ABS Noise - RR Engine

[Steve]

Another ABS fault. This time when driving there is a hissing/whooshing noise coming from the ABS pump area. When braking, the car squirms and you can feel the ABS through the brake pedal. Sometimes when you come to a stop you hear a 'boing' type noise.

Previously the ABS light came on after 25mph or thereabouts. I've cleaned all the sensors and the teeth and the abs light has gone away. Car drives fine without the strange noise and brakes normal when ABS is switched off.

[quattrodave]

In my experience problems at low speeds (less than 10mph) when you can sometimes just feel the ABS kicking in for a split second are usually associated with bad reads from a sensor/sensors possibly caused by dirty rings or incorrect air gap between sensor and ABS ring.

Typically they occur on damp surfaces or when the wheels are not quite in the straight ahead position.

Just about every Audi I've owned over the past 30 years has suffered in this way at some point in its life. Cleaning sensors and ABS rings and making sure the sensor to ring air gap is correct usually fixes it for me.

Might not be your problem but worth a check

[sinbin5t]

I had all those things on a B4 coupe, one of the rings had moved out of place slightly and when back in place it all stopped.

[Steve]

Originally Posted by quattrodave

In my experience problems at low speeds (less than 10mph) when you can sometimes just feel the ABS kicking in for a split second are usually associated with bad reads from a sensor/sensors possibly caused by dirty rings or incorrect air gap between sensor and ABS ring.

Typically they occur on damp surfaces or when the wheels are not quite in the straight ahead position.

Just about every Audi I've owned over the past 30 years has suffered in this way at some point in its life. Cleaning sensors and ABS rings and making sure the sensor to ring air gap is correct usually fixes it for me.

Might not be your problem but worth a check

I backed all the sensors off and the noise stopped. I've tried setting the gap several times and this results in the ABS kicking in at various speeds when braking.

What is the air gap meant to be set at?

[QuattroBird]

On the front of the sensors should be a white push-on cap where there is a slot for the sensor. Either side of this slot will be sacrificial brush teeth which auto sets the gap and these teeth will break off by the toothed pick-up ring on the drive shaft which prevents the sensor making contact with teeth.
437927809 Is part ref pop into search engine.
I did not set mine properly initially at rebuild and had some weird abs sounds and pedal feeling. Like relay was firing. Once pushed in and locked went away.

[Groundhog]

Here’s my four pennies worth. In my many many years of working on Quattro’s most ABS faults could be fixed by resetting the sensors. Your fault is screaming air gap problem. In my opinion ( and following Audi’s advice) new sensor caps should be used each and every time a linked component is disturbed. The way I did it was to put a new cap on the sensor push it in till it touched the rotor, spin the wheel half(ish) a turn and while still keeping pressure on the sensor nip the bolt up. 99 times out of a hundred this works every time. If new caps are unavailable or you want a quicker fix then it is possible to measure the individual frequencies of the senders and adjust accordingly. There are different methods to do this and it largely depends on what equipment you have access to, if you google ‘ testing a ABS sender’ the different ways can be found and explained better than I can here, a multimeter is a minimal requirement though. I have very occasionally come across broken wires, particularly where they are clamped to body work but this would show very readily using test equipment.

[Steve]

Originally Posted by Groundhog

Here’s my four pennies worth. In my many many years of working on Quattro’s most ABS faults could be fixed by resetting the sensors. Your fault is screaming air gap problem. In my opinion ( and following Audi’s advice) new sensor caps should be used each and every time a linked component is disturbed. The way I did it was to put a new cap on the sensor push it in till it touched the rotor, spin the wheel half(ish) a turn and while still keeping pressure on the sensor nip the bolt up. 99 times out of a hundred this works every time. If new caps are unavailable or you want a quicker fix then it is possible to measure the individual frequencies of the senders and adjust accordingly. There are different methods to do this and it largely depends on what equipment you have access to, if you google ‘ testing a ABS sender’ the different ways can be found and explained better than I can here, a multimeter is a minimal requirement though. I have very occasionally come across broken wires, particularly where they are clamped to body work but this would show very readily using test equipment.

Well done you.

New abs caps fitted and away we go.

Thank you very much.

PS Thinking of investing in an oscilloscope as well so I can set the abs up without having to buy new caps, although I did take some measurements so I now know what the sweet spot is.

[urquattr085]

Originally Posted by Steve

Thinking of investing in an oscilloscope as well so I can set the abs up without having to buy new caps

I can highly recommend it.

It's great for checking which corner is giving you problems, without having to pull anything apart, just jack up a wheel, plug the scope into the sensor connector and give it a spin

Pleased you got it sorted Steve