Reading a nine year old copy of Autocar earlier this evening (in the bath!) and was intrigued by a comparison test between a standard Jaguar XK8 and a XKR SVO.
The road-tester kept mentioning how the standard car suffererd terribly from brake fade whereas the XKR with it's larger Brembo brakes did not.
Now although i've heard the term brake fade before i've never really understood what it means or it's implecations or indeed how to achieve it.
So in laymans terms could anyone in backroom explain this technical term and it's effects on ordinary motorists like me?
Have you had it?
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My basic understanding is this...brake fade = the braking capability/power is reduced during the period that the brakes are applied. Ie. they work very well when first braking but during the time you foot is on the pedal they start to lose their braking ability, requiring more effort to brake.
I hope that helps!
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When cold, brakes aren't particularly efficient. As they warm up they become more effective. BUT beyond a certain point, the hotter they get the worse they are at stopping you. That point marks the start of brake fade.
Years ago, in a Ford Cortina-Lotus Mk2, I had severe brake fade coming down Kirkstone Pass into Ambleside, behind a Morris 1000 - even in first I was struggling to avoid running into the back of it.
Modern materials and vehicle specifications make brake fade virtually unheard of, in road use.
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Modern materials and vehicle specifications make brake fade virtually unheard of, in road use.
unless you're driving quickly round Milton Keynes, 70mph limit dual carrigeways and roundabouts every half mile. Was the last time I suffered it, but unless you're stamping hard on the brakes regularly then you'll not see it unless you have very old brake fluid.
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I read often, only post occasionally
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When cold, brakes aren't particularly efficient. As they warm up they become more effective. >> Modern materials and vehicle specifications make brake fade virtually unheard of, in road use.
Hmm that's interesting so i suppose my car is simular to an F1 car in that respect. What about warming up brakes a la F1 before use on a road car or is that a silly suggestion. So if they achieved this in a 9yo Jaguar the brakes must be pretty poor on this car.
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A magazine road-testing a car is hardly "normal" road use! Initiating brake fade, what ever it takes, is one of their "standard" tests. All cars will fade at some point, in these conditions, that doesn't make a standard XK8 bad!
What make of car is best avoided around Milton Keynes?
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A magazine road-testing a car is hardly "normal" road use!
well yes your're correct, i accept that, but why do they feel the need to mention it.. (several times?) if the test is irrelevant?
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I have never felt in in a car, but have had a couple of interesting moments in fully laden artics where the brakes have become a bit soft at the end of a long down hill stretch, not in any recent makes though, this is going back about 8 years, so either I now use the brakes less or the manufacturers have improved them!
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its caused by severe overheating of discs and pads,the pads on contact with disc cause friction(this creates heat)to overcome this problem on discs holes are drilled-to help dissipate heat using the airflow/other materials are used in discs to help clear away heat or dissipate,Pads can also be made up of various materials to do same job ie clear the heat from pads as fast as possible..so the cooler the disc/pad stays better your braking
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Steve
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I've boiled the fluid on a 2CV-drum brake of course,gets hot round the back of the engine.
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As far as I can see no one has mentioned drum brakes. They are more prone to fade than discs because the expansion of the drum as its temperature increases takes the drum further away from the shoes, requiring a 'longer pedal' which in extreme cases reaches the floor. The arrival of front, and now almost universal four-wheel, disc brakes has virtually eliminated fade from ordinary motoring. Corroded, wet or dirty discs, pads worn down to the metal, seizing pistons etc are likely causes of fade with discs. When Jaguar pioneered them at Le Mans in the C-type, the glow of the discs in the night at the end of the Mulsanne straight went down in history. But they didn't complain about fade. Same with F1 cars which often make their carbon discs red hot.
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We need to distinguish between brake fade (which is where the pedal feels the same but the brakes don't slow the car as much as when the pads/shoes are cool) and boiling the brake fluid (which gives you a soft pedal, often all the way down to the floor).
To put it another way, brake fade is when there is a strong smell of brake linings when you get out of the car after the crash, and boiling brake fluid will mysteriously put itself right as the system cools. Neither event is to be recommended as a leisure pursuit.
I did get brake fade in a Mk 1 Cavalier estate trying to keep up with an expertly driven Citroen CX coming from Cookridge to Otley down Otley Old Road many moons ago.
Hawkeye
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Stranger in a strange land
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I think it is fair to say that there aren't many 'decent' modern cars when driven reasonably on the road, that will ver suffer from brake-fade. About the only way you will usually see this phenomenon is to brake from say 90 mph as hard as you can on a deserted stretch of motorway. If you see brake fade at any other time on the road, you are either driving in a bonkers way, or towing too heavy a load on an unbraked trailer.
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or cleaning the discs up after car been stood a while.
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I used to get horrendous brake fade on my Ford Ka. Hills such as Gore Hill in Amersham, used to be a good test of engine braking and slowing down nicely from the top of the hill (even with tail gaters trying to drive over me).
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Probably why they have ventilated discs as standard now.
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Never suffered from it in the car but had it on the mountain bike on some steep descents where I've been leaning on the brakes the whole way.
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"...but had it on the mountain bike on some steep descents where I've been leaning on the brakes the whole way."
That seems to sum it up. In a car : use your gears and don't bother about the guy behind who wants you to go faster.
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I had it a while ago in my car. Pretty scary really - especially the harsh realisation when you press the pedal more and more and nothing much happens!
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Change the brake fluid Adam.
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Why? It must have been 4 months ago now. Does something bad happen to it when it happens?
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Does something bad happen to it when it happens? How vague.
Does something bad happen to the brake fluid when brake fade occurs?
There - that's better.
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Could have boiled it....bad. When did you last change it ?
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Much as I'm going to sound cavalier when it comes to car maintenance, my Dad's mate sorts it all out come service time. If it got changed during the service, then August - if not, I have no idea. I can find out though.
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Much as I'm going to sound cavalier when it comes to car maintenance, my Dad's mate sorts it all out come service time. If it got changed during the service, then August - if not, I have no idea. I can find out though.
You'd know if you'd boiled the brake fluid - it's terrifying when the pedal goes to the floor and there's no perceptible retardation. Unless the fluid is very degraded you'd have to try really really hard to achieve this other than when descending an alpine pass.
Brake fade has nothing to do with the fluid, just very hot brakes not working as well as they should. They will normally recover when they cool down.
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Yeah the brakes have been fine ever since and stop the car perfectly.
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When a penniless student I drove an immaculate Rover 16 made in 1946. 2 litre engine large drum brakes all round and front opening front and rear doors.
Brake fade down steep hills was a constant issue. Worst was the Cockbridge to Tomintoul road with lots of very steep hills. All 4 drums would become hotter, the smell of burning brake linings (well asbestos so just very hot) and external drum paint burning became intolerable so I had to slow down and stop and wait for the drums to cool down and brake pedal travel to return to normal. (the car weighed 1.5 tonnes iirc and it had rod operated brakes with beam axles - very efficient when cold.)
Normal braking on 17inch tyres (5.50x17 iirc) was quite good but grip of course was low and accleration was I believe timed by Autocar at 0-60mph in 21 seconds so it was hardly a speedster!
A lovely car in British racing Green but the steering was Very heavy when parking and with a front beam axle and elliptic springs, axle tramp over cobbles or some potholes was a terrifying and ever present threat..
Oh the joys of motoring! NOT.
Nostalgia for the past is just that. Cars were heavy to drive, unreliable and required servicing every 1,000 miles. I don't regret any of the passing of having to decarbnise it/replace brurned out valves, reline the brake shoes (yes: reline them with new linings riveting the new ones on), changing contact brekares, etc. At least it had force fed chassis lubrication which saved frequent greasing - when it worked!
And modern cars do not have brake fade (had it on a front disk braked Rover 75 on the same road...)
madf
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Axle tramp?
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Uncontrolled oscillation of a beam axle. This can be sufficiently violent to lift a wheel completely off the ground.
On a driven axle, this can be a self excited vibration, taking energy from the drive torque.
On a front axle, the extra degree of freedom offered by the kingpin allows tramp to become more complex, generally called shimmy. The gyroscopic behaviour of the rotating wheel couples moments in the camber direction with steer axis moments which are felt as vibrations at the steering wheel.
Better axle location can reduce the efficacy off the self excitation mechanism, albeit at the cost of extra transmitted noise and vibration to the car body. Improved damping also helps, by removing the vibrational energy, and converting it to heat in the damper.
Number_Cruncher
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There can be many reasons for a reduction in actual or percieved braking efficiency however "fade" refers to the effect caused by the surface of the pad melting and therefore reducing the amount of friction between the pad and disc. My Dolomite Sprint used to suffer from this, the brakes were just not up to the job, revised pads (can't remember the spec) helped though required more of a heave on the pedal when cold.
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