Auto Gearbox Question

[Baldchap]

Hey all.

I've got a question that's been niggling me for a while.

In a manual, the adage 'brakes to slow, gears to go' is justified, because banging the car down a couple of gears with the sole purpose of slowing down puts a fair bit of strain on the drivetrain and wears the clutch prematurely...

Now, in my automatic IS250 I've got the 'manual' option on the paddles and stick (or at least manual selection of the highest gear it'll go into) which is fantastically useful for holding speed on slopes and general boy-racery if I'm in that sort of mood.

My question is, as I'm trolling up to a steep downhill, if I simply bang the stick across from full-auto to paddle-icious and select 3rd, say, will this process harm my transmission in the same way it could a conventional manual? There's no physical connection and the TC clearly allows slip in the non-driven direction or overrun wouldn't happen, but there is quite clearly a difference in the drivetrain between ratios or there'd be no engine braking.

What's the answer? Brakes then gears as per IPSGA (as you would/should in a conventional manual), or just bash it down without a care?

[Exiled]

That is a good question as I do exactly as you do with regard to the "steep downhill" bit.

I don't know the answer but I'm sure it won't be long before someone comes along who does.

( I suspect a bollocking is on it's way)

[Baldchap]

Well it is 'bad driving' in any car, so the bollocking's deserved! I'm just wondering whether it's physically harmful to the car...

[TigerFish]

Why is it bad driving? You are in a gear suitable for the conditions. I've always been taught to use the gears on steep declines as overheating your brakes and them fading to useless by the bottom of the hill is much less desirable.

[ACLex]

Why is it bad driving? You are in a gear suitable for the conditions. I've always been taught to use the gears on steep declines as overheating your brakes and them fading to useless by the bottom of the hill is much less desirable.

+1 on that :)

Andy

[juicestop]

My IS250 Auto drops down a couple of gears 'automatically' when on a steep decline, no need to do it 'manually' - clever stuff :)

[Simon_D]

How does it do that? I remember someone telling me that my Subaru's gearbox should do the same but neither that nor the IS change down when going down steep hills. Is there a setting you need to be in?

I sometimes change down manually but, to be honest, there is so little engine braking from the IS250 engine that it's hardly worth it. I suppose anything to give the overworked brakes a helping hand is a good idea though.

[Baldchap]

The bad driving bit is not being in the right gear for the hill (which is good driving), but using the gears specifically to slow down instead of the brakes, rather than slowing down then selecting the correct gear (which is the correct approach).

Hope that makes sense. Thinking in terms of the Roadcraft system used by advanced bodies and the police it's Speed then Gear.

So any answers? Does boshing it down a couple of gears (in exactly the way I've just said I shouldn't) to slow cause harm to the auto transmission then way it would in a manual (excluding clutch wear, obviously)?

[juicestop]

How does it do that? I remember someone telling me that my Subaru's gearbox should do the same but neither that nor the IS change down when going down steep hills. Is there a setting you need to be in?

I sometimes change down manually but, to be honest, there is so little engine braking from the IS250 engine that it's hardly worth it. I suppose anything to give the overworked brakes a helping hand is a good idea though.

I always drive in 'power' mode, not sure if it still does it in 'normal'.

[Tel]

From memory does not the change from Auto to Manual always select Auto-selected gear as I have never given this a thought but use this all the time on the Continent.

Tel

[dave1]

Hope that makes sense. Thinking in terms of the Roadcraft system used by advanced bodies and the police it's Speed then Gear.

So any answers? Does boshing it down a couple of gears (in exactly the way I've just said I shouldn't) to slow cause harm to the auto transmission then way it would in a manual (excluding clutch wear, obviously)?

It depends on what speed you are doing when you downshift. On my GS430 the manual encourages the use of "engine braking" and tells you the maximum speed at which each downshift should be done. Does the IS handbook/manual not give this information?

I also remember being told by a police driving instructor back in the late 60's that if you are driving correctly then your brakes should, except in emergency, generally only be required to come to a final stop since anticipation and gearchanges should be sufficient for most eventualities.

[Exiled]

I also remember being told by a police driving instructor back in the late 60's that if you are driving correctly then your brakes should, except in emergency, generally only be required to come to a final stop since anticipation and gearchanges should be sufficient for most eventualities.

Like you, that's what I was told back in the 1960's.

A couple of years ago though I opted to go on a Speed Awareness Course to avoid 3 points on my license, part of the course involves going out with an instructor who then comments on your driving. I was told I used the gears too much when slowing down, I explained that was the way I'd been instructed and was told that over the years opinions had changed.

I still drive that way if in a manual transmission, can't change the habits of a lifetime and also it doesn't feel comfortable stopping or slowing by only using the brakes. When driving the Lexus I find it easier to flick the lever over (going from auto to gear 4) than using the brake to slow down. Going from 50mph in auto gear 6 to gear 4 increases the revs from 1400 to 2400 if it is damaging the car I'll have to change.

[dave1]

I also remember being told by a police driving instructor back in the late 60's that if you are driving correctly then your brakes should, except in emergency, generally only be required to come to a final stop since anticipation and gearchanges should be sufficient for most eventualities.

Like you, that's what I was told back in the 1960's.

A couple of years ago though I opted to go on a Speed Awareness Course to avoid 3 points on my license, part of the course involves going out with an instructor who then comments on your driving. I was told I used the gears too much when slowing down, I explained that was the way I'd been instructed and was told that over the years opinions had changed.

I still drive that way if in a manual transmission, can't change the habits of a lifetime and also it doesn't feel comfortable stopping or slowing by only using the brakes. When driving the Lexus I find it easier to flick the lever over (going from auto to gear 4) than using the brake to slow down. Going from 50mph in auto gear 6 to gear 4 increases the revs from 1400 to 2400 if it is damaging the car I'll have to change.

If it was going to damage your car then I don't think that Lexus, as manufacturers, would suggest this method.

[Baldchap]

So actually, nobody knows for sure?

[m1pui]

If you're going to fast for the gear you change into then you'll be putting undue stress on the drivetrain. If you change to a gear correct for the speed, so there's some engine braking but you're not so high into the rev range that you have to change up the second you feather the accelerator, then it should surely cause no more stress than accelerating or normal driving.

If you're in too high a gear, the engine revs are low and you're coasting, then you've got little or no instant control over the vehicle. Also, it maybe letting the engine labour which, I'm LED to believe is bad for the engine itself.

[TigerFish]

So actually, nobody knows for sure?

As mentioned already, in the manual (in the "Starting and driving" section for the GS430) it tells you how to use the gearbox for engine braking and at what max speed each gear could be engaged. If it was going to damage the car, it wouldn't tell you how to do it. So in answer to your question, anybody that has read their manual will know for sure ;)

[Tango]

Does the 250 accept a change to a lower gearing if the speed is too high? Certainly the IS-F just beeps at you if you try it, and I recollect my IS250 SE-L auto was the same, so there's no chance of damaging the transmission because until you brake to a suitable speed the system just will not accept it. Changing up in the IS-F is similar, but my recollection with the IS250 is that it just brings in the rev limiter (without the verbal indication?).

[fjcfarrar]

Hey all.

I've got a question that's been niggling me for a while.

In a manual, the adage 'brakes to slow, gears to go' is justified, because banging the car down a couple of gears with the sole purpose of slowing down puts a fair bit of strain on the drivetrain and wears the clutch prematurely...

Now, in my automatic IS250 I've got the 'manual' option on the paddles and stick (or at least manual selection of the highest gear it'll go into) which is fantastically useful for holding speed on slopes and general boy-racery if I'm in that sort of mood.

My question is, as I'm trolling up to a steep downhill, if I simply bang the stick across from full-auto to paddle-icious and select 3rd, say, will this process harm my transmission in the same way it could a conventional manual? There's no physical connection and the TC clearly allows slip in the non-driven direction or overrun wouldn't happen, but there is quite clearly a difference in the drivetrain between ratios or there'd be no engine braking.

What's the answer? Brakes then gears as per IPSGA (as you would/should in a conventional manual), or just bash it down without a care?

I was originally taught to use the gears to slow down and the brakes to stop. But back then cars had drum brakes - and usually ones that were really too small and/or badly designed (Ford). These would fade to useless after any real braking or going down steep slopes etc. This meant it was actually absolutely essential to use the gears/engine to do the bulk of slowing down etc. or you just could not stop. Since then, brake design and materials have improved beyond all recognition and you usually have to try really hard to make them seriously fade; so I don't think it is any longer necessary or even a good idea to use the gears to slow down - particularly with an auto.

If you don't believe me, find your favourite long steep slope, and when the road is clear and quiet, drive down it using just the brakes to control your speed, letting the auto do its own thing. When you get to the bottom give it some speed, then brake hard to see if the brakes work as usual. They will.

Yes, it can take a while to get out of old habits or adapt to progress - but it did when 5 or 6 gears came along.

Remember: Doing things for a reason is good; but doing them after the reason has gone isn't.

[dave1]

I was originally taught to use the gears to slow down and the brakes to stop. But back then cars had drum brakes - and usually ones that were really too small and/or badly designed (Ford). These would fade to useless after any real braking or going down steep slopes etc. This meant it was actually absolutely essential to use the gears/engine to do the bulk of slowing down etc. or you just could not stop. Since then, brake design and materials have improved beyond all recognition and you usually have to try really hard to make them seriously fade; so I don't think it is any longer necessary or even a good idea to use the gears to slow down - particularly with an auto.

If you don't believe me, find your favourite long steep slope, and when the road is clear and quiet, drive down it using just the brakes to control your speed, letting the auto do its own thing. When you get to the bottom give it some speed, then brake hard to see if the brakes work as usual. They will.

Yes, it can take a while to get out of old habits or adapt to progress - but it did when 5 or 6 gears came along.

Remember: Doing things for a reason is good; but doing them after the reason has gone isn't.

I don't see how the reason has gone, particularly since the Lexus handbook (for the GS 430 anyway) encourages the use of engine braking as I stated earlier and Rick (Tigerfish) has confirmed. Would Lexus really give this information if it was bad practice? Whether a car is manual or auto this practice is efficient use of the engine/gearbox and also gives more control.

[Baldchap]

There's a big difference between engine braking as a product of being in the right gear at the right time and changing gear solely with the sole intention of slowing down.

[TigerFish]

There's a big difference between engine braking as a product of being in the right gear at the right time and changing gear solely with the sole intention of slowing down.

Somehow I think you have made your mind up regardless of what is being said. You wanted to know if it damaged the car, it doesn't. Your call if you want to do it or not.

I'd sooner have my brake lights on because I am slowing or stopping, rather than because I have my foot parked on the brake to coast down a hill at a desired speed. That way I reduce the chance of someone arse ending my car because they can't actually tell what I am doing. All personal preference in the end I guess.

[Baldchap]

Somehow I think you have made your mind up regardless of what is being said. You wanted to know if it damaged the car, it doesn't. Your call if you want to do it or not.

I'd sooner have my brake lights on because I am slowing or stopping, rather than because I have my foot parked on the brake to coast down a hill at a desired speed. That way I reduce the chance of someone arse ending my car because they can't actually tell what I am doing. All personal preference in the end I guess.

You misunderstand completely - I am largely in agreement with both you and the last couple of posters beforehand.

The point of this post was that I actually wanted the specifics of what was happening to and with the TC on overrun/engine braking. The art of good driving is largely the same regardless of manual or auto - reduce speed then change gear. That's why ideally you'd have two hands on the wheel under braking - not only do you get more control in the event of problems, but it reduces BGOL which can result in destabilisation of the vehicle and is generally considered to be poor form (though in reality, most of us do it even in a manual, obviously moreso in an auto where it's unavoidable).

[fjcfarrar]

I was originally taught to use the gears to slow down and the brakes to stop. But back then cars had drum brakes - and usually ones that were really too small and/or badly designed (Ford). These would fade to useless after any real braking or going down steep slopes etc. This meant it was actually absolutely essential to use the gears/engine to do the bulk of slowing down etc. or you just could not stop. Since then, brake design and materials have improved beyond all recognition and you usually have to try really hard to make them seriously fade; so I don't think it is any longer necessary or even a good idea to use the gears to slow down - particularly with an auto.

If you don't believe me, find your favourite long steep slope, and when the road is clear and quiet, drive down it using just the brakes to control your speed, letting the auto do its own thing. When you get to the bottom give it some speed, then brake hard to see if the brakes work as usual. They will.

Yes, it can take a while to get out of old habits or adapt to progress - but it did when 5 or 6 gears came along.

Remember: Doing things for a reason is good; but doing them after the reason has gone isn't.

I don't see how the reason has gone, particularly since the Lexus handbook (for the GS 430 anyway) encourages the use of engine braking as I stated earlier and Rick (Tigerfish) has confirmed. Would Lexus really give this information if it was bad practice? Whether a car is manual or auto this practice is efficient use of the engine/gearbox and also gives more control.

A lot of the development and massive improvements in car brakes came about when Auto gearboxes first became popular. Most of these happily changed to the highest ratio going down any sort of a hill with only ineffectual ratio limiters to help - which few users knew how to use. Most recent autos provide a reasonable amount of engine breaking which can help without any action by the driver, but reliance can genuinely be placed on brakes now good enough to stop a runaway building. With manual cars, just driving in the gear appropriate to the speed you are travelling is all that is needed without dropping to a ratio that has the engine revving its nuts off.

Nevertheless, I think it is good to have in the background an alternative technique to slow down and stop should the brakes fail as all mechanical devices can - but not to drive as though they already have.

We are all different though - years ago most people used to fit horrible seat covers to protect car seats from becoming knackered; but I only ever used them when the seats were knackered. It took me years to get out of the habit of double-declutching from when all my cars had worn out synchromesh and admit I still rather miss the lovely exhaust sound when you did it.

[steve2006]

Modern transmissions are designed to ensure that a selected downshifted gear cannot be engaged if the road speed is too high to avoid damage to the transmission itself and over revving the engine above its normal rev limits.

You may find you are able to select the lower gear but it will not actually engage until the speed is within set parameters.

In my vehicle handbook it says

"Shift into the 2 position. The transmission will downshift to the 2nd gear when the vehicle speed is or becomes lower than 121 km/h (75 mph) and more engine braking will be obtained"

The same is said regarding a shift to L position but this will only engage when the vehicle speed is at or below 67 km/h (42 mph)where maximum engine braking will be applied.

The book also states to keep an eye on the rev counter to ensure it doesn't hit the red area.

I conclude from this that using engine braking will not cause unnecessary stress to the engine or transmission if the above guidelines are followed.

Similar maximum downshift speeds should apply to 5-8 speed transmissions and should be shown in your handbook,not sure how this works with the CVTs in the LS600 or CT200.

[Desmond]

There's a big difference between engine braking as a product of being in the right gear at the right time and changing gear solely with the sole intention of slowing down.

I was looking for an answer to this little matter and found this thread already going. Some fascinating reading but I think Baldchap has hit the nail on the head with this comment.

It always was taught that you should keep your engine speed at a level where it would be useful - that is, so you could pull away with no strain and slow down with reasonable revs. It wasn't really to save the brakes, it was to give you the best control over the car. This is why I think the current thinking about using brakes only to slow down is not only wrong, in some cases it can be downright dangerous. Coming down a hill or even up to a junction on the flat, you do not know what the road surface is like until you get there. In the winter you will see young drivers especially sliding up to junctions simply because they only used the brakes, have no grip, and the engine has been left to do its own thing.

As long as the IS250 does use engine braking then OK, but I do wonder if it uses it enough to maintain the right engine speed relative to the road speed. It seems to me to be engineered to coast a long way, maybe for fuel saving. So it might well be safest on steep hills and wintery roads to used manual control.