brakes humming!

[falcoron]

Hi,
My rear wheel bearings where relaced after one of the inside ones collapsed.
When it went the abs warning light came on.
Ive replaced all rear wheel bearings and the light is now off and car is as it should be again. But (theres always a but) when im slowing down to a halt and pressing the brakes to final stop the last second (before i actually stop) there is a humming sound and i can feel vibration through the brake pedal. It dosent happen at any other time when braking, even when emergency braking, which i have tried, just when slowing down gradually to a stop. I have good disc's,pads, and fluid is fine. Never happened before bearings went and the car stops fine as it always has.
I would appreciate all or any advice.
I dont worry about anything else, but brakes!:aargh4:
Cheers
Ron

[scotty33]

This sounds like the ABS is modulating i.e detecting a locked wheel (in this case it is wrong so probably a sensor problem). A sensor may have been disturbed when the bearing collapsed, or during the repair?
The system needs all 4 sensors to be set the same distance from the toothed rings and for them to be 'sensing' each individual tooth/groove on the tone ring. If there is any debris stuck between the teeth this won't help, if the tone ring is damaged, eg chipped tooth or cracked = wide gap, this could also upset it. If you can't see anything wrong, and you know the sensor was removed/adjusted, try adjusting it's position.
If still no joy, the later cars may be able to store ABS fault codes so a scan could tell you what is wrong?

[falcoron]

This sounds like the ABS is modulating i.e detecting a locked wheel (in this case it is wrong so probably a sensor problem). A sensor may have been disturbed when the bearing collapsed, or during the repair?
The system needs all 4 sensors to be set the same distance from the toothed rings and for them to be 'sensing' each individual tooth/groove on the tone ring. If there is any debris stuck between the teeth this won't help, if the tone ring is damaged, eg chipped tooth or cracked = wide gap, this could also upset it. If you can't see anything wrong, and you know the sensor was removed/adjusted, try adjusting it's position.
If still no joy, the later cars may be able to store ABS fault codes so a scan could tell you what is wrong?

I did notice when replacing the rear bearings that one of the rear sensors had been touched by the sensor ring and had scored the sensor. How can i fix this? and how do i know what the distance between the disc and sensor should be. are they all the same for the 4 wheels?
thanks

[scotty33]

There may be a tool available from the dealer for setting this gap. Assuming the sensor is still effective but has been moved, you have nothing to lose by pushing it all the way in until it touches, then draw it away to leave a small gap.
There is a way of testing the sensor function with a multimeter, this involves spinning the wheels by hand, the signal strength should be equal, you can imagine, it is hard to match the speed at which the wheels are spun.
see first paragraphs on this link:

http://20v.org/brakprob.htm

And more, generic info here: http://www.sjmautotechnik.com/trouble_shooting/brake.html#ABS

[falcoron]

There may be a tool available from the dealer for setting this gap. Assuming the sensor is still effective but has been moved, you have nothing to lose by pushing it all the way in until it touches, then draw it away to leave a small gap.
There is a way of testing the sensor function with a multimeter, this involves spinning the wheels by hand, the signal strength should be equal, you can imagine, it is hard to match the speed at which the wheels are spun.
see first paragraphs on this link:

http://20v.org/brakprob.htm

And more, generic info here: http://www.sjmautotechnik.com/trouble_shooting/brake.html#ABS

Cheers Scotty,
The light went out when i replaced the bearings but this sound then appeared. from what i have read from your links i need to get it reset at the right distance.
The first link suggests that the sensor is too far away which would be right if the ring touched it after the bearing went south. Will try measuring the gaps all round and see if i can find the common didtance.
Cheers
Ron