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Old 27th September 2009, 00:47   #16
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It should pulsate. But the tyres can squeal a bit. Remember that ABS keeps your wheels at the threshold of braking. Some particularly noisy tyres can squeal even when they are about to lock up.

The ABS light illuminating when ABS is at work is not guaranteed across all cars. Some have it, just like how traction and stability control lights work. But most have it illuminate only when there is a fault.
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Old 27th September 2009, 00:58   #17
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Quote:
Originally Posted by McLaren Rulez View Post
AFAIK, the light should be on if ABS is working at that moment.
Does that happen for any car? AFAIK, in present day cars ABS light comes on only when a fault is detected with the ABS system or sensors and its doesnt happen with either Linea or Punto, light comes on only when ABS system is at fault.
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Originally Posted by sukrit7 View Post
@Mclaren- well that certainly doesn't happen?
hmm, linea and punto owners, please clarify?
Sukrit, one suggestion for you.
Just find an empty stretch of road which you know (preferably you know if any speed breaker or pothole isnt there), just take your Punto to 90-100, reconfirm that noone is behind you and then just stomp your foot on the brakes, keep the pedal pressed hard and twitch your steering a little bit to left or right, if car moves even 2 inches in response to your steering input then ABS is fine and theres no need to visit TASS.

Last edited by coolboy007 : 27th September 2009 at 01:00.
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Old 27th September 2009, 01:41   #18
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Quote:
Originally Posted by sukrit7 View Post
I own an emotion pack multijet punto, about 4500km and 2 months old. This is my first abs equipped vehicle and hence the question. From whatever I know of abs it prevents the car from going into a skid, the wheels are not supposed to lock up so that you can turn while braking easily.

In the ford fusion I drove daybefore the brake pedal pounded against my foot on hard braking as it supposed to happen in abs vehicles, am I right ?
In my punto this never happens, and under hard breaking the car remains composed and straight but the tyres do squel, and sometimes quite loudly; as I said before the brake pedal never vibrates against my foot as I believe is supposed to happen.
Please provide your inputs.
Take it onto a gravel road, and slam the brakes while making sure it is safe to do so. That way you will get used to what the ABS will do, and it will not come as a surprise in an emergency braking situation. The tyres does squeal occassionally in ABS cars too, from my observation. Nothing to get alarmed about. Different vehicles have different ABS calibration, and pulsation is different as well.
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Old 27th September 2009, 17:58   #19
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Dash light for ABS should come on *only* to show a fault, not otherwise - that is the convention.

With ABS, the pedal *has to shudder* - no way that can be avoided. This is because brake pedal acts direct on the hydraulic system. (This is the only system in the car that probably will never be controlled 'by wire' - massive human liability prevents manufacturers from switching to total electronic). With the hydraulically amplified force acting on the brake actuator when you brake, the ABS system bleeds the brake line near the brake actuator for a short duration repeatedly, so that the effective pressure at the actuator reduces for a short while and the brake drum/disc is not grabbed by the brake lining. This reduction and the subsequent pressure build-up (instantaneous) gets fed back to the brake pedal and your foot (which is pressing the pedal).

The action is on ALL 4 wheels (as well as trailer brakes, if a trailer with ABS is hitched). Actually, *whichever* wheel is locking up will have it's ABS valve pulsed, which means ALL if all wheels are locking up. The ABS acts on wheel lockup independent of vehicle speed.

In this process, tyres *can* squeal, but only if the tyre compound is relatively hard. Even is that case the 'squeal' will be a lower frequency and softer than a 'squeal' without ABS.

Service center would have a portable diagnostic equipment which can be plugged into the ECU (usually in the dash somewhere). This tool is able to show if the ABS valves are acting when braking, as well as exercise the valves at stand-still (one can hear the valve click if you listen closely near the wheel). Wheel speed sensor (mounted at the wheel) failure will switch on the 'ABS system failure' light on the dash.

Last edited by DerAlte : 27th September 2009 at 18:00.
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Old 28th September 2009, 15:32   #20
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Quote:
Originally Posted by DerAlte View Post
Dash light for ABS should come on *only* to show a fault, not otherwise - that is the convention.

With ABS, the pedal *has to shudder* - no way that can be avoided. This is because brake pedal acts direct on the hydraulic system.
Yes it shudders. But some cars able to keep it under acceptable limits or let's say gentle, while it feels like a mad puppy under your foot under some. And yes, I like to test ABS in all the cars that I drive.
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Old 28th September 2009, 16:01   #21
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Quote:
Originally Posted by ImmortalZ View Post
It should pulsate. But the tyres can squeal a bit. Remember that ABS keeps your wheels at the threshold of braking. Some particularly noisy tyres can squeal even when they are about to lock up.

The ABS light illuminating when ABS is at work is not guaranteed across all cars. Some have it, just like how traction and stability control lights work. But most have it illuminate only when there is a fault.
Ditto... I drove the Fiesta ABS and the tyres did squeal but never locked up.
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Old 28th September 2009, 16:44   #22
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@sukrit7- Just checking, did you change/ upsize your tires or rims?
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Old 28th September 2009, 17:09   #23
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Okay, looks like I was wrong about the light being on whenever it worked. Anyway, doesn't tyre squeal mean that the wheel has locked up? Why else would it squeal?
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Old 28th September 2009, 18:11   #24
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No, tyre squeal does not mean that it has locked up. It just means that the tyre has reached the break even point. It is after this that the tyres lock up, but in this case, the ABS works and prevents the screech after the squeal.

It is just a case of the brand/quality of tyres here. Maybe Sukrit is running the pressure too high?
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Old 28th September 2009, 18:24   #25
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Here's a picture for you guys to analyze.
There are two pairs of tyre skidmarks. The one on the left is from a vehicle WITH ABS and the one on the right is from a vehicle WITHOUT abs.
Attached Thumbnails
Strange ABS behaviour in Fiat Punto-27588252_059f64750d_o.jpg  

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Old 28th September 2009, 18:31   #26
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The squeal / screech (both are the same sound, right?) is the audible indication of the tyre rubber losing grip on dry tarmac. It won't squeal on sand and wet surface - sand grains roll, liquids lubricate the rubber/tarmac boundary. The sound is the result of hundreds of points of tyre rubber getting snagged on the sharp points of the tarmac and releasing - imagine hundreds of rubber bands snapping. Add the tiny amount of gas / smoke produced by the heat of friction on rubber, and it is a crazy scene there.

This can happen without the tyres locking up, like too much torque on the wheel or too much sideways force while cornering. Wheels locking up is the same situation - car's momentum overcoming tyre adhesion.

Last edited by DerAlte : 28th September 2009 at 18:34.
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Old 29th September 2009, 02:14   #27
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DerAlte is right - the squealing is not the wheels locking up, but more of it being at the 'threshold'.

I had to slam the brakes in Dad's Linea a few days earlier and noticed the tyres squealing as well. Thought the ABS wasn't working and was getting ready to drive the car through the showroom . Coincidentally your thread popped up as well.

Went out for a spin just now to test it out a couple of times, and while the tyres do squeal, they are in short *bursts* indicating they are being kept at the threshold. I just noticed nitrous' pic and the skid-marks seem to show that same pattern. However, the brake pedal wasn't bouncing madly.. instead there was a faint juddering but a very audible thud-thud sound from the wheels. The ABS light does not come on. So if you need reassurance that your ABS is working - the loud thud-thud from the wheels would be it.
For reference, I tried this out on Michelin Primacy LC tyres at speeds of about 60~80 kmph.

Last edited by Crazy_Eddy : 29th September 2009 at 02:18.
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Old 29th September 2009, 10:07   #28
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LOL The brake pedal doesn't ever 'bounce madly', it is more like the sensation from an electric massager.

The 'thud-thud' is a worrying sound, though - it means that interval between ABS releasing the brake and grabbing it is a bit too long. As long as the vehicle did not deviate from a straight line while braking, even that is fine. Different makes of ABS handle this duty factor differently. Which make is Linea ABS - Magneti Marelli or Bosch?
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Old 29th September 2009, 22:33   #29
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^ I'll admit this is the first time I'm experiencing ABS, so no point of reference there... I just got the impression the pedal usually shudders violently from the descriptions here

The thud-thud was the closest I could think of for the sound, but the interval wasn't that far apart, say about ~5 times a second?

No clue who makes the ABS on the Linea. How do I check?
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Old 30th September 2009, 00:57   #30
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AFAIK, the ABS system on Linea is from Bosch.
When the service personnel had connected Tech2 scanner to my cars ECU to match correct keycode card (had been mixed with other Linea cards), there so many parts were from BOSCH. I think i read something as Bosch ABS there.
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