Engine Braking

[dave@york]

In the Q&A part of the 'Drive' section of the Sunday Times last Sunday, a reader had raised the subject of engine braking with auto transmission on gradients and also on long slowdowns such as a visible traffic stop half a mile ahead.

The magazine experts said that engine braking of this type should be avoided because it would rapidly wear out the gearbox, and that brake parts are much less expensive than a gearbox repair.

Having had auto trans for many years, I have always dropped down a gear or two to provide braking in these situations.

My new Avensis is a 6 speed auto, and has paddle flips on the steering wheel to make it easy to move down and up a gear. I have taken this as confirmation that what I have been doing is OK because whatever Toyota supports is kosher.

Any experts out there please>

[Cyker]

On some automatics they don't recommend engine braking so much (I think CVT and torque converters mainly but I may be wrong there?), but on manuals, semi-autos (like the Toyota MMT) and the HSD it is fine, will not cause any significant wear, will put less stress on the brakes and will save fuel (as the car stops sending fuel to the engine when engine braking).

The only way you could cause any damage engine-braking is slipping the clutch too much (In a manual) or dropping too many gears so the engine is over-revved.

[Druid Boy]

The police use the Information Position Speed Gear Acceleration system and that says to me that you sort out your speed before sorting out your gear not the other way around. Its ok to decelerate by lifting off the power and adjusting your gear as your speed decreases but shifting down early to make the speed decrease would not, in my opinion, be a good thing. *Debate begins*.....

[korat102]

I agree with the OP's opinion on this one. i.e. taking the opinions of motoring hacks with a pinch of salt...

The way I was taught (admittedly a long time ago...but we won't go there, thanks) was that you change down as you slow down so that you're always in the right gear. In an automatic that's not really an issue unless you're forcing it into a particular gear...the only reason I can see for doing that is if you're going down a long gradient that's going to cook your brakes or you're tying to pull away in snow and you want to force it into a higher gear to reduce wheelspin and those are the reasons they provide a manual option, aren't they?

I can't imagine the manufacturers going to the trouble of providing a means to allow gear selection and engine braking if it's going to damage the system, reliability is in their interests as well as ours.

[Whitewagon]

It is obviously true that brakes are much cheaper and simpler to replace than a gearbox or clutch. The experts rule on which gear to be in is that you should always be in the correct gear for the speed of the vehicle on the road. Clearly with an automatic/CVT box this is generally done for you. However if negotiating a steep incline then once you have braked to the correct speed you can then hold the car in a lower gear to try and maintain a safe speed, this shouldn't have any adverse effect of the auto box.

Better than using the gears to slow down is advanced observation coupled with acceleration sense to vary the speed of the vehicle for the unfolding circumstances that lie ahead, this will also reduce fuel consumption, wear on the transmission components and give you and your passengers a smoother ride.

Until very recently, at least, driving school instructors would teach their pupils to change down the the gears when slowing down for a junction or obstruction, this often entailed three or four gear changes before coming to a standstill, totally pointless and causes unnecessary wear on the transmission and loss of some control of the vehicle. Use the brakes to reduce the speed and then select the correct gear for the next manoeuvre before moving on, obviously this is again done for you in an auto box. In an auto box if you want to maintain a lower gear for quicker acceleration then use the manual or sport option to for this.

[dave@york]

Some very sensible viewpoints on this forum issue, but I'm still a bit puzzled.

My simple mind says that if I accelerate at say 0.2g then I'm not going to do any harm to my auto trans.

If I decelerate at 0.2g by using the steering wheel mounted paddle flaps which Toyota have provided, then the torque on my trans will be equal and opposite, and should do no harm either.

I have enormous faith in Toyota's engineering expertise (seriously they are top of the world premier league), and it seems that Toyota, by providing these paddles, are facilitating engine braking. However there is huge body of opinion amongst very knowledgeable drivers saying 'don't go there',

Help!

[Whitewagon]

Dave,

The advice/opinion you receive on here is generally given in good faith by people who, like you, have their own method of driving. I suspect that few, if any, have any expert engineering knowledge as to whether or not the way you drive is likely to cause damage or excessive wear on your transmission. As you say Toyota is unlikely to have fitted the paddle system if it was likely to cause damage, there is usually an override system with autos that would not allow you to change down at a speed that was too high for the gear you are attempting to engage but I have not tested this on my car nor do I intend doing so as it would be against my principles of safe driving and car sympathy.

My view is that engine braking in either a manual or auto box is fine providing it is done with car sympathy, what I mean by this is when you do change down you try to match the engine speed with the road speed as opposed to a sudden jolt caused by engaging the lower gear which, in my opinion, would not be conducive to reasonable care of the transmission. If you base your method of engine braking on this principal then I doubt you would cause any undue wear on your transmission.

Whatever you do should be based on the fact that you are in a position to have maximum safe control of your car (which is why I don't subscribe to the driving school method described above as every time you take your hand off the steering wheel to do something else you are not in maximum control) and the car remains in a stable state of balance on the road.

[dave@york]

Hello Whitewagon

I think your analysis is spot on.

In days of old when brake systems were not reliable it was common practice to double declutch and drop down a gear at what would now be considered inappropriate speeds.

With better and dual brake systems, the practice was regarded as an old duffers thing.

Nowadays we can stand back and make a sensible judgement on these things.

Your "car friendly" philosophy for dropping down gears is the one to go for I think.

There is a fuel saving to be made as one correspondent noted. Also a saving on brake wear and tear without a risk to the transmission system, if done in a "car friendly" way.

[frankie406]

I've been told not to engine brake because of dual mass flywheels in the manual box..its cheaper to replace pads than a clutch system.