ABS operation - Page 2

tractor Dave · 18-05-19, 08:44 PM

Could it be the coolant after run pump you can hear?
I don't think any pump should be running on the abs when not activated. Try disconnecting the abs completely by removing the fuse or control box and see if that stops the noise.

BackintheFold · 18-05-19, 08:58 PM

Quote:

Originally Posted by tractor Dave

Could it be the coolant after run pump you can hear?
I don't think any pump should be running on the abs when not activated. Try disconnecting the abs completely by removing the fuse or control box and see if that stops the noise.

Too noisy for the after run pump.

If I switch ABS off, I get no noise so it does seem to be the ABS. I suppose I could get it tested then figure this out after.

tractor Dave · 18-05-19, 09:14 PM

I've been searching the S2 forum for you and similar issues have been faulty bomb or the servo. A conversion to Vac brakes is recommended and ditch the bomb! Not sure if you have sufficient space though. Alex on the S2 forum (error404) does a very good kit and will advise if you decide to go that route.

tractor Dave · 18-05-19, 09:24 PM

Or oil pressure switch at 23
https://audi.7zap.com/en/rdw/audi+qu...6/6/612-53005/

Also check you have good earth on the ABS pump (underneath on mine)

mikes2 · 18-05-19, 10:31 PM

if it's only happening at really slow speeds as you are coming to a stop, it's the ABS modulator making the noise.

BackintheFold · 19-05-19, 08:31 AM

I've been thinking more about this, in conjunction with comments and Thai site:
https://www.knowyourparts.com/techni...ator-problems/

I'm tending now towards sensor issues at low speeds making system think that a wheel is locked. The noise could be the valves opening and closing.
EDIT(AS per Mike above-ABS modulator)

At faster speeds the sensor outputs are more stable, so less likely to cause an issue.

Of course it's difficult to drive around in the private roads here at 40mph to confirm this, so I'll have to take a look at the rear sender teeth and the connections before trying to remove and clean the sensors themselves (last option!)

Off to Duxford now, so more in the week.

Edit:I'll test the bomb first because the first check is simple.
The interesting thing is the noise happens whether I'm braking or not, which (I think) only makes sense if the system is getting a bad signal from the sensors.
Generally, the noise happens when braking or not, but certainly more often when braking.
The noise doesn't seem to happen at higher (30mph) speeds, but does happen more often at lower speeds (less than 10), and also more often when braking-in particular braking to a stop.

Hanuman · 19-05-19, 10:38 AM

I get a similar effect at low speed with the V8, when coming to a halt, and especially when turning.

BackintheFold · 10-09-19, 11:51 AM

I've bought a £20 oscilloscope from eBay, so i can check the signals coming from each sensor-the re is NO WAY i'm prepared to remove any of them (and risk breaking them) until I know that that specific sensor is a problem!!

BackintheFold · 14-09-20, 09:00 AM

Re-starting this thread.
My rear left sensor is giving a bad signal, so will check it out before too long-hopefully by end of September.
The waveform showing on my oscilloscope is a square (ish) wave from three sensors, and a perfect sine wave from one.

I'm aiming my sights at the sine wave, on the basis that I have read that the output should be square on this system. I may remove the driveshaft to clean the ring, or i may try to remove the sensor and clean the ring through the hole, then re-set the sensor. I don't want to disturb the tracking so will have to see if i can remove the driveshaft without disturbing it, then decide what to do.

BackintheFold · 07-11-20, 02:31 PM

Finally got round to this.
Jacked car up, removed wheel. Sine wave output on oscilloscope
Undid Allen bolt locking plate very easily. Tapped sensor with a hammer twice. Turned hub and now got a rubbing sound.

Using fingers, grabbed back of sensor and tried pulling out and wiggling. Couldn’t see any movement but turning hub now resulted in No noise.
Also getting a square wave! Hurray!

Road test showed massive improvement, but on rare occasions on pulling up-even if not braking-I got a very brief pump type noise as before.
If I was guessing, I’d say the system is looking for a certain pressure from the system and when it doesn’t get it it uses a mechanical pump to increase the pressure. I know that is not right, but maybe it’s an indication of what’s happenings

In any event, I’m happy with it as it is.

Now I need to replace the rear pads which are looking a bit low. Hopefully a standard part andnot a gazillion pounds!

18-05-19, 10:31 PM	#15
mikes2 4 ring whore! Classic Audi Club Member Join Date: Nov 2007 Location: Polmont Posts: 2,617	if it's only happening at really slow speeds as you are coming to a stop, it's the ABS modulator making the noise. __________________ 1991 90 quattro 20v sport 1991 90 quattro

19-05-19, 08:31 AM	#16
BackintheFold Senior Member Classic Audi Club Member Join Date: Feb 2019 Location: Near an MB ur Quattro Posts: 1,171	I've been thinking more about this, in conjunction with comments and Thai site: https://www.knowyourparts.com/techni...ator-problems/ I'm tending now towards sensor issues at low speeds making system think that a wheel is locked. The noise could be the valves opening and closing. EDIT(AS per Mike above-ABS modulator) At faster speeds the sensor outputs are more stable, so less likely to cause an issue. Of course it's difficult to drive around in the private roads here at 40mph to confirm this, so I'll have to take a look at the rear sender teeth and the connections before trying to remove and clean the sensors themselves (last option!) Off to Duxford now, so more in the week. Edit:I'll test the bomb first because the first check is simple. The interesting thing is the noise happens whether I'm braking or not, which (I think) only makes sense if the system is getting a bad signal from the sensors. Generally, the noise happens when braking or not, but certainly more often when braking. The noise doesn't seem to happen at higher (30mph) speeds, but does happen more often at lower speeds (less than 10), and also more often when braking-in particular braking to a stop. Last edited by BackintheFold; 20-05-19 at 09:30 AM.

19-05-19, 10:38 AM	#17
Hanuman Trickster Classic Audi Club Member Join Date: May 2009 Location: Heckling from the cheap seats, Phnom Penh, KoW Posts: 7,006	I get a similar effect at low speed with the V8, when coming to a halt, and especially when turning. __________________ I wish they would keep the damned Chinese away now that I can go home, so that I can enjoy Fish amok and a draught Angkor

14-09-20, 09:00 AM	#19
BackintheFold Senior Member Classic Audi Club Member Join Date: Feb 2019 Location: Near an MB ur Quattro Posts: 1,171	Re-starting this thread. My rear left sensor is giving a bad signal, so will check it out before too long-hopefully by end of September. The waveform showing on my oscilloscope is a square (ish) wave from three sensors, and a perfect sine wave from one. I'm aiming my sights at the sine wave, on the basis that I have read that the output should be square on this system. I may remove the driveshaft to clean the ring, or i may try to remove the sensor and clean the ring through the hole, then re-set the sensor. I don't want to disturb the tracking so will have to see if i can remove the driveshaft without disturbing it, then decide what to do. __________________ 2006 A3 (daily drive) 1987 MB ur Last edited by BackintheFold; 14-09-20 at 10:22 AM.

07-11-20, 02:31 PM	#20
BackintheFold Senior Member Classic Audi Club Member Join Date: Feb 2019 Location: Near an MB ur Quattro Posts: 1,171	Finally got round to this. Jacked car up, removed wheel. Sine wave output on oscilloscope Undid Allen bolt locking plate very easily. Tapped sensor with a hammer twice. Turned hub and now got a rubbing sound. Using fingers, grabbed back of sensor and tried pulling out and wiggling. Couldn’t see any movement but turning hub now resulted in No noise. Also getting a square wave! Hurray! Road test showed massive improvement, but on rare occasions on pulling up-even if not braking-I got a very brief pump type noise as before. If I was guessing, I’d say the system is looking for a certain pressure from the system and when it doesn’t get it it uses a mechanical pump to increase the pressure. I know that is not right, but maybe it’s an indication of what’s happenings In any event, I’m happy with it as it is. Now I need to replace the rear pads which are looking a bit low. Hopefully a standard part andnot a gazillion pounds! __________________ 2006 A3 (daily drive) 1987 MB ur

18-05-19, 08:44 PM	#11
tractor Dave Senior Member Classic Audi Club Member Join Date: Apr 2018 Location: Wales Posts: 1,157	Could it be the coolant after run pump you can hear? I don't think any pump should be running on the abs when not activated. Try disconnecting the abs completely by removing the fuse or control box and see if that stops the noise.

18-05-19, 09:14 PM	#13
tractor Dave Senior Member Classic Audi Club Member Join Date: Apr 2018 Location: Wales Posts: 1,157	I've been searching the S2 forum for you and similar issues have been faulty bomb or the servo. A conversion to Vac brakes is recommended and ditch the bomb! Not sure if you have sufficient space though. Alex on the S2 forum (error404) does a very good kit and will advise if you decide to go that route.

18-05-19, 09:24 PM	#14
tractor Dave Senior Member Classic Audi Club Member Join Date: Apr 2018 Location: Wales Posts: 1,157	Or oil pressure switch at 23 https://audi.7zap.com/en/rdw/audi+qu...6/6/612-53005/ Also check you have good earth on the ABS pump (underneath on mine)

10-09-19, 11:51 AM	#18
BackintheFold Senior Member Classic Audi Club Member Join Date: Feb 2019 Location: Near an MB ur Quattro Posts: 1,171	I've bought a £20 oscilloscope from eBay, so i can check the signals coming from each sensor-the re is NO WAY i'm prepared to remove any of them (and risk breaking them) until I know that that specific sensor is a problem!!