Engine braking - OK or not OK? (2 Viewers)

[roxburd]

Hi all,

Do you use engine braking in your motorhome? I find myself using it a little from time to time and I suspect it's frowned upon by HGV instructors... but I've never had any instruction so I'm curious. I'd never driven a big diesel before last month. I've done the IAM motorcycle advanced test and they have a saying - brakes to slow, gears to go. It basically means that you shouldn't use engine braking. They also advise block-changing - changing to the gear you want all in one go, rather than changing one gear at a time and declutching between. And not changing gear at all until you've finished braking. It all depends on circumstance but they are general guidance points.

I try to drive my MH at a very leisurely pace - but I'm still occasionally tempted to use a little engine braking - for example, as I'm entering a roundabout with a little more speed than I'd like to carry round and the gear I want will give some braking.

I realise this might seem a bit 'who cares' to some but I've found myself wondering and so thought I'd see what people think... I suppose the important question is this: can gentle engine braking cause any mechanical issues?? I wouldn't have thought so...

Cheers
(let the disagreements commence)

 

[poppycamper]

Just to add some numbers to it, a 3000kg motorhome descending 500 metres needs to lose energy. The amount of energy is 3000 x 9.81 x 500 = 14,715,000 joules, or 14715000 / 3600 = 4087.5 Wh.

If that descent takes 15 minutes, the average power dissipated by the engine/brakes is 4087.5 x 4 = 16,350W, ie 16.35kW. So imagine your brakes being heated by four 4kW heaters. That's why they get hot.

On the other hand, wouldn't it be nice if all that lovely energy could go into charging your batteries.

Quite right...exactly what I thought..

 

[Insider]

My PVC is based on a 2016 Fiat Ducato and it has a hill descent control button. Used it for the first time recently on the WAW on a pretty brtual pass and I was very impressed. It manages the braking via a combination of brakes and engine and allows you to speed up or slow down with the pedals but for the most part it's feet off and just steer.

 

[gilbaro]

Some interesting points raised here. I am new to motorhoming so I will base my comments on several different spheres of my driving over the years. I was a Police Traffic Officer for a while so had a Police Class One Certificate, I taught learners for a while but my main professional instructing experience was what is sometimes called advanced driving but more accurately called Driver Awareness Training. I was also an instructor trainer. I would describe DAT as trying to help high mileage, often not very receptive, business drivers stay alive. There were some differences in teaching methods. Police training and learner training whilst having obvious differences was very black and white whereas DAT had a more flexible approach. I think one of the the best statements I ever learnt and frequently passed on to others was "the only fixed rule in driving is no fixed rules" there can always be a reason to do something differently. I know so people will say what about traffic law. Well there are many defences to breaking traffic law but i will not go into that side now.
So back to braking. There are many techniques and most can be right in particular situations. Firstly why are we braking, it sounds a stupid question but is it because we need to slow down to stop or is it because we have got too close to the vehicle in front. The second reason usually results in a panic application of the brakes when our concentration returns. You will often see what I refer to as "the dabber" on the motorway. In some situations this can be the start of the chain reaction that leads to a motorway pile up. So here i would suggest more space and try to only use the brakes if you have really got to stop. Remember the biggest danger when you are braking is generally behind you!
So what happens when we brake? Weight transfers to the front of the vehicle which increases instability, large amounts of heat are created in the brakes, particularly the front brakes and very importantly the brake lights come on.
What happens if we change down. Potentially the vehicle is not so unstable but we risk transmission damage if we don't match the revs properly and very importantly we don't wake up the driver behind with the brake lights. Remember we only concentrate about 25% of the time when driving!
So what are the solutions. Firstly manage your space so that heavy braking is less likely. Generally I will try to brake to the speed that I can deal with a particular situation and then select the appropriate gear for that speed so that could involve a block change but not always - it depends on the situation.
What about hills. As suggested if you brake all the way down a long hill you will likely have problems. Your brakes will overheat and dissipate so much heat that they will glaze and in extreme situations catch fire. It is also likely that the brake fluid will boil. My suggestion would be brake to a speed lower than you need initially and select a low gear (appropriate to this speed) and if necessary repeat this process further down the hill. Bear in mind that your brakes will remain hot for quite a time afterwards so maintain extra space once on the flat.
Try not to brake in bends if possible, if you can corner under a gentle amount of power, maintaining your entry speed, this will maximise stability whereas braking in the bend will cause a heavy loading of the outside front wheel and potentially catastrophic instability.
Remember that braking, steering and acceleration all use a proportion of the available grip so if you are using 100% of your grip for braking there is nothing left for steering which in turn means you are skidding.
It is easy to say maintain space and brake early but we are only human so driving is always a compromise. If you are distracted by phone, satnav, passengers, scenery etc. try to create more space around the vehicle. This in turn will give you more time to react slower.
Sorry if I have sent you to sleep with my epistle but hopefully it has provoked thought.

 

[chaser]

I have used engine braking for 60 years and believe it or not I have never had a new clutch in a motor vehicle, had plenty in tractors but never a passenger vehicle.

^{_{Subscribers  do not see these advertisements}}

 

[Chrisvh]

Some interesting points raised here. I am new to motorhoming so I will base my comments on several different spheres of my driving over the years. I was a Police Traffic Officer for a while so had a Police Class One Certificate, I taught learners for a while but my main professional instructing experience was what is sometimes called advanced driving but more accurately called Driver Awareness Training. I was also an instructor trainer. I would describe DAT as trying to help high mileage, often not very receptive, business drivers stay alive. There were some differences in teaching methods. Police training and learner training whilst having obvious differences was very black and white whereas DAT had a more flexible approach. I think one of the the best statements I ever learnt and frequently passed on to others was "the only fixed rule in driving is no fixed rules" there can always be a reason to do something differently. I know so people will say what about traffic law. Well there are many defences to breaking traffic law but i will not go into that side now.
So back to braking. There are many techniques and most can be right in particular situations. Firstly why are we braking, it sounds a stupid question but is it because we need to slow down to stop or is it because we have got too close to the vehicle in front. The second reason usually results in a panic application of the brakes when our concentration returns. You will often see what I refer to as "the dabber" on the motorway. In some situations this can be the start of the chain reaction that leads to a motorway pile up. So here i would suggest more space and try to only use the brakes if you have really got to stop. Remember the biggest danger when you are braking is generally behind you!
So what happens when we brake? Weight transfers to the front of the vehicle which increases instability, large amounts of heat are created in the brakes, particularly the front brakes and very importantly the brake lights come on.
What happens if we change down. Potentially the vehicle is not so unstable but we risk transmission damage if we don't match the revs properly and very importantly we don't wake up the driver behind with the brake lights. Remember we only concentrate about 25% of the time when driving!
So what are the solutions. Firstly manage your space so that heavy braking is less likely. Generally I will try to brake to the speed that I can deal with a particular situation and then select the appropriate gear for that speed so that could involve a block change but not always - it depends on the situation.
What about hills. As suggested if you brake all the way down a long hill you will likely have problems. Your brakes will overheat and dissipate so much heat that they will glaze and in extreme situations catch fire. It is also likely that the brake fluid will boil. My suggestion would be brake to a speed lower than you need initially and select a low gear (appropriate to this speed) and if necessary repeat this process further down the hill. Bear in mind that your brakes will remain hot for quite a time afterwards so maintain extra space once on the flat.
Try not to brake in bends if possible, if you can corner under a gentle amount of power, maintaining your entry speed, this will maximise stability whereas braking in the bend will cause a heavy loading of the outside front wheel and potentially catastrophic instability.
Remember that braking, steering and acceleration all use a proportion of the available grip so if you are using 100% of your grip for braking there is nothing left for steering which in turn means you are skidding.
It is easy to say maintain space and brake early but we are only human so driving is always a compromise. If you are distracted by phone, satnav, passengers, scenery etc. try to create more space around the vehicle. This in turn will give you more time to react slower.
Sorry if I have sent you to sleep with my epistle but hopefully it has provoked thought.

Great post! I was a Class 1 Advanced Driver, car and motorcycle for many years. Still with IAM. You have nailed the salient points. Phrase I always use from Roadcraft is “car sympathy”. Applies to bikes as well. Making smooth, controlled progress should always be the aim.

 

[LostInSpace]

Recently made the change from manual to 9 speed auto which utilises engine braking in situations where I’d habitually use the brakes.

Yes, I am still learning about it, but I have noticed it changing down when going downhill.

 

[bladerunner]

Totally agree with comments above.
I think the concern is that you don't use the clutch to brake. i.e. don't slam into a low gear at high speed and then slip the clutch to slow.
Aș per above, my Boxer RT can be ridden on most A roads in 3rd-4th gear (many new riders use too high a gear) and then slow to corner by rolling off the throttle, back on as you exit. You can ride miles without ever touching the brakes - it's much more enjoyable.
On motorways if you judge distances and look far ahead, again very little braking.

On steep mountains in my 5.5t MH I may be down to 3rd or 4th gear - or even 2nd (out of 7), but slow first and then override to manual.

 

[WESTY66]

Always use the engine to slow down, be it bikes cars or 5ton moho, Even the comfortmatic anticipates you going downhill and drops the gears
Do wish I had an exhaust brake tho, a Jake brake would be awesome

 

[poppycamper]

I think the concern is that you don't use the clutch to brake

I think the concern is that you don't use the clutch to brake

Absolutely.. clutch to change gear, when and only when you have used brakes, or natural deacceleration (lifting off the go pedal) to match engine speed to road speed and if you get it right you should be able to change gear easily... and if experienced enough without pressing clutch...

^{_{Subscribers  do not see these advertisements}}

 

[WallaceandGromit]

When I had a wobby box, always used engine braking even when I drove Range Rovers I'd shift to command shift, so I could use the gears do the same in the MH

 

[jerryz]

Engine braking is a useful aid and tool its a fundamental driving skill , on Bikes, Cars and heavy vehicles ,,,,mind u some modern petrol engines in certain Motorcycles and cars have engine braking tuned out and that makes them , unpleasant to ride for me and also potentially dangerous as they then only rely on brakes

 

[rod_vw]

gilbaro I like your comment about 'brake dabbers' but unfortunately with modern adaptive cruise control (ACC), even when set for maximum distance between vehicles, the brake lights come on when the ACC is active and the system needs to slow just a bit.
In 'manual' driving the driver would decelerate in the space in front without braking and use his eyes brain to moderate both speed and distance between vehicles.

To me it's this flashing of brake lights that causes many other drivers to brake unnecessarily and potentially cause trouble behind.

Yes I have two vehicles with ACC and I use it, my other vehicle, a 1946 VW Beetle, needs an egg timer to initiate both accelerating and braking!

 

[roxburd]

Well, that's a pretty clear consensus - at least on long declines, it's essential to use engine braking to take some of the load off the brakes! I guess it was once even more essential when braking systems weren't as powerful as they are today. Living in Suffolk and only getting the MH two weeks ago, it's not something I've encountered in a big diesel yet!

I must admit, the IAM saying 'gears are for going and brakes are for slowing' does sound entirely inconsistent with another of their recommended practices - Acceleration Sense. As Guigsy says, this is when you plan ahead so well that you can do all your deceleration by closing the throttle rather than braking. I think the difference is a matter of balance - the ideas is that you shouldn't be decelerating hard by engine braking alone - stomping down early through all the gears with the engine screaming at high revs - when braking would be more effective and shows more 'mechanical sympathy' for the machine. And as Guigsy again says, applying the brakes also illuminates the brake lights, providing an essential warning to following drivers.

So I guess it's all about balance, then. I do understand your points, Dazzola ... but when I'm riding like that I know I won't be getting anywhere near a pass in the AIM test... the ACU test, yes, the IAM - no. I've watched truck cab racing at Brands Hatch and I don't fancy putting my MH through that

I had to replace the clutch on my CBX550 Honda motorcycle in the 80s - a very under-appreciated machine. I don't know if it was accelerating or my engine braking that wore that out but I realised there was a problem under hard acceleration in the power band when I hit a bump in the road and it would start slipping, losing all power. First time it happened I was trying to get past an artic with traffic coming the other way - scary. I did rag that machine. But it loved it

Well, I'm gonna aim to drive the MH like Wee Bold Davy - maximum mechanical sympathy and accident free! If I can get half way there I'll be happy.

Cheers all.

 

[rod_vw]

I don't understand why a clutch should take any strain when changing down, surely it's normal to blip the throttle in the neutral phase to bring the engine revs up to match the new gear ratio input shaft / clutch plate speed.
As the owner of a vehicle without synchromesh on any gear I know that not doing that will smash the gearbox!

I guess modern drivers are not aware of any such actions, they just expect the mechanical parts to take the strain!

If drivers had a basic grasp of vehicle mechanics they would be much better drivers, my wife will agree on that.

^{_{Subscribers  do not see these advertisements}}

 

[TheCaller]

I think I can see a few reasons why 'engine' braking might be discouraged. Leave aside the hill descent, where is it an essential component of good vehicle control.

In a manual box, every time you change gear, there is wear in the release bearing. I rather doubt that new drivers are being taught to match engine speed to road speed before letting the clutch re-engage, so also causing clutch plate wear. So what is being discouraged might better be described as 'clutch' braking. Also bear in mind that brakes are much more efficient than they were when most of us started driving.

So with the relative cost of replacing disc pads to hauling engine/gearbox out & apart to fix a clutch, you can see that wearing out brake pads rather than the clutch mechanism is a better option.

An experienced driver with a degree of mechanical knowledge & sympathy will use engine braking where appropriate, but will also use brakes & block change gears downwards where appropriate. There is no comparison between a modern vehicle with maybe six gears & good brakes & a new vehicle on the road 60 years ago with maybe only 3 gears & dreadful brakes.

Anyway, for a motorhome, surely the more relevant question is - why aren't we all driving automatics?

 

[Burgo]

the IAM motorcycle advanced test and they have a saying - brakes to slow, gears to go. It basically means that you shouldn't use engine braking. They also advise block-changing - changing to the gear you want all in one go, rather than changing one gear at a time and declutching between. And not changing gear at all until you've finished braking.

What??!
That's pretty well the exact opposite of what I was taught in 1970 and has kept me good ever since. Surely you should be anticipating the gear required in advance and being in it and using the throttle to be at the right speed at any point? Brakes only as you stop most of the time - apart from emergency stops.

 

[Figaro]

Anyway, for a motorhome, surely the more relevant question is - why aren't we all driving automatics?

probably because we don't want to risk joining the comfortmatic failure club

 

[VXman]

I remember being on a coach many years ago that had some kind of electric retarder. I guess a magnetic retard system like this. Anyone got similar on their motorhome????

Electromagnetic Braking Systems - Telma S.A.S.

Design for Electromagnetic Retarders for Industrial Vehicles and Industrial Applications. World Leader Braking Induction.

www.telma.com

 

[jezport]

Signs on dangerous hill decent usually say "engage low gear"

^{_{Subscribers  do not see these advertisements}}

 

[funflair]

I remember being on a coach many years ago that had some kind of electric retarder. I guess a magnetic retard system like this. Anyone got similar on their motorhome????

Electromagnetic Braking Systems - Telma S.A.S.

Design for Electromagnetic Retarders for Industrial Vehicles and Industrial Applications. World Leader Braking Induction.

www.telma.com

I remembered the Telma from my school bus days also so when I got the chance to have one on a motorhome I jumped at it, brilliant bit of kit that automatically backs up the foot brake when applied, or can be applied on it's own to gently maintain a given speed downhill, as the Telma is fitted in the propshaft it is only possible on rear wheel drive or four wheel drive chassis, I know that these are available on IVECO daily based motorhomes but not sure if it is an option on RWD Sprinter or Crafter, they are heavy though

 

[roxburd]

I remembered the Telma from my school bus days also so when I got the chance to have one on a motorhome I jumped at it, brilliant bit of kit that automatically backs up the foot brake when applied, or can be applied on it's own to gently maintain a given speed downhill, as the Telma is fitted in the propshaft it is only possible on rear wheel drive or four wheel drive chassis, I know that these are available on IVECO daily based motorhomes but not sure if it is an option on RWD Sprinter or Crafter, they are heavy though

Is it friction-based (brake pads/shoes) or induction-based (magnetic)?? Very interesting!!

 

[funflair]

Is it friction-based (brake pads/shoes) or induction-based (magnetic)?? Very interesting!!

No it's not friction based so no maintenance requirements, it works purely electromagnetically as per the web link at post #78.

 

[Figaro]

I know that these are available on IVECO daily based motorhomes but not sure if it is an option on RWD Sprinter or Crafter

Project Amber had a Telmar on his MB sprinter ex ambulance

 

[jdk62]

What are people’s thoughts on the “hill descent” function on some Moho’s?

^{_{Subscribers  do not see these advertisements}}

 

[tacr2man]

Endurance brake systems are required on dangerous goods vehicles to save extensive use of service brakes

 

[TerryL]

As a coach driver we were forever getting slated by the mechanics as they were always dealing with "glazed" brake pads, due to the very light braking methods we used to provide a smooth ride for our passengers. Using the gearbox was usually not an option as most coaches were auto so we learned to drive using anticipation - the Telmar (if you had one) was only used in long downhills to restrict the speed. You didn't last long if you were a "two pedal" driver, either full throttle or full braking!

For me, although I was taught from the age of 15 (!) to be sympathetic mechanically anyway, it means I plan ahead and use the throttle to give me correct speeds, only braking to finally get down to the speed I needed if I'd mis-judged it before block-changing to the next gear required. If I'm using clutch braking (changing down and reengaging the clutch to slow down) I've not been paying enough attention! Don't get me wrong, I like to "make progress" just as much as the boy-racers but I do it with sympathy for the vehicle and my passengers. In 60 years of driving I've never had to have a clutch plate replaced on any vehicle due to wear. Had a few brake pad changes though!

Very recently had the clutch changed when the slave cylinder failed (gearbox out job on the Ducato) and the fitter told me there were thousands of miles left on the drive plate, it was simply a no-brainer to change it whilst the box was out. And this on a model that was plagued by the dreaded gearbox shudder when it was first produced, remember them? I always said it was the driver, not the vehicle, although the design could have been better.