Audi A4 Avant (1998) ABS Problem

[Avant Agro]

Hi all, this is my first post so be kind!
I have an A4 Avant 1998 1.8SE 20V manual.
I recently replaced the rear discs, pads, wheel bearings and ABS sensor rings, since then I have noticed a strange fault. When braking from slow speeds the car slows perfectly normally and just before it comes to a stop the brake pedal move down and then up (about 1/2 an inch) and makes a strange sound (too difficult to describe).
I purchased an OBD II cable and downloaded the latest VAG-COM software, got it all connected but it shows no ABS faults. The ABS light is not on at present, but did come on briefly during a 70mph plus motorway journey.
I'm running out of ideas, i've cleaned all the ABS sensors, blead the whole braking system, i'm guessing the ABS light needs to be on before VAG-COM can display the fault.
Any Ideas anyone?
Cheers

 

[shineydave]

my mate has exactly the same fault on his S4. we've put it down to an abs sensor being slightly too far out from the ring so it's not detecting correctly and thinks the wheel is skidding and so operates the abs, that's the vibration and oscillating sound you can hear.

we tried logging the sensors with vag-com but it disconnects from the controller as soon as you set off so we're no closer to identifying which sensor it is.

i've heard many other explainations for this too, such as worn wheel bearings allowing the wheel to run off-centre or different makes of tyre with different rolling radii causing the abs to kick in. might be worth checking the tyres and tread depths are all similar first then start looking at the sensors since working on them seems to have created the issue.

 

[Avant Agro]

A big thank you for your reply, your theory on the ABS sensor being too far out from the ring sounds spot on, I replaced the rear discs with pattern ones (cheapskate!) and its very likely that the sensor rings are now in a slightly different position to the originals. I'll attempt to bring the sensors closer to see if that works.

Wheel bearings are all good, tyres all have around 5mm, i'll check the pressures.

Again thanks for your ideas, i'll let you know how I get on.

Cheers

Paul

 

[Sebastian]

Many ABS control modules interrupt the diagnostic session at speeds higher than 20 km/h, so I suggest logging these at low speeds or while having the wheel lifted. Suggestion would be to drive until the warning light comes back, then there should be a fault stored again.

 

[Avant Agro]

Hi Sebastian, thanks for your reply, as I mentioned i'm a recent convert to car diagnostics, i'm impressed so far but my lack of knowledge is a barrier!
I have been running the ABS diagnostics with the car stationary with the wheels on the ground! Can you confirm that I should re-run the diagnostics but keep the speed below 20 km/h. I won't be at all offended if you treat me as an idiot, i'm use to it.

 

[Sebastian]

Yes, this is what you should do. Log the test drive and make sure there are no gaps/jumps in the values - this should be the best way to figure what's going on.

 

[Barbra (female Mechanic)]

Hi all, this is my first post so be kind!
I have an A4 Avant 1998 1.8SE 20V manual.
I recently replaced the rear discs, pads, wheel bearings and ABS sensor rings, since then I have noticed a strange fault. When braking from slow speeds the car slows perfectly normally and just before it comes to a stop the brake pedal move down and then up (about 1/2 an inch) and makes a strange sound (too difficult to describe).
I purchased an OBD II cable and downloaded the latest VAG-COM software, got it all connected but it shows no ABS faults. The ABS light is not on at present, but did come on briefly during a 70mph plus motorway journey.
I'm running out of ideas, i've cleaned all the ABS sensors, blead the whole braking system, i'm guessing the ABS light needs to be on before VAG-COM can display the fault.
Any Ideas anyone?
Cheers

Would just like to say Dave was spot on I had the same problen With an A 1997 A4 and it turned out to be the ABS sensor was not firmly pushed home into place,
Regards Barbra