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D2 A8/S8 (1997 - 2003)
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I would vote he found the issue
Posted by: AUTO-UNION.US (6318) on 2017-11-13 23:42:24
In Reply to: I would hesitate to call it "FIXED". You certainly got a good troubleshooting data point, though. posted by Dave Doolittle on 2017-11-13 23:02:16

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Audi 5000s and early 100's had an allen bolt that held the ABS sensor in a position that put the magnetic switch in the sensor at 90 degrees to the teeth of the reluctor which gave it its' optimal occassion to trigger on each tooth. In the early 90's Audi eliminated the allen bolt and instead incorporated a sleeve that put friction on the sensor and held it in whatever position it was put on the assembly line. We never saw an issue with it unless someone who didn't know what they were doing [mostly while fixing a torn cv boot or cv axle] moved the magnetic switch from its' optimal position and it wouldn't trigger especially if metal had accumulated on the face of the sensor due to magnetism. It is easy to demonstrate if you have a spare sensor around. Hook it up to an ohm meter and run the steel shaft of a screw driver across the face. If you are running the blade perpendicular to the magnetic switch, you will get a reading after each swipe; but if you are parellel to the switch, you will not get a switch every time.
The process is so precise, the manufactures including Audi now frequently use the ABS system to determine tire pressure instead of having the pickup in the valve stem. If the tire has less air than it is supposed to have, the tire, wheel and reluctor travel at a minutly faster speed which is computed and transformed into tire pressure.
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All messages | Search Forums | Return to D2 A8/S8 (1997 - 2003)