Oh and welcome ;)

redana777
27-02-11, 16:20
:d


Thanks for that, we had been so worried for the past 7 years!

redana777
27-02-11, 16:21
Thanks.


A four year resurection for your first post :D

Oh and welcome ;)

winnie109
17-05-11, 15:13
That's probably cause a lot of people seem to think it's a magical button that makes the car go faster. It's really simple. An auto box goes 1st -> 2nd -> 3rd -> O/D (4th), having the "O/D OFF" turned on just causes the box to go 1st -> 2nd -> 3rd. That's it. Instead of 4 gears you now only have 3.

That's got to be the most straight forward and simplist answer EVER!

Nicko
22-03-12, 23:36
Just leave it in O/D i havent really noticed a difference in petrol usage but as someone keeps saying i keep mine at 120 all the time :D

tony tt
23-03-12, 00:09
That thread was started in 2005 haha last post May 2011 dude!

Busemannen
31-08-17, 06:00
Is it possible to wake up this thread from the long forgotten past, as the information there is of importance even in 2017?... How long is the longest timespan any thread here on the forum has lived?