ABS Sensor

[Master]

Had a problem getting a broken & seized ABS sensor out of the hub...An hour later..Its out..Put in the new one checked the dash ABS fault light has gone
out..Horray...Took the car for a spin & although they worked the brakes give off a grinding noise the sensation through the pedal was that of the ABS working as it should but with the grinding noise as if 2 heavy metals were rubbing against each other....I never touched any other part of the braking syatem ...Its not the dust plate rubbing against the disc ..different type of noise ..Im thinking has some of the sensor broken off & fallen into the hub...Do these symptoms sound familier to anyone

[Jakg]

The grinding noise is the ABS system working because it thinks one of your wheels has locked up under braking - i.e. it's not reading a wheel speed correctly - the sensor isn't working right.

It's not actually a grinding noise from the brakes, don't worry, but you do need to fix it - lots of info on the forum about it.


Typical causes include - bad sensor, not installed far enough (corrosion), not installed far enough (poor quality sensor, should be closer to the hub, poor tolerance), damage to wheel bearing during removal of old sensor.

[Master]

Originally Posted by Jakg

The grinding noise is the ABS system working because it thinks one of your wheels has locked up under braking - i.e. it's not reading a wheel speed correctly - the sensor isn't working right.

It's not actually a grinding noise from the brakes, don't worry, but you do need to fix it - lots of info on the forum about it.


Typical causes include - bad sensor, not installed far enough (corrosion), not installed far enough (poor quality sensor, should be closer to the hub, poor tolerance), damage to wheel bearing during removal of old sensor.

Surely if the new sensor has turned off the ABS warning light then it would be working as it should & be fault free...The noise sounds nothing like the ABS sensor activating which is why im thinking rubish in the hub...Tomorrow i will remove it & see if the noise is still there

[HarryM1BYT]

If the noise is present ALL the time the wheel is rotating, then something as fallen in or a backplate or similar is rubbing. If only when you press the pedal then a pad is down to the metal. If you feel a vibration at the pedal and a noise, that is the ABS kicking in.

Likely the latter is due to your sensor missing pulses and assuing a wheel has stopped rotating. Often due to the sensor being fitted to far out from the rotor in the hub. It will not bring the ABS warning light on.

[Jakg]

Originally Posted by Master

Surely if the new sensor has turned off the ABS warning light then it would be working as it should & be fault free

The ABS warning light means "no signal from the sensor, open circuit" (or similar).

If the ABS sensor has a proper resistance, but doesn't pick properly pick up all the pulses on the wheel, then you'll have the problem your experiencing.

Originally Posted by Master

The noise sounds nothing like the ABS sensor activating which is why im thinking rubish in the hub...Tomorrow i will remove it & see if the noise is still there

It's not the sensor making the noise - it's the ABS unit opening and closing valves etc.

Try taking out the ABS fuse and trying again if you still need convincing

[Master]

Originally Posted by HarryM1BYT

If the noise is present ALL the time the wheel is rotating, then something as fallen in or a backplate or similar is rubbing. If only when you press the pedal then a pad is down to the metal. If you feel a vibration at the pedal and a noise, that is the ABS kicking in.

Likely the latter is due to your sensor missing pulses and assuing a wheel has stopped rotating. Often due to the sensor being fitted to far out from the rotor in the hub. It will not bring the ABS warning light on.

Brian..( Marinabrian ) told me this could happen & that in the past has filed off a bit of the collar so that the sensor sits further down & closer to the rota

[Mike Noc]

Could be a slightly too big air gap, or the magnetic reluctor has been damaged getting the old one out.

Courtesy of French Mike you can check all the ABS sensors and magnetic reluctors in the wheel bearings using a voltmeter.

The signal voltage changes from 1.7V to 0.7V as each magnetic segment passes the sensor, so jack the wheel up and slowly rotate it marking any failures on the tyre wall with chalk. If the sensor you have changed checks out then do the same test on the other wheels.

If the failures are in the same place each revolution then likely a damaged reluctor, and if in random places suspect the sensor or possibly a slightly too big air gap.

Here is a front hub being tested prior to fitting. I use an extension cable made up from some old speaker wire and ABS plug and socket which saves pinning through the ABS cables. It also doubles up to allow any sensor to be plugged in to the OSF so that the speedometer can be used as a diagnostic.

[IMG][/IMG]

[EastPete]

The reluctor is within the wheel bearing - correct ? I have just stripped my front hubs, and was quite brutal getting the old ABS sensors out. I guess it does not matter as I am pressing in new bearings (hopefully later today). My main concern is getting the new sensors in place without doing any damage to the new sensors or the new bearings - they seem a very tight fit in the holes in the hub.

Pete

[HarryM1BYT]

Originally Posted by EastPete

The reluctor is within the wheel bearing - correct ? I have just stripped my front hubs, and was quite brutal getting the old ABS sensors out. I guess it does not matter as I am pressing in new bearings (hopefully later today). My main concern is getting the new sensors in place without doing any damage to the new sensors or the new bearings - they seem a very tight fit in the holes in the hub.

Pete

The reluctor/ rotor is within the wheel bearing.

Maybe source a suitably sized drill to just clean out the rust in the hole, so it slides in more easily - the sensor are quite easily damaged.

I would also be inclined to accurately measure the distance between the mounting face of the hole and the rotor, then measure how far in the sensor goes into the hole - just for future reference and maybe post it on here.

No one seems to have bothered doing this and the air gap between sensor and rotor seems to be quite critical for proper operation.

[EastPete]

Originally Posted by HarryM1BYT

The reluctor/ rotor is within the wheel bearing.

Maybe source a suitably sized drill to just clean out the rust in the hole, so it slides in more easily - the sensor are quite easily damaged.

I would also be inclined to accurately measure the distance between the mounting face of the hole and the rotor, then measure how far in the sensor goes into the hole - just for future reference and maybe post it on here.

No one seems to have bothered doing this and the air gap between sensor and rotor seems to be quite critical for proper operation.

Thanks Harry - I'll try to do the measurements and possibly post some pictures. I have two new sensors - one after-market from DMGRS, and one genuine Rover one from Rimmers - from a first quick look, the Rover one is a bit slimmer and does seem to start to go into the hole without too much force - the DMGRS will need a gentle trim round the sides to get it to fit, I think. Some folks on here also suggest filing down the metal sleeve slightly on the bolt hole on the retaining arm of the sensor for the after market sensors, to make sure the tip of the sensor is positioned properly over the reluctor/rotor - is this a good idea ?

Thanks for all the advice.

Pete