ABS brakes

Silk

boyse7en wrote: »

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)

:rotfl::rotfl::rotfl:
Goodness I was trying to keep it simple so the OP could understand it

The ABS is constantly monitoring the wheel speeds hence why I said it was running in the background and why I said it kicks in under hard braking.

The ABS does not operate when it senses a wheel has locked up it operates when it senses a wheel is about to lock up ...it would be too late if it's locked up already.

I ruled out brake discs as the OP states that he had new pads fitted and would have thought the garage would have changed the discs if needed or at least advised them.
The OP mentions the discs when having exhaust fitted so assume it's standard Kwick Fit or similar operation working on the usual bonus stuff.

Missing teeth can be due to rust as well as fracture and a few symptoms include noise during braking at low speed

Gloomendoom

Anacrusis wrote: »

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!

It won't be any more dangerous than a car that doesn't have ABS and there are millions of those on the roads.

You can check it by slamming the brakes on hard. You don't need to be going very fast. You should hear a grinding sort of noise from the front and the brake pedal will vibrate. I recommend doing it on a straight and clear road though.

Oh, and look in the mirror before you try it.

flashg67

is it not possible that the missing teeth are normal - does the ABS not need one missing tooth per cog to 'know' when it's done a complete revolution? I'm not an ABS expert (before my time!) but the electro-magnetic sensor needs to have reference reading every rotation does it not?

Definately get it checked elsewhere. ABS is a sensitive system so ANY fault detected puts it into failsafe mode, switches the ABS off and put the warning light on, which apparently it currently isn't?

Could the graunching noise first thing not just be overnight rust being cleaned when the brakes are first used - I've had plenty of cars with that issue.

Silk

Gloomendoom wrote: »

It won't be any more dangerous than a car that doesn't have ABS and there are millions of those on the roads.

Strictly speaking that would only be true if the ABS had shut itself down or been turned off.
The problem with missing teeth is that the sensors count the number of teeth passing through every m/sec so it will think that the one with less teeth is slowing faster than the others and reduce pressure to compensate.

I'm guessing here that it's still active as the warning light has not come on and the symptoms described sounds like it is.

The mechanic has mentioned that half the teeth are missing and of course the more teeth that are missing the slower the sensors think the wheel is turning and the more pressure goes to the other side.....some systems even compensate front to rear pressures as well as side to side.

A malfunctioning ABS system thats active is far more dangerous than a car not fitted with ABS.

Anacrusis

Thanks for all the replies everyone, it's really helpfull.

I'm going to ring round a few garages tomorrow and ask for advice now I know a bit more about it.

I checked the ABS light today and it isn't coming on at all, I was wrong about that.

It was a kwik fit type garage (not kwik fit though) but I asked the mechanic to check out the noise when he did the exhaust.

Silk

Anacrusis wrote: »

I checked the ABS light today and it isn't coming on at all, I was wrong about that.

If the warning light does not come on when you turn on the ignition and there is a fault then it's a knocking bet that the bulb has been taken out to disguise the fact there is a fault.

You need to get the Reluctor Ring replaced ...new rings can usualy be fitted to the old cv joint although depends on make and model and of course some garages will want to replace it with a recon drive shaft rather than fit a new ring.

Gloomendoom

Most (all?) cars with ABS have a built in diagnostic system that will tell you exactly what problems you have. On some they can be accessed through the OBD port. On others (usually older) the fault codes can be read off a sequence of flashes from the ABS light.

If you have a bulb in it that is.

Silk

Gloomendoom wrote: »

Most (all?) cars with ABS have a built in diagnostic system that will tell you exactly what problems you have. On some they can be accessed through the OBD port. On others (usually older) the fault codes can be read off a sequence of flashes from the ABS light.

If you have a bulb in it that is.

Most faults yes but it's very rare to find a fault code for missing teeth on a Reluctor Ring