Question about overdrive

[adpsimpson]

Never had an automatic before, so I've got some learning to do here... as far as I understand, overdrive is simply the top gear - is that right? Does it mechanically link the input and output shaft in the Surf, bypassing the torque converter? If so, it must be much more efficient than the other gears - is there a way to tell if it is engaged? In fact, is it possible to tell which gear the box is currently in at all?

[MattF]

Overdrive will only kick in at around the 50 m.p.h mark, if I remember correctly, offhand. Before then, (and you'll notice when it kicks in), it serves bugger all purpose.

[adpsimpson]

you'll notice when it kicks in

You're assuming I know what to expect it to feel like here...! As for the other questions, what exactly is overdrive?

[Sancho]

Overdrive is the top gear. The purpose of switching it off is to stop the gearbox 'hunting' when you're going up and down hills and that sort of thing.

You are right about the direct link thing, but that's the torque converter 'locking up', which happens with or without overdrive. As Matt says, and going by both of my surfs, you know when that happens. There is kind of a dull 'thunk' and everything feels a bit smoother.

[adpsimpson]

You are right about the direct link thing, but that's the torque converter 'locking up', which happens with or without overdrive. As Matt says, and going by both of my surfs, you know when that happens. There is kind of a dull 'thunk' and everything feels a bit smoother.

Making sense, thanks. So once the torque converter is running steadily in any gear it locks - would that also explain why cruise control manages to make the engine behave much smoother than my humble right foot?

[Sancho]

Making sense, thanks. So once the torque converter is running steadily in any gear it locks - would that also explain why cruise control manages to make the engine behave much smoother than my humble right foot?

The torque converter locks up, then the overdrive comes in. It doesn't lock up in the two lowest gears. I think. I forget. It's been a while.....

The converter is probably locked by the time you put the cruise on. Mine always was.

[adpsimpson]

Grand, understanding.

So selecting 'L' on the gearbox keeps it to first gear, selecting '2' keeps it in (or below?) 2nd, hitting the 'OD off' button keeps it in 1-3 and having it in 'D' allows full use of all 4 gears... So... why not just have a 'L,2,3' series of positions on the gear selector, instead of separating out the final gear for special treatment via a button?

[Sancho]

Grand, understanding.

So selecting 'L' on the gearbox keeps it to first gear, selecting '2' keeps it in (or below?) 2nd, hitting the 'OD off' button keeps it in 1-3 and having it in 'D' allows full use of all 4 gears... So... why not just have a 'L,2,3' series of positions on the gear selector, instead of separating out the final gear for special treatment via a button?

Yes, L holds it in first, 2 in second, OD off will stop it going into overdrive, D allows all of the gears. On your last point: Because that arrangement would stop you from being able to lock it out of top gear and still use the others. The selections on the stick don't keep it 'below' a gear, they lock it into that specific gear. Mostly for towing and the like. Also good for engine braking when going downhill in the snow....

[adpsimpson]

Yes, L holds it in first, 2 in second, OD off will stop it going into overdrive, D allows all of the gears. On your last point: Because that arrangement would stop you from being able to lock it out of top gear and still use the others. The selections on the stick don't keep it 'below' a gear, they lock it into that specific gear. Mostly for towing and the like. Also good for engine braking when going downhill in the snow....

Thanks Sancho. Spent my lunch hour trying to get my head round auto gearboxes (dual sun planetary gear sets, eh? Amazing what you learn off wikipedia). Making more sense now.

[Sancho]

Thanks Sancho. Spent my lunch hour trying to get my head round auto gearboxes

It's a big metal thing and it's magic. That's all anyone really knows about them.

[darkdezigns]

quite easy to tell od is on,if its not you get a light on the dash,also at approx 55mph the revs will drop,ie into another gear just watch between 50/60mph

[Predictable Bob]

The rev drop between 50 & 55 is the box going into lockup - apparently it happens at lower speeds if your ATF is in good nick

[darkdezigns]

The rev drop between 50 & 55 is the box going into lockup - apparently it happens at lower speeds if your ATF is in good nick

ok boss

[B16mts]

Yes, L holds it in first, 2 in second, OD off will stop it going into overdrive, D allows all of the gears. On your last point: Because that arrangement would stop you from being able to lock it out of top gear and still use the others. The selections on the stick don't keep it 'below' a gear, they lock it into that specific gear. Mostly for towing and the like. Also good for engine braking when going downhill in the snow....

With all my auto's (including i'm sure the surf), when selecting say "2" it does use 1 and 2, but nothing higher. its been like that with all my cars, it doesn fix into that exact gear, just lets it go up to that one. still great for engine breaking when you're boiling your brake fluid down a big hill somewhere!

Martin

[Sancho]

With all my auto's (including i'm sure the surf), when selecting say "2" it does use 1 and 2, but nothing higher. its been like that with all my cars, it doesn fix into that exact gear, just lets it go up to that one. still great for engine breaking when you're boiling your brake fluid down a big hill somewhere!

Martin

I stand corrected. I've never noticed, but I guess I never tow...