Please solve Citroen Xantia ASB brake debate

frenchcarnut · Post by **frenchcarnut** » 25 Jul 2007, 15:09

Hi there, nice forum.

Had this argument over whether or not you could feel and hear the ABS braking system when applied.

I said you could feel the pulse and some pedal drop - even hear grinding. Opponent totally denied this saying that the pulse was so fast, one couldn't feel it or know when ABS was acting.

Am I going mad? And were the ABS symptoms I felt and heard just a figment of my imagination?

Now owner of C5 Auto Diesel VTR - nice car

Post by **CitroJim** » 25 Jul 2007, 15:25

Hi and welcome to the forum!

On a conventional car with conventional ABS I believe you will feel the ABS working with a pulsing pedal.

On a Hydraulic Citroen though, a full hydraulic one but not your C5 which is, as I understand, pretty conventional in its braking, you won't feel it anywhere so much, just the effects of ABS bringing you very quickly to a controlled halt.

I have invoked the ABS a few times on both my Xantias, both on-purpose to test and during emergencies. All that happened was a controlled stop.
On my TD Xantia the ABS was non-operational when I first had the vehicle due to a duff sensor. After replacement of the sensor the difference was quite amazing. An emergency stop changed from being a full 4-wheel skid to a ful stop with no drama whatsoever whith no change of feeling in the pedal.

Post by **RichardW** » 25 Jul 2007, 15:49

I can definitely feel and hear the ABS if it kicks in on my Xantia. Mind you, that's only twice in anger in 60k miles

I always test the surface on frosty mornings though, and get the ABS to kick in - gives some reassurance that it's working, rather than just the idiot light

frenchcarnut · Post by **frenchcarnut** » 25 Jul 2007, 15:50

citrojim wrote:Hi and welcome to the forum!

On a conventional car with conventional ABS I believe you will feel the ABS working with a pulsing pedal.

On a Hydraulic Citroen though, a full hydraulic one but not your C5 which is, as I understand, pretty conventional in its braking, you won't feel it anywhere so much, just the effects of ABS bringing you very quickly to a controlled halt.

I have invoked the ABS a few times on both my Xantias, both on-purpose to test and during emergencies. All that happened was a controlled stop.
On my TD Xantia the ABS was non-operational when I first had the vehicle due to a duff sensor. After replacement of the sensor the difference was quite amazing. An emergency stop changed from being a full 4-wheel skid to a ful stop with no drama whatsoever whith no change of feeling in the pedal.

I used to feel mine all the time when it was working. It was like a nibble on the pedal. Anyway, the debate surrounded ABS in general, so I think I was fairly accurate.

frenchcarnut · Post by **frenchcarnut** » 25 Jul 2007, 15:57

RichardW wrote:I always test the surface on frosty mornings though, and get the ABS to kick in

That's what I used to do with mine - especially since I had a couple of failed sensors over the 7 years I had it.

No doubt into the second year of my C5 I will doing the same

jeremy · Post by **jeremy** » 25 Jul 2007, 15:57

I've got it on my BX but I've only had it come on at slow speeds - when to be honest I wish it hadn't been there - like the time I nearly got a neighbour's cat as by the time the thing made its third pulse the car would have stopped with the wheels locked. I had a similar experience when someone opened a car door immediately in front of me in a narrow road with cars parked both sides. - How to make a crisis out of a drama.

In fact I drove the car for 6 months before I got it working - and I must say that to be honest out of all the cars I've had it needed it least.

My view of it is that at all costs I must drive carefully enough to prevent it working as although the car will not slew if it does cut in, its almost certain to increase my stopping distance.

We don't get much snow in Sunny Southampton but when we did get a little I tried it out just to see what happened - and again the thing seemed less likely to stop with it working that without. Certainly not a case of slamming on the brakes and coming to a smooth and rapid stop.

I think I get a certain amount of feedback through the pedal which is to be expected as the doseur displaces pressurised fluid as it operates - and so if the pressure of the fluid displaced varies - the pressure exerted on the valve - and eventually the pedal will vary as well.

frenchcarnut · Post by **frenchcarnut** » 25 Jul 2007, 16:00

jeremy wrote:I think I get a certain amount of feedback through the pedal which is to be expected as the doseur displaces pressurised fluid as it operates - and so if the pressure of the fluid displaced varies - the pressure exerted on the valve - and eventually the pedal will vary as well.

Well that sounds like a fairly credible theory whilst the rate of pressure change due to fluid displacement would be different to action of the valve itself given physical constraints.

I've also read an academic abstract alluding to the issue of noise being down to action matching resonant frequencies within the structure of the car when the ABS kicks in.

jeremy · Post by **jeremy** » 25 Jul 2007, 16:08

That probably accounts for the noise - if the wheel is gripping a bit then there will be a considerable snatching force on he front suspension. On cars with a conventional system presumably there will also be electric pump noise as well.

Post by **CitroJim** » 25 Jul 2007, 18:18

It is interesting the you other Xantia owners report you can feel the ABS working and yet I never have in either of mine.

Now, either I'm not braking really hard and not really bringing the ABS right into operation, quite possible as I'm a very gentle driver and my definition of an emergency stop may not be the same as others or it could be this:

The only times I've really gone for an emergency stop is when both cars had springs in their brake pedals. Perhaps the spring absorbs all the pulses or is it that I'm usually wearing heavy work boots when driving

I'll go do a test stop in the Activa over the next few days and see as the Activa now has the "solid spring" fitted in the brake pedal.

Homer · Post by **Homer** » 25 Jul 2007, 18:24

citrojim wrote:It is interesting the you other Xantia owners report you can feel the ABS working and yet I never have in either of mine.

I could never feel it activating on a dry or even a wet road, and I'm pretty sure I provoked it enough. Certainly took a bit of getting used to the (non ABS) BX after driving the Xantia.

The only times I did notice it were if I got one wheel on mud, in which case it was more a shuddering through the steering than the pedal. And on black ice at low speed when I could definitely feel it through the pedal.

Xaccers · Post by **Xaccers** » 25 Jul 2007, 18:48

Jim, you'll have to take Dex out and do an emergency stop, on the 3 Xantia's I've owned, all gave feed back from the ABS.

Mandrake · Post by **Mandrake** » 25 Jul 2007, 21:14

I can feel the ABS working on the pedal on mine - and hear it too.

Regards,
Simon

Ross_K · Post by **Ross_K** » 25 Jul 2007, 21:47

I got to test mine for the first time at the weekend when a granny stepped into the road in front of me. There's definitely a judder from the brake pedal when the ABS kicks in...

frenchcarnut · Post by **frenchcarnut** » 26 Jul 2007, 19:07

Well it was wet today and so great opp. to test brakes. And the C5 reacted like the Xantia used to so no change there then.

Thanks for everyones responses. I now know that I'm NOT going completely mad