ABS brakes

Anacrusis

Does anyone know about ABS problems? My car has a problem which is caused by one of the brake discs having some of the cogs missing. The symptoms are that when using the brakes for the first 5 mins of driving there is a graunching or honking noise.

At first I had the brake pads changed, which didn't help (because it wasn't the problem!) and that garage couldn't find any problems.

Later I needed part of the exhaust changing, I went to a different garage, and they identified the ABS problem. They said that these discs would need changing before the MOT but that the car wasn't dangerous.

Today I've been back to the second garage with the power steering, which they said only needed more fluid and now seems fine. BUT the mechanic (a different one from last time) said that now half the cogs are missing, and not only is it very dangerous to drive, but that it would be very dangerous to drive with only one missing... so I'm left a bit confused...

Does anyone know:

Whether my car might be dangerous to drvie or not?!

If these cogs are being worn away, is there another underlying problem?

Why my ABS warning light hasn't come on??

Gloomendoom

Does your abs light come on when you first start the car and then go out, or does it not come on at all?

custardy

sounds to me lie you had a non ABS part added that doesnt have the 'cog' for the ABS sensor to read,or that part is broken
so the ABS ECU is flagging a fault
most likely it means you have no ABS,though it could posibly lead to the ABS working incorrectly which could be worse
this isnt really something to risk nor diagnose over the net

Anacrusis

The ABS light comes on and then goes out, which should mean it's ok(!!)

I know nothing about cars but I believe from what the mechanics have told me that there is something wrong with the ABS. I think I'm worried by the totally different reactions of the two mechanics to the same problem, and also that there is some other problem causing the discs to get the cog bits worn away...

Custady, what does ECU mean?

harveybobbles

if one, or some of the teeth are missing then the ABS sensor will give a false reading.

MX5huggy

What actually happens when you use the ABS?

Gloomendoom

ABS systems fail safe so the braking system will just act like a car with no ABS. However, it is odd that the system isn't seeing such an apparently obvious fault.

As has been said, what happens when you try to get the ABS to work?

(Best done on a long, wide, straight road with nobody else about.)

Silk

Ok first of all the "cogs" in question will be the Reluctor Rings which are a ring with teeth shrunk onto the driveshaft if teeth are missing it gives false readings to the ABS.

The problem with missing teeth is that the ECU counts the teeth rotating speed on each wheel and kicks in the ABS to compensate the different wheel speeds.

It will think the one with missing teeth is going slower which in fact is not happening

It's not the end of the world getting them replaced by a decent garage

Anacrusis

I'm a new driver (bear with me!) I think I might not have used the ABS - how fast would I have to drive + stop to test it? Any tips how to do it safely should it fail??!

I drive really carefully but drive fast on fast roads obviously... I think it must be dangerous that the ABS might fail if I'm going very fast + need to brake? So probably should get it sorted ASAP!

Silk

If they are correct and there are teeth missing it won't work properly ...end of story there is no need to test it

If a car is fitted with ABS you will be using it all the time because it's there working away in the background....it will only kick in under hard braking ...which is when you need it most and when you need to rely on it.
Normal braking under normal speeds you won't notice that it's there

boyse7en

If a car is fitted with ABS you will be using it all the time because it's there working away in the background....it will only kick in under hard braking ...which is when you need it most and when you need to rely on it.
Normal braking under normal speeds you won't notice that it's there

ABS doesn't work all the time. It only operates when it senses that one or more of the wheels has locked up, and the car is going faster than its threshold speed (the ABS has to stop operating below a certain speed, otherwise you would never come to a halt)

If teeth are missing from the reluctor ring, then the ring will need replacing (not a massive job). Why the teeth are missing would also need looking into, as they may have been hitting part of the hub assembly or the ABS sensor.

Replacing the brake discs will not repair the teeth, as they are a separate part (although the discs may need replacing just due to normal wear).

The 'honking' noise is also unlikely to be anything to do with the teeth missing from the ring, but could be due to worn discs, pads or a missing anti-rattle shim or lack of copper grease on the back of the pads.