Hi all

Yesterday, I was approaching a roundabout at normal roundabout approaching speed, and pressed the brake pedal to begin to slow. About two to three seconds after I started braking, the car went over a relatively significant bump in the road, immediately after which the anti-lock-brakes started going absolutely mental (ie working the whole time as if I was on ice or something). I released the brakes and pressed them again firmly, after which they worked fine; but the brake pedal went a long, long way down before anything happened.

I then found a quiet stretch of road and did some hard braking from ~ 50mph.

The first time, I had similar symptoms to before - the anti lock brakes were working quite a lot.

After a couple more it started to get better, and eventually the firmed up again (and the brake pedal stopped going quite so far down)

I had exactly the same symptoms with my previous fabia (1.9SDI classic) when I went over bumps whilst braking.

a) Why does it do this?

Is there a way to prevent it from happening?

c) Am I to be concerned about the behaviour of the brakes?

well it does it, because when braking, the friction of the tyre on the road is stopping it from locking, go over a bump (or wet metal grate ect) and the wheel will try to lock as the friction will go right down as the wheel is lifted into the air (you could have a knackered shocker, worth doing the "bounce" test, or looking for leakes on the shocks...) and the abs will cut in to stop it locking.....

should right itself though, as soon as its over the bump, and carry on braking normally, which is why I would wonder about the shocks, if the shocks are knackered, the wheel will keep bouncing, and the abs will keep operating!

only thing I can think of for explaining their behavior....

But the thing is when the ABS does kick it - it will continue to operate until the pedal is released. Regardless of of the road and tyre adhesion. I've found this out by doing a few tests - simply because I also get this problem. A junction near my house has a nasty pot hole in the road - when approaching the junction at say 30mph, hitting the hole under breaking will often unsettle the car and activate the ABS. It carries on until either the car stops or I release the pedal and re-press.

I don't think what your experiencing is really a fault - more a case of a very over-zealous ABS system on the Furby. I'm wondering if it can be turned down through the ECU and if so I am tempted to speak to the garage on the next service - because as far as I am concerned the ABS is far, far too premature and envasive. Especially for spirited driving.

I did do a quick search after I posted the thread (I know I should've done it before but time wasn't permitting...) and uncovered a couple of threads where such behaviour has almost caused an accident...

The best way to avoid it is to make sure that if you're going to brake hard, the road is dry, level and in good condition as these are the best conditions for stopping the car. Anything less than that and you'll want to either build up the braking earlier or back off as you approach the wet drain cover, etc.

You might also want to "hint" at the brakes, ie gently apply them, to push the fluid to all 4 corners of the car before using them in anger. This then means that all the calipers are squeezing at the same time and with the same pressure per wheel so you brake in a nice straight line.

Chris

This then means that all the calipers are squeezing at the same time

Chris

Forgive me for being what is quite possibly extremely naive, but surely car manufacturers have got braking systems to the point where that is the case automatically?