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If you drive with mechanical sympathy re braking, you'll be amazed at how abusive of their vehicles (of all sizes) so many other drivers are.
Approach a junction steadily under engine/gear/foot braking with the intention of not actually stopping unless needed, ie by timing your approach to get the traffic light change or to enable a smooth merge onto a then clear roundabout...and you'll have numerous vehicles of all sizes charging past still accelerating right up to the very last moment then jamming the brakes on and invariably coming to a harsh stop, most drivers don't think they are driving aggressively it's become the norm.
Have a look at some front wheels, are they covered in thick baked on brake dust?, if so then chances are the driver, or some of the drivers if a fleet vehicle, drive on the brakes like this without thinking, most of them haven't a clue they are doing this and if you tried to explain making good use of terrain and maintaining progress you would be met by a blank expression.
Every yard you travel with your foot off the throttle is fuel free, and it has the added benefit of making your tyres and brakes last far far longer than the other method, quite apart from being a much more pleasant ride for passengers.
The other thing with keeping your foot on the brakes at the point they come to a halt after heating them up, is that small amounts of brake friction material are transferred onto the disc, i'm gentle on the brakes on all vehicles i drive, so now and again i'll give the car a couple of hard stops to de-glaze the discs, but when doing so i don't allow the vehicle to come a complete halt....if you braked hard from speed and held the brakes on for even a few seconds, then removed the pads, there would be imprints of the pads on the discs which would take several minutes using wet n dry to remove.
I, or rather some of my colleagues, have had a bit of eye opener with what these new vehicles record, my new lorry sends a report to the maker who in turn sends it to my boss every week, you would not believe the details in these reports, notable are sharp braking and harsh cornering but every aspect of your driving is being recorded and the exact place it's happening to within a couple of metres...same maker as the car in question in HJ's column.
Edited by gordonbennet on 14/07/2019 at 16:34
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Sounds like VERY poor punter relations to implement that level of monitoring for a private car.
I suppose they could keep it a secret though. i.e. IF its bad driving, produce the evidence to deny a warranty claim, otherwise, be mysteriously unable to access it.
As per those ünintended Toyota acceleration"" episodes a few years ago, IIRC.
Since i coast a lot, (because I'm wicked), I've thought of rigging some water cooling for mountain descents, but I'll probably never get around to it.
There's usually some brokeness that's a higher priority..
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Since i coast a lot, (because I'm wicked), I've thought of rigging some water cooling for mountain descents, but I'll probably never get around to it.
If your car has fuel injection rather than carburettor(s), if you roll down hill in gear with foot off the accelerator, the ECU shuts off the fuel completely.
If you coast in neutral, it will feed fuel to the engine to keep it running, so use more fuel..
If you coast with the engine off, you will exhaust the vacuum in the brake reservoir by braking and could find no brake assistance from the servo when you need it.
Your choice, of course.
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If your car has fuel injection rather than carburettor(s), if you roll down hill in gear with foot off the accelerator, the ECU shuts off the fuel completely.
If you coast in neutral, it will feed fuel to the engine to keep it running, so use more fuel.
I think this argument has been done to death here before, but however. Coasting in neutral with the engine off means engine braking drag is eliminated and is the method 'hyper-milers' use to obtain tremendous economy figures. As I once managed to obtain 90-odd MPG out of a Maxi on an unobserved economy run.
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Some carb equipped cars circa mid-eighties before the universal introduction of fuel injection had an idle circuit cut-off valve which operated on the overrun with a closed throttle and opened again at lower rpm - on a Volvo 360 GLS I had.
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If your car has fuel injection rather than carburettor(s), if you roll down hill in gear with foot off the accelerator, the ECU shuts off the fuel completely.
If you coast in neutral, it will feed fuel to the engine to keep it running, so use more fuel.
I think this argument has been done to death here before, but however. Coasting in neutral with the engine off means engine braking drag is eliminated and is the method 'hyper-milers' use to obtain tremendous economy figures. As I once managed to obtain 90-odd MPG out of a Maxi on an unobserved economy run.
Something I’ve noticed about my little 3 pot engine, when coasting downhill in gear behind other vehicles, I usually have to brake and quite a lot when they don’t. I assume they have far more drag in the drivetrain, presumably from the cylinders. It is an efficient little engine. The drag of course comes from various parts of the drivetrain. In my experience most fuel savings come from gradual acceleration, little or no braking, and using the optimum gear and speed. And driving on a hot summers day. Being in or out of gear makes little difference for the reason given earlier, though out of gear is unsafe.
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Since i coast a lot, (because I'm wicked), I've thought of rigging some water cooling for mountain descents, but I'll probably never get around to it.
If your car has fuel injection rather than carburettor(s), if you roll down hill in gear with foot off the accelerator, the ECU shuts off the fuel completely.
If you coast in neutral, it will feed fuel to the engine to keep it running, so use more fuel..
If you coast with the engine off, you will exhaust the vacuum in the brake reservoir by braking and could find no brake assistance from the servo when you need it.
Your choice, of course.
Carb. Only had one non-diesel fuel injected car.
I don't generally coast engine-off in brake-servo equipped cars either, though I find the extent to which servo-assistance is necessary varies quite a lot.
Was very popular with non-servo VW Beetles in Palestine, and quite competitive. Motor sport without the motor..
Have done it once or twice on my favorite long coast, down from the Rest-and-be-Thankfull Pass to Arrochar.
Silent, scary excitement
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<< I don't generally coast engine-off in brake-servo equipped cars either, though I find the extent to which servo-assistance is necessary varies quite a lot. Have done it once or twice on my favorite long coast, down from the Rest-and-be-Thankful Pass to Arrochar. >>
I would never 'coast engine-off' in any car, even back in the 1960s. Lack of brake servo is the obvious reason, but the steering lock needs to be considered, and in later days PAS too. But I recall travelling over 10 miles in neutral on a long steady descent somewhere in southern Utah, probably in 1966.
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Nice post GB. I admit I tend to keep my foot on the brakes for a few seconds, not realising it could cause problems.
You obviously know this already, but gentle braking and acceleration, and improved forward observation also reduce wear on the gearbox, the engine and the tyres as well as consuming less fuel.
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Reading the original letter, this just doesn't add up and there is no logic from the dealership. An Audi s5 is a performance machine and will be equipped with brakes to suit. 231c? That's nothing for a set of discs to reach! I've seen them actually glowing red hot on rally cars in the past, so my guess is this is a misdiagnosis and the real problem lies elsewhere, it could be Tyres, hubs, driveshafts any of which might be out of alignment. The fact that 3 sets later there is still a vibration is the big clue! I would try a different dealership,or ultimately a specialist decent independent.
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Would there be some sort of brake assist system fitted to an S5? Rather than the usual "blame the driver" reaction from the dealer, perhaps there is some sort of fault with the brake assist system? Or the brake caliper pistons are not fully releasing the pads causing the discs to overheat? After three sets of discs you would have thought the dealer would have suspected some fault other than a driver problem.
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I admit I tend to keep my foot on the brakes for a few seconds, not realising it could cause problems.
There must be something in this, but I can't help thinking it may be less than sometimes suggested. The running clearance between disc and pad is pretty tiny as there is little mechanical force to remove pad from disc, so ventilation will be almost nil with the vehicle stationary. Any difference in heat transfer must be due only to stronger conduction while the pedal is depressed.
It's always better to use the handbrake, if only to avoid dazzling the driver behind.
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I admit I tend to keep my foot on the brakes for a few seconds, not realising it could cause problems.
There must be something in this, but I can't help thinking it may be less than sometimes suggested. The running clearance between disc and pad is pretty tiny as there is little mechanical force to remove pad from disc, so ventilation will be almost nil with the vehicle stationary. Any difference in heat transfer must be due only to stronger conduction while the pedal is depressed.
It's always better to use the handbrake, if only to avoid dazzling the driver behind.
Brake caliper pistons should retract a few thousandths of an inch when the hydraulic pressure from the braking system is released. This is due to the action of the square-cut seals which deform under braking pressure and grip the pistons. When the pressure is released the seals revert to their original shape and drag the piston back a tiny amount.
I have just rebuilt a pair of motorcycle 4 piston calipers on my Yamaha and the pads now completely release the discs - testing them in the workshop it's just possible to see the pistons moving that tiny amount back into the calipers when the brake lever is released, because everything is nice and clean and bright and shiny!
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Brake caliper pistons should retract a few thousandths of an inch when the hydraulic pressure from the braking system is released. This is due to the action of the square-cut seals which deform under braking pressure and grip the pistons. When the pressure is released the seals revert to their original shape and drag the piston back a tiny amount.
Nothing to say the garage knows what its doing, wouldn't be the first to blame the driver for a fault on the car!
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I agree with the above advice and the retraction of the pistons. But the temperature quoted by the garage does actually not seem that exceptional.
A quick Google shows ~200C as being normal.
https://www.motorauthority.com/news/1109461_thermal-camera-shows-how-hot-brake-rotors-get-during-use
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These are my opinions only.
The vehicle is very new, and i suspect the driver has not allowed the brakes to bed in fully before subjecting them to hard treatment, until they are bedded in not all of the friction material area will be in uniform contact with the disc, this will create very hot spots where they are contacting, once warping of the disc has happened there is no fixing it other than refacing or replacing the disc, and if the same hard treatment before fully bedding happens again, the same results....100 miles of normal driving on normal roads should bed these new pads to the discs nicely.
It would be interesting to see the front wheels of this car after a typical week's driving, i suspect they will be caked in brake dust, i see this with my work vehicle where more brake dust on the front wheels can be created in my two days off than i can put on in 6 months, that is no exaggeration, it's confirmed by the reports the vehicle sends out, the vehicle itself also has friction material measuring on the dash menu.
Many drivers do not realise how hard they are driving, if they pulled up just after the last roundabout of say A43 Brackley by-pass section and touched the discs they would see what heat is being generated.
The recording equipment fitted to some especially higher range modern cars isn't exactly well publicised, many people appear to be content with total surveillance, so long as it's someone else unpopular being monitored and dealt with accordingly, makers are not going to be explaining all of this for obvious reasons, and it remains to be seen if the state forces makers(if they object at all?) to allow them access to this if they don't already have it with selective cases.
If i owned the car in question, first thing i would do is check for any brake binding, ie drive along a motorway or similar for a good distance without touching the brakes then stop at a convenient point without braking at all, it can be done easily with some forethought, then walk around the car feeling for any excess heat in the hubs/brakes...many vocational drivers practice this because such dragging will not be picked up at service times, it also helps diagnose early wheel bearing failure.
I would then drive the car more reasonably for at least 100 miles once fixed, and then if the problem persists, i would bin the undoubtedly hard OE pads and as an experiment stick a set of Brembos in the front and repeat the process and see what happens.
Cars do sometimes not have large enough brakes, not suggesting this is the case with this Audi and i doubt it has any relevance to this, Rover 827/Sterlings were a case in point, i bought an ex police driving school 827si many years ago, in the extensive police garage service history the car had received numerous sets of new front discs in its police time, probably every service so every few months, the car was an underrated flying machine of its time and warping of the front discs regularly continued during my ownership as well, a stop from 3 figure speeds would often mean a warped set of front discs as a result, the equivalent Honda had no such issues, though whether that was bigger brakes or a more gentle driving style due to the type of owner i don't know...i was younger and more shall we say enthusiastic in those days :-)
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Cars do sometimes not have large enough brakes, not suggesting this is the case with this Audi and i doubt it has any relevance to this, Rover 827/Sterlings were a case in point, i bought an ex police driving school 827si many years ago, in the extensive police garage service history the car had received numerous sets of new front discs in its police time, probably every service so every few months
Just goes to show you they never learn, the SD1 was the same. There was a Jag disc conversion that solved the problem for that car.
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Just goes to show you they never learn, the SD1 was the same. There was a Jag disc conversion that solved the problem for that car.
Never knew that, i wonder if the 827 had a similar fix.
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Live in a very hilly area. Lots of brake usage down hills. As it's an auto, I keep foot on brake at junctions etc..
Never had any heating issues - ever - in any car.in 35 years of living here.
Only issue was in Scotland 50 years ago driving a 1946 Rover 16. At the end of a 1 mile long descent in Highlands, brakes emitted clouds of smoke..And did not work (drums)
What am I doing wrong?
(Front pads last 30k miles)
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Just goes to show you they never learn, the SD1 was the same. There was a Jag disc conversion that solved the problem for that car.
Never knew that, i wonder if the 827 had a similar fix.
I had 2- 827s over a few years but the disc wear I put down to soft metal as the pads tore them up, over 25k with both cars I had 2 sets of discs and 2 sets pads on the front, rears no problem but afaik they all had the same problem
and yes I did use the power, but didn't like the fuel consumption lol
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Many drivers do not realise how hard they are driving, if they pulled up just after the last roundabout of say A43 Brackley by-pass section and touched the discs they would see what heat is being generated.
That is one of the arguments about using gears to slow a vehicle. That means dissipating kinetic energy, usually as heat, which often ends up in the discs and pads. By using the gears much of it ends up in compressing the contents of the cylinders instead.
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Good advice on the calipers, I had somewhat mistakenly assumed they had been changed. But yes, number 1 suspect here. Easy to check, just drive a few miles and very carefully check how hot they are, but the smell of burning pads will nearly always tell you first. They shouldnt be more than warm to hand hot, driven a few miles without much brake use, cool even. Dealers are notoriously reluctant to change calipers, as they'll cost a fortune on such a vehicle.
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Many drivers do not realise how hard they are driving, if they pulled up just after the last roundabout of say A43 Brackley by-pass section and touched the discs they would see what heat is being generated.
That is one of the arguments about using gears to slow a vehicle. That means dissipating kinetic energy, usually as heat, which often ends up in the discs and pads. By using the gears much of it ends up in compressing the contents of the cylinders instead.
I wonder if using the brakes to slow down is an issue in normal (non boy racer) driving? I suspect not.
Using the engine to help slow is normal practice when you are approaching a junction and take your foot off the accelerator. I don't think that is damaging, and can be part of gentle sympathetic driving.
However, when I learnt to drive, I would drop down a gear or two, forcing the engine to markedly slow the car, which is what I understand by engine braking, and surely this must put additional stresses on the gearbox and engine, which could shorten the life? The instructor never told me off, and only a few years later did I learn not to do that, and to use the brakes if I needed to shed speed more rapidly than just releasing the accelerator.
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These are my opinions only.
The vehicle is very new, and i suspect the driver has not allowed the brakes to bed in fully before subjecting them to hard treatment, until they are bedded in not all of the friction material area will be in uniform contact with the disc, this will create very hot spots where they are contacting, once warping of the disc has happened there is no fixing it other than refacing or replacing the disc, and if the same hard treatment before fully bedding happens again, the same results....100 miles of normal driving on normal roads should bed these new pads to the discs nicely.
It would be interesting to see the front wheels of this car after a typical week's driving, i suspect they will be caked in brake dust, i see this with my work vehicle where more brake dust on the front wheels can be created in my two days off than i can put on in 6 months, that is no exaggeration, it's confirmed by the reports the vehicle sends out, the vehicle itself also has friction material measuring on the dash menu.
Many drivers do not realise how hard they are driving, if they pulled up just after the last roundabout of say A43 Brackley by-pass section and touched the discs they would see what heat is being generated.
The recording equipment fitted to some especially higher range modern cars isn't exactly well publicised, many people appear to be content with total surveillance, so long as it's someone else unpopular being monitored and dealt with accordingly, makers are not going to be explaining all of this for obvious reasons, and it remains to be seen if the state forces makers(if they object at all?) to allow them access to this if they don't already have it with selective cases.
If i owned the car in question, first thing i would do is check for any brake binding, ie drive along a motorway or similar for a good distance without touching the brakes then stop at a convenient point without braking at all, it can be done easily with some forethought, then walk around the car feeling for any excess heat in the hubs/brakes...many vocational drivers practice this because such dragging will not be picked up at service times, it also helps diagnose early wheel bearing failure.
I would then drive the car more reasonably for at least 100 miles once fixed, and then if the problem persists, i would bin the undoubtedly hard OE pads and as an experiment stick a set of Brembos in the front and repeat the process and see what happens.
Cars do sometimes not have large enough brakes, not suggesting this is the case with this Audi and i doubt it has any relevance to this, Rover 827/Sterlings were a case in point, i bought an ex police driving school 827si many years ago, in the extensive police garage service history the car had received numerous sets of new front discs in its police time, probably every service so every few months, the car was an underrated flying machine of its time and warping of the front discs regularly continued during my ownership as well, a stop from 3 figure speeds would often mean a warped set of front discs as a result, the equivalent Honda had no such issues, though whether that was bigger brakes or a more gentle driving style due to the type of owner i don't know...i was younger and more shall we say enthusiastic in those days :-)
The OE brakes may well be Brembos anyway - the Porsche Cayenne/Audi Q7/Volkswagen Touareg SUV siblings all use them even in their lower-powered versions so no surprise if they're used on Audi S-models
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If i owned the car in question, first thing i would do is check for any brake binding, ie drive along a motorway or similar for a good distance without touching the brakes then stop at a convenient point without braking at all, it can be done easily with some forethought, then walk around the car feeling for any excess heat in the hubs/brakes...many vocational drivers practice this because such dragging will not be picked up at service times, it also helps diagnose early wheel bearing failure.
Check for binding using GB's method would be my first thought too.
Only ever had one warped disc, on the Xantia. Symptom was a shudder under braking (but not always present) shortly after new pads/discs were fitted. Dealer replaced without quibble. Could have been a failure on my part to wear them in but OTOH the Xantia's handbrake operates on the front discs so possible that created uneven cooling.
Dragging pads is something I've seen on several cars. Most distant in time was c1980 in my Mother's 1978 Renault 5. Most recent on current Berlingo about 6 weeks ago.
Ignoring the instances where the pads were smoking (both in BXs) then the 'catch' is often audible, particularly if it's at the front. Stops, or at least the tone alters, if you apply the brake.
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<< Only ever had one warped disc, on the Xantia. Symptom was a shudder under braking >>
One of our 205s developed braking pulsation at a fairly low mileage, about 10K IIRC. I had the discs skimmed, which cured it for a while, but the problem gradually returned, so I put it down to uneven metal in the discs.
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<< Only ever had one warped disc, on the Xantia. Symptom was a shudder under braking >>
One of our 205s developed braking pulsation at a fairly low mileage, about 10K IIRC. I had the discs skimmed, which cured it for a while, but the problem gradually returned, so I put it down to uneven metal in the discs.
I had this problem on a 309 (many similarities with 205s). Replaced front discs, but still had the problem.
Jacked up the rears, thought I had the reason, oval drums?
Skimmed the drums and refitted them, smooth rotation until I tightened the wheel nuts, when the 'oval drum' symptom returned.
I concluded that the alloy wheels were warped and bent the drums when fully torqued up.
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<< Skimmed the drums and refitted them, smooth rotation until I tightened the wheel nuts, when the 'oval drum' symptom returned. I concluded that the alloy wheels were warped and bent the drums when fully torqued up. >>
That's an interesting notion. It doesn't explain my difficulty, which only returned gradually. And my 205 was only a GR which had pleb steels ....
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It's always better to use the handbrake, if only to avoid dazzling the driver behind.
I agree. If intending to stop for more than a few seconds, I apply the handbrake. I think as we get older, the glare from brake lights becomes more irritating.
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I think as we get older, the glare from brake lights becomes more irritating.
Yes - but once the cataracts are replaced with artifical lenses, the vision goes back to normal.
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Reading all the comments it is likely the Audi has big drilled ventilated discs as standard to cope with its performance so AUDI's stance on the cars braking system does not make sense. Using the cars gearbox on modern cars hardly makes any difference to slowing the vehicle especially on modern autos and the modern train of thought is to use the brakes which is probably less strain on the transmission in any case
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It would be very interesting to check the disc run out with a dial gauge, confirm if they are really warping or if it's pad material transferring onto the disc by holding the brakes on hard after a harsh stop, so leaving high spots on the discs.
Either way, i'm not convinced the dealer would have mentioned the heat involved unless the car was genuinely grassing the driver up, that might have been a hint not to pursue things legally as they have digital evidence of exceptionally hard use, speeds, braking forces and gps pinpointing exactly where the incidences happened.
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Either way, i'm not convinced the dealer would have mentioned the heat involved unless the car was genuinely grassing the driver up, that might have been a hint not to pursue things legally as they have digital evidence of exceptionally hard use, speeds, braking forces and gps pinpointing exactly where the incidences happened.
Crikey! I hope my car is not spying on me, maybe the police should go straight to the dealerships instead of deploying traffic cops! Your honour, we plugged our laptop into the defendants car and found this!
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I had an '80s Ambassador that regularly warped its front discs. Replaced them a couple of times and flogged it with terrible brake judder.
I never got to the bottom of the problem, but it certainly wasn't over enthusiastic use of the 1.7L engine (worse I've eve had) and I never used to sit stationary with my foot on the brake.
The brake grab from the rear drums was another problem. No matter how much chamfer I filed on the leading edge of the rear shoes would cure it. Only happened for the first couple of applications, particularly in cold/damp weather.
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I think as we get older, the glare from brake lights becomes more irritating.
Yes - but once the cataracts are replaced with artifical lenses, the vision goes back to normal.
I have early stage cataracts, which are invisible except to the ophthalmologist, and typical for someone over 50. I suspect general aging of the eye (cornea, iris etc) is the main cause of glare for me, though the (very) early cataracts don’t help.
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"I have early stage cataracts, which are invisible except to the ophthalmologist, and typical for someone over 50. I suspect general aging of the eye (cornea, iris etc) is the main cause of glare for me, though the (very) early cataracts don’t help."
I'm in a similar position, but my incipient cataracts don't seem to affect my night vision and I don't suffer from glare. I suppose that cataracts, like many other conditions, don't behave in the same way for everyone.
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