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Old 10th January 2010, 05:36   #46
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Default ABS - a detailed write-up.

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Originally Posted by EssYouWe View Post
PS: The mechanical ABS thingy was neat!
For Those who are interested -
Here is a detailed write-up about ABS from Anti-lock Braking Systems


ABS

Introduction
ABS stands for “anti-lock braking system,” or “advanced braking system,” depending on whom you ask. It does, pretty much, what it says in the title, but as we shall see, there are several different types of ABS that have been, and currently are, available in the market. ABS was originally used in aerospace applications - specifically, to reduce wear and tear on aircraft tyres after landing, caused by flat spots. Now if you consider the replacement cost of a single Boeing 747 tyre, then consider how many tyres they have...
ABS is usually bundled together with EBD, Electronic Brakeforce Distribution.
What Does It Do?

If the ABS light is illuminated whilst driving along, it has developed a problem.


In simple terms, ABS is designed to help the driver maintain control during an emergency-braking manoeuvre. It does this by either preventing the wheels from locking, or if they do lock, by releasing and then reapplying the brakes once more. This is because when a tyre is locked, it provides very little directional stability. On other words, you cannot steer with a locked front wheel, and a rear wheel will tend to go wherever inertia sends it.
In effect, it is a mechanical way of cadence braking (except it may be either controlled by a mechanical or electronic system). There are two advantages of using ABS over non-ABS brakes for the typical driver. One is that the ABS system is able to “pump” the brakes on and off much quicker than the driver’s leg, and the other is that it requires no skill or experience - the car does all of that for you.
When you do an emergency stop in a car, it is important to dump the clutch as soon as you hit the brakes, rather than delaying it (as you were probably taught in a non-ABS car that you took your driving test in). If you keep the clutch in, the ABS system has to cope with both the forward momentum of the car and the engine at the same time.
ABS Helps You Stop?
In simplistic terms the braking effort on the wheel when ABS is working varies from a locked wheel (or a nearly locked wheel) to no brakes being applied at all. Even if the system goes from one extreme to the other many times a second, the average braking effort will be less than “full on.” Therefore, do not assume that ABS always shortens stopping distances.
To go into slightly more technical detail, the maximum possible braking effort is achieved just as the wheel decelerates rapidly compared to the road speed, called the retardation point. In other words, a very slight skid. Most ABS systems detect that a wheel is locking by detecting this rapid wheel deceleration (which is in no way similar to a wheel under ordinary braking and so relatively easy to detect). The system then releases the brake for that wheel.
ABS systems optimised for racing track performance are designed to release the brake just enough to start the wheel accelerating once more before reapplying the brake. They are able to keep the wheel at the retardation point and so may maximise braking efficiency. The compromise with this form of ABS is that the driver has almost no more steering control compared to a locked wheel – these ABS systems are designed to stop the car in as short a possible distance and so are of less use for the road.
Thus, conventional ABS systems as fitted to road going cars do not stop the car any shorter than non-ABS brakes. A skilled driver will be able to pull up the non-ABS car in a shorter distance compared to the driver using ABS. However, there is almost no skill involved when performing an emergency stop using ABS. Any driver is able to stop as quickly as possible whilst keeping the car pointing in their intended direction.
It is possible to fool the ABS system if you are reckless enough, but you do have to be doing something rather foolish and I’m certainly not going to tell you how to do it here. J
Mechanical and Electronic Systems
As you would expect, mechanical ABS use a “nuts and bolts” method of detecting when the wheel has slowed down too much, and electronic systems use clever little gizmos. Mechanical systems are less sophisticated, and usually do not work at very slow speeds - one example is the mark three Fiesta, which only works above 20 mph. They also tend to require more space inside the car, which is a consideration for all cars, but more so the smaller ones. Finally, mechanical systems do not tend to work on all four wheels. There may be a split front / rear system or both individual front wheels have their own sensor and both rear wheels use the same one.
On the plus size, mechanical systems tend to be more robust, and for high speed applications where space is not so pressing (such as the aforementioned Jumbo Jet), they are useful.
Electronic systems do not require so much space and are much more sophisticated - they can work at much lower speeds. Kermy’s handbook reports that his ABS works at all speeds above 4 mph but it works right down to just before you stop. All current production cars sold in the UK have an electronic system.
ABS Kicks Back!
Different cars do different things when the ABS kicks in, but in most cases, the brake pedal kicks back. If you have never experienced this, it is quite an unusual experience - and some drivers are reputed to ease off the pedal at this. With ABS in an emergency situation, this is precisely the wrong thing do to (and one of the reasons why many manufacturers use Emergency Brake Assist). In some cars, the system makes a racket, which can also be off-putting. The Ka’s ABS sounds a bit like the brakes are grinding against gravel!
Over-Enthusiastic ABS?

I hammered those brakes - note how the nose is rather low!


Some people have complained that the ABS in their car seems a bit too keen to kick in. These individuals are often used to a car without ABS and are assuming that there is more grip available from the tyres than they have. In most front wheel drive cars it is very difficult to detect a rear wheel starting to lock up until it turns into a proper skid, whereas the ABS spots this.
It is not beyond the realms of possibility that ABS manufacturers deliberately set up their ABS to be a little bit more enthusiastic than is strictly necessary, however, if we ignore this at present the ABS is a warning that conditions under the wheels are not as rosy as they may appear. Whilst some modern car designs do appear to paint a vivid picture of what the road is like, in reality, they isolate the driver from the road condition (ask any racing driver!).
We may not feel the skid itself, just feel the ABS kicking in – and that’s probably a good thing.
ABS and Winter Conditions
Some cars had an ABS override switch, several Audi models for example, whereby the driver could manually turn the system off.
Why would you want to do this? There are two reasons - one being that an experienced driver might want to eke out a bit more braking performance at a track day (see below), and the other being that you were driving on a snow covered road (or indeed, on gravel driveways). This is because snow building up in front of a locked wheel improves braking performance. Of course, with ABS, this does not happen since the wheel is not locked for long enough! For some (foolish) drivers, the perceived dismal braking performance of ABS equipped cars can come as a big surprise in snowy conditions!
This picture right illustrates what the Ka’s ABS does (not just in winter, but it’s easier to see on snow). When the wheel locks, the system releases the brake – each wheel is braked independently. The darker patches show when the wheel locked. Note that the Ka “wiggled” during braking – but it kept pointing in the right direction.
You’ll all see some Dervy Footprints, but you can’t see where Dervy fell over – the flash didn’t quite reach that far!
To watch Kermit’s ABS in action on snow, go here.
ABS and Track Day Use
Many people consider ABS to be a handicap on a track day or for competition use because it makes the braking inefficient (in other words, you take longer to slow down). For almost cars, this is quite accurate – the ABS system is optimised to retain car control over ultimate braking power and this is certainly true over all Fords I’ve driven including the Ka.
An anti-lock system can be designed with competition use in mind – that is, for maximising braking effort. Systems designed for road-going cars are compromised in this respect.
The Ka’s ABS System – Under Pressure
For the purposes of writing this article, and for testing how resistant the Ka’s brakes are to fade, I took Kermit down a steep section of road. Visualise a twisty two mile section of road. Now imagine it has an average gradient of 25% and your objective is to go down this as quickly, and as safely, as possible. That means keeping your speed down so that you can stop in the distance that you can see . . . and to make some of the tighter corners, of course!
This road passes from the top of Sutton Bank, near Thirsk in Yorkshire, down past the White Horse (a good photo opportunity as illustrated), and is composed of short straits with tight hairpins at either end, running through a beautiful forest. It’s lovely scenery, but you have to be careful of the wild life, which has a habit of jumping in front of traffic (and I don’t just been bunny rabbits, either).
Hacking down this hill, braking heavily on the approach to each corner, the Ka’s ABS wasn’t doing anything – apart from the approach to the tightest corner, which happens to be after the longest strait. We approach at 60 in third. There is a large bump on the approach to this corner and I’m anticipating the ABS to kick in once we’re the far side of it. We reach it under hard braking, the nose low, and as we go over, the ABS does its thing. It’s stopped pulsing as we reach the corner, snatch second and around we go.
Kermit’s ABS on Standard Suspension

Kermit’s ABS is a four channel electronic system. I don’t make a habit of using it, actually before we had the Ford Racing Suspension fitted I can count on one hand the number of occasions when I triggered it (away from me deliberately triggering it on snow or ice).
With the standard suspension set up the Ka’s nose drops quite a bit under firm braking. Drive over a rough road surface, a grill or a white line and if any wheel is going to trigger the ABS under firm braking it will probably be at the rear. As the driver, one would very rarely feel this happen but you’d hear the clicking noise as the ABS cycles the brakes.
There is an exception to every rule. When we first put the XR2i wheels on the kid they were wearing Wynstar tyres. As I have alluded to elsewhere in this website, in wet weather his behaviour was a little untoward. Under just moderate braking the ABS would kick in on any wheel as it lost grip. This was one of the main reasons why I decided to get rid of the Wynstars and replace with Falken ZE502s!
Kermit’s ABS on Ford Racing Suspension

By the time we put the Ford Racing Suspension on Kermit, we also had the [strut brace fitted and the XR2i wheels were wearing Falken tyres. With these modifications and under ideal conditions, the lad’s ability to handle acceleration (as in changes in velocity, so acceleration, braking and cornering) were very much improved. I was able to brake harder and longer without triggering the ABS and when it did kick in, it would either be the front or the rear wheel that needed the assistance rather than almost always the rear wheel. Using the Ford Racing suspension has effectively balanced out the braking effort with the ability for that corner to decelerate the Ka.

Last edited by Samurai : 10th January 2010 at 11:37. Reason: font tags removed
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Old 10th January 2010, 10:17   #47
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Oops.. dont copy and paste from a website directly! Paste it in Notepad, and then over here. Its going to be one tough job for the moderators to clear the font/ colour html codes from your post!
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Old 25th March 2010, 10:35   #48
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Originally Posted by SamtheLeo View Post
I own a Grande Punto & most of the time only when you are travelling at very very low speeds & tend to brake hard then you hear a "drrtttt" sound & thats all. No squealing, neither judder. All goes with out any issues.
I tried that in few puntos and seems like its a usual thing with Punto
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Old 13th December 2013, 20:11   #49
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Sorry for reviving an old thread.

I own a 2009 Punto. The problem I'm facing usually happens at very low speeds and when the brake pedal is slightly pressed. There is a KRR-KRRR crunching kind of sound and I can sense some movement in the brake pedal too (slight upward push). I can feel the brakes engage-disengage-engage rapidly (car slows down, sort of jerks and moves comparatively a little bit faster, again slows down).
A quick read through this thread suggests it's ABS at work, but, in my case, this is happening on very light braking (almost a slight tap on the brakes and only at very low speeds).
Ps- I've had the pads replaced, but still the problem persists.
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Old 14th December 2013, 23:11   #50
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Originally Posted by schakravarthy View Post
Sorry for reviving an old thread.

I own a 2009 Punto. The problem I'm facing usually happens at very low speeds and when the brake pedal is slightly pressed. There is a KRR-KRRR crunching kind of sound and I can sense some movement in the brake pedal too (slight upward push). I can feel the brakes engage-disengage-engage rapidly (car slows down, sort of jerks and moves comparatively a little bit faster, again slows down).
A quick read through this thread suggests it's ABS at work, but, in my case, this is happening on very light braking (almost a slight tap on the brakes and only at very low speeds).
Ps- I've had the pads replaced, but still the problem persists.
Are the pads set in correctly with the necessary clearances? As the grinding sound is heard on light press of the pedal just check the clearance and get the brake fluid bleeding done once (if not done)

I feel the pads are rubbing against something so that sound.

Anurag.
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Old 14th December 2013, 23:16   #51
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Originally Posted by a4anurag View Post

Are the pads set in correctly with the necessary clearances? As the grinding sound is heard on light press of the pedal just check the clearance and get the brake fluid bleeding done once (if not done)

I feel the pads are rubbing against something so that sound.

Anurag.
The issue was present even before the pads were changed, so I feel clearance might not be the issue here. Just to be sure, I'll check again and revert. Thank you.
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Old 14th December 2013, 23:52   #52
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Originally Posted by schakravarthy View Post

The issue was present even before the pads were changed, so I feel clearance might not be the issue here. Just to be sure, I'll check again and revert. Thank you.
Check for the proper working of the pistons.

Anurag
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Old 14th December 2013, 23:59   #53
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Originally Posted by a4anurag View Post

Check for the proper working of the pistons.

Anurag
So you don't feel something might be wrong with the ABS sensors? After all, all the symptoms resemble that of ABS action, expect the all important hard braking!
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Old 15th December 2013, 07:43   #54
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Originally Posted by schakravarthy View Post

So you don't feel something might be wrong with the ABS sensors? After all, all the symptoms resemble that of ABS action, expect the all important hard braking!
Why directly jump into the ABS Module and its function. Let's check the basic stuff and if still no use then the ABS needs an eye.

Anurag.
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Old 15th December 2013, 09:51   #55
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Default Re: Strange ABS behaviour in Fiat Punto

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Originally Posted by schakravarthy View Post
Sorry for reviving an old thread.

I own a 2009 Punto. The problem I'm facing usually happens at very low speeds and when the brake pedal is slightly pressed. There is a KRR-KRRR crunching kind of sound and I can sense some movement in the brake pedal too (slight upward push). I can feel the brakes engage-disengage-engage rapidly (car slows down, sort of jerks and moves comparatively a little bit faster, again slows down).
A quick read through this thread suggests it's ABS at work, but, in my case, this is happening on very light braking (almost a slight tap on the brakes and only at very low speeds).
Ps- I've had the pads replaced, but still the problem persists.
ABS kicking in early happens when the tyres are towards the end of their life causing them to lose traction easily making the ABS kick in early. You could also check your suspension systems too as weak suspensions also lead to loss in traction making the ABS kick in early too. I do not think there would be a problem with your ABS.
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Old 15th December 2013, 11:16   #56
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Originally Posted by VeyronSuperSprt View Post

ABS kicking in early happens when the tyres are towards the end of their life causing them to lose traction easily making the ABS kick in early. You could also check your suspension systems too as weak suspensions also lead to loss in traction making the ABS kick in early too. I do not think there would be a problem with your ABS.
The tyres have around 5k-7k kms left in them. Could you please elaborate on the suspension part? The issue I'm facing happens at near crawling speeds, say around 10kmph or less. Will a weak suspension cause erratic ABS behaviour at those speeds?
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Old 15th December 2013, 12:00   #57
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The tyres have around 5k-7k kms left in them. Could you please elaborate on the suspension part? The issue I'm facing happens at near crawling speeds, say around 10kmph or less. Will a weak suspension cause erratic ABS behaviour at those speeds?
If the tyres have only around 5k left in them, then they are most likely to be the cause although kicking in at 10kmph is very early unless you applied the brakes in a sandy/muddy/gravelly area. It is possible that the tyres have been damaged/ have cracks which further reduce traction. It would be good to first change your set of Tyres, there would be a difference. You must also be experiencing a bit of instability at speeds. From what you have written, it would not be the suspension.
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Old 15th December 2013, 12:16   #58
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Originally Posted by VeyronSuperSprt View Post

If the tyres have only around 5k left in them, then they are most likely to be the cause although kicking in at 10kmph is very early unless you applied the brakes in a sandy/muddy/gravelly area. It is possible that the tyres have been damaged/ have cracks which further reduce traction. It would be good to first change your set of Tyres, there would be a difference. You must also be experiencing a bit of instability at speeds. From what you have written, it would not be the suspension.
I was told that one of my alloy wheels has a slight bend. I face steering vibrations at exactly 80kmph-90kmph. Could that be related?
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Old 15th December 2013, 13:54   #59
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Originally Posted by VeyronSuperSprt View Post

If the tyres have only around 5k left in them, then they are most likely to be the cause although kicking in at 10kmph is very early unless you applied the brakes in a sandy/muddy/gravelly area. It is possible that the tyres have been damaged/ have cracks which further reduce traction. It would be good to first change your set of Tyres, there would be a difference. You must also be experiencing a bit of instability at speeds. From what you have written, it would not be the suspension.
I am not able to understand the thread avaliable to the ABS link! Please elaborate if you don't mind. You mean due to low traction the ABS is kicking in?

AFAIK generally the ABS kicks in at high speed rather than 10 kmph!

Anurag
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Old 15th December 2013, 14:32   #60
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I was told that one of my alloy wheels has a slight bend. I face steering vibrations at exactly 80kmph-90kmph. Could that be related?
First check your tyres for damages as it would be possible if your alloys are bent, then the tyres would have even more damage. This would lead to loss of traction.

Quote:
Originally Posted by a4anurag View Post
I am not able to understand the thread avaliable to the ABS link! Please elaborate if you don't mind. You mean due to low traction the ABS is kicking in?

AFAIK generally the ABS kicks in at high speed rather than 10 kmph!

Anurag
ABS kicks in only when there is loss of traction and is not connected to speed except to the extent that it is usually at high speeds that traction is lost. Loss of traction can happen at any speed - even at 10kmph at very slippery surfaces resulting in the ABS kicking in.
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