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What The Pan Man said.
Burger
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This is a joke right? No one answering the actual point in question and just stating the glaringly obvious...
1. Brakes are for slowing. Accepted.
2. Brakes cost less than gear boxes. Accepted.
Someone though, please answer the actual question (not one you made up)...
Why is it bad for an auto box to select a lower gear to hold a constant speed on a hill descent? And, if it is bad, then why does your box do this automatically?
Thanks, I live in hope
1. Brakes are for slowing. Accepted.
2. Brakes cost less than gear boxes. Accepted.
Someone though, please answer the actual question (not one you made up)...
Why is it bad for an auto box to select a lower gear to hold a constant speed on a hill descent? And, if it is bad, then why does your box do this automatically?
Thanks, I live in hope
The original discussion was about general use of engine braking
But in general driving, as mentioned you should use the brakes to slow down (e.g. for a corner) rather than down-shift and allow engine braking to slow the car. Apart from anything else, with a RWD car engine braking will act on the rear wheels only, which is not ideal.
A sustained hill descent is a different matter - constant brake application would give a significant risk of overheating and fade, hence the use of a lower gear to maintain speed.
But in general driving, as mentioned you should use the brakes to slow down (e.g. for a corner) rather than down-shift and allow engine braking to slow the car. Apart from anything else, with a RWD car engine braking will act on the rear wheels only, which is not ideal.
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Burger
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Fair point. I was taking the lead from the OP's point at post 5...
This is where Olly suggested it was bad for the gearbox. Perhaps he was answering the first post
I've driven autos for the last 20 years at least, with some manual cars for fun along the way, and I've always used engine braking at the appropriate times. To the best of my knowledge I've yet to damage an auto box so I think I'll stick with it and my advice to the OP is that yes, absolutely, it's perfectly fine to use a low gear to hold a constant speed on a descent. Use the brakes to get to the speed you want and a gear to hold it.
Regards,
Bellow
Hardcore MB Enthusiast
This is a joke right? No one answering the actual point in question and just stating the glaringly obvious...
1. Brakes are for slowing. Accepted.
2. Brakes cost less than gear boxes. Accepted.
Someone though, please answer the actual question (not one you made up)...
Why is it bad for an auto box to select a lower gear to hold a constant speed on a hill descent? And, if it is bad, then why does your box do this automatically?
Thanks, I live in hope
There was a huge discussion about this back in April or May, or thereabouts.
The OPs original point is being answered but is really about the fact that the auto doesn't sling it down a gear the same as he would himself, so the brakes take up the slack and combined with an autos reduced engine braking leads to greater wear of the brakes.
Manual boxes are A) tougher being all steel, B) load the gear faces and bearing tracks in the opposite sense under deceleration compared to acceleration thus spreading the wear. The most stressed component becomes the clutch plate unless a deftly timed double de-clutch with a blip is performed everytime.
By contrast, the most vulnerable of components in an auto are the friction linings which see stress under deceleration and acceleration and will wear prematurely when asked to perform braking duties. Bear in mind that the ECU will curb engine power on an upshift but nothing suspends decelerative inertia so the box sees the full force of a downshift.
As for the rights and wrongs regarding good driving practise - can of worms that one!
The handbook for most autos will tell you to shift down for a sustained hill descent (if the gearbox software doesn't do this automatically), presumably because some short-term extra wear on the powertrain is preferable to setting the brakes alight 
E.g. (from my Vito's handbook)
It also makes the point that down-shifting on a slippery road surface may cause the rear wheels to lose grip, with the potential for a skid.
E.g. (from my Vito's handbook)
It also makes the point that down-shifting on a slippery road surface may cause the rear wheels to lose grip, with the potential for a skid.
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Dryce
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So I apply the unpatented 'Dryce Guillotine' to such discussion.
In the UK we don't have much in the way of continuous steep inclines and declines. Not many places where there are warnings to use low gear on a descent and these usually aren't very long or sustained. The main concern isn't your engine or gearbox or brakes but safe speed on approach to the hazard and pretty much hang everything else.
Most of our cars are autos and have ABS and ESP.
I let the car do its thing. It seems to get it right.
IMHO, feel free to use your car/brakes/gearbox as you see fit - Olly was only offering advice and it doesn't take too much thought to understand that additional stresses placed upon a gearbox are likely to reduce it's eventual life.
Nothing wrong with more spirited driving at times, as long as you apply some mechanical sympathy and have an understanding of what is happening. But for routine driving, I definately prefer placing less strain upon the gearbox and focussing more on brakes to shave off excess speed
Will
Nothing wrong with more spirited driving at times, as long as you apply some mechanical sympathy and have an understanding of what is happening. But for routine driving, I definately prefer placing less strain upon the gearbox and focussing more on brakes to shave off excess speed
Will
Horrgakx
Active Member
Interesting thread indeed .
I would agree that brakes in an automatic get some more use than in a manual - certainly when you are 'creeping' in slow traffic or in stop/go traffic you are using them to hold the car back much of the time .
As for use of lower gears descending hills , when I taught advanced driving the rule of thumb always was that you go down a hill in the same gear you would use to climb it ( assuming a 'proper' hill and not a mild gradient of less than 100 yds ) - the comment about following drivers not knowing what you are doing strikes me as wrong : if you are descending a hill in an intermediate gear and need to slow further or even stop , following drivers will see your brake lights come on and be able to react ; on the other hand if you are braking all the way down said hill then need to brake harder or stop then following drivers will get no warning of this as brake lights were already on ! In some cases 3rd gear ( or Slope ) plus light brakes might be called for as 2nd would only be used in extreme circumstances such as descending a mountain pass with a trailer on the back .
While I would agree that dropping an autobox from D to S or 3 depending on how it is marked ( remember the S on the quadrant stands for Slope ) while on the overrun would cause an unpleasant jolt as the engine revs are forced to match roadspeed via the transmission , causing wear to brake bands etc , there is no more wear to the gearbox in an intermediate gear than in top once the gear is selected and revs matched .
Unless you have one of those new-fangled electronic boxes , you can bring in a part-throttle downshift either on the approach to a bend or prior to commencing a descent simply by applying a little throttle as you start to brake , then locking out the higher gear once the intermediate gear has engaged smoothly - this allows for safer and smoother progress in many situations but most especially when making fast progress on bendy roads , especially when conditions are wet . Although overlapping of braking and gear changing used to be forbidden , it is now taught by the police colleges . The last thing anyone wants is a gearchange mid-bend .
Neither the laws of physics , nor the basic principles of Position , Speed , Gear followed by the correct degree of acceleration to negotiate a hazard have changed as far as I am aware .
If you think such matters are critical in a car - they assume even greater importance when trying to get twenty-odd tons of Fire Appliance somewhere in a hurry .
I would agree that brakes in an automatic get some more use than in a manual - certainly when you are 'creeping' in slow traffic or in stop/go traffic you are using them to hold the car back much of the time .
As for use of lower gears descending hills , when I taught advanced driving the rule of thumb always was that you go down a hill in the same gear you would use to climb it ( assuming a 'proper' hill and not a mild gradient of less than 100 yds ) - the comment about following drivers not knowing what you are doing strikes me as wrong : if you are descending a hill in an intermediate gear and need to slow further or even stop , following drivers will see your brake lights come on and be able to react ; on the other hand if you are braking all the way down said hill then need to brake harder or stop then following drivers will get no warning of this as brake lights were already on ! In some cases 3rd gear ( or Slope ) plus light brakes might be called for as 2nd would only be used in extreme circumstances such as descending a mountain pass with a trailer on the back .
While I would agree that dropping an autobox from D to S or 3 depending on how it is marked ( remember the S on the quadrant stands for Slope ) while on the overrun would cause an unpleasant jolt as the engine revs are forced to match roadspeed via the transmission , causing wear to brake bands etc , there is no more wear to the gearbox in an intermediate gear than in top once the gear is selected and revs matched .
Unless you have one of those new-fangled electronic boxes , you can bring in a part-throttle downshift either on the approach to a bend or prior to commencing a descent simply by applying a little throttle as you start to brake , then locking out the higher gear once the intermediate gear has engaged smoothly - this allows for safer and smoother progress in many situations but most especially when making fast progress on bendy roads , especially when conditions are wet . Although overlapping of braking and gear changing used to be forbidden , it is now taught by the police colleges . The last thing anyone wants is a gearchange mid-bend .
Neither the laws of physics , nor the basic principles of Position , Speed , Gear followed by the correct degree of acceleration to negotiate a hazard have changed as far as I am aware .
If you think such matters are critical in a car - they assume even greater importance when trying to get twenty-odd tons of Fire Appliance somewhere in a hurry .
We do here in the Lake District
We have a few such places in the Highlands , too .
Dryce
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Not many and they're not actually that high or sustained.
Our geography in the UK isn't that extreme in terms of hills and mountains.
Bellow
Hardcore MB Enthusiast
Transmission Technology International - September 2010
Page 30, paragraph 4 for what gradient does for an auto box.
Page 30, paragraph 4 for what gradient does for an auto box.
Bellow
Hardcore MB Enthusiast
Beg to differ, living in Scotland as I do.
There are descents long and steep enough to make early engine braking a safeguard worth employing. And with some caution with RWD as it is all too easy to find the tight bend at the foot to be covered in sand from gritting or from being more generally washed down by the rain. With FWD it can be severe enough to lock the fronts stalling the engine and losing PAS, so disengaging the drive in either case has to be anticipated.
On such roads early use of engine braking is a safety requirement. Better some transmission wear than upside down on my roof!
