ABS Sensor Grease

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Here is part of a GM TSB on ABS false activation "Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in the General Information sub-section of the Service Manual (SI Document ID #899664). Disconnect both the front wheel speed sensor (WSS) connectors at the frame and harness. Place a Digital Volt Meter (DVM) across the terminals of each WSS connector. Rotate the wheel clockwise approximately one revolution per second. The minimum reading should be at least 350 ACmV's. If the reading is less than 350 ACmV's, remove the wheel speed sensor. Refer to the applicable Wheel Speed Sensor Replacement procedure in the ABS sub-section of the Service Manual. Plug the WSS bore in order to prevent debris from falling into the hub during service. Clean the WSS mounting surface on the hub to remove any rust or corrosion using a wire brush, or equivalent. Important Make sure that the sensor sits flat on the hub. Check the sensor flange against a straight edge to ensure flatness. If the sensor flange is distorted, replace the sensor. Apply a thin layer of bearing grease to the hub surface and sensor O-ring prior to sensor installation. Use ONLY Wheel Bearing Lubricant, P/N 01051344 (Canadian P/N 993037). Install either the original sensor or a new one in the hub. Ensure that the sensor is seated flush against the hub. Refer to the applicable Wheel Speed Sensor Replacement procedure in the ABS sub-section of the Service Manual. Place the DVM across the sensor terminals and recheck the voltage while rotating the wheel. The voltage should now read at least 350 ACmV's" Note that GM asks for wheel bearing grease to be used when inserting the ABS ssensor into its mounting hole. Wabco also asks for a mineral-based lubricant to be used with its ABS wheel speed sensors. I have been ignoring Wabco's suggestion and have been using dielectric grease on the medium duty trucks at work. Yesterday I came across the GM TSB that I posted above and now I am really curious as to why a mineral-based lubricant is specifically called for for ABS sensors.
 
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George7941

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Chassis grease is even more tacky and resists water wash-out well, better than wheel-bearing grease. So, why did they not call for chassis grease? I have a five-gallon pail that I had bought chassis grease in and I washed it out to reuse as a container and that is when I realised how sticky chassis grease is. It took me half an hour to get the pail clean and if I had known how sticky chassis grease is, I would have just thrown away the pail.
 

George7941

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Originally Posted By: benjamming
Which is less expensive?
Considering the tiny amounbt of grease used to install the sensor, cost isn't a factor here,IMO.
 

George7941

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Originally Posted By: Kestas
The wrong type of grease can attack the copper windings in the sensor, rendering the sensor useless.
The sensor windings are inside the sensor casing and the casing looks like stainless steel(non-magnetic). The grease will have to eat thru stainless steel before it can get at the copper. Surely di-electric grease is pretty inert and is not going to attack stainless steel. I don't believe any of us has come up with an explanation for this requirement for mineral-based grease. I will e-mail Wabco and see if I can get an explanation.
 
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Googling a little, I found this answer in weldingweb.com, which looks like the grease is recommended in order to keep the socket from rusting, not because it's made from unobtainium: GM found that it's not always the sensor that is the problem. Rust builds up between the sensor and the hub causing the sensor to lift slightly. This increases the air gap between the sensor and the tone ring causing the low speed activation you've described. GM had us pull the sensors, stuff cloth down the sensor hole, and clean the hub area where the sensor mounts. Once all corrosion was gone we'd apply a type of rust converter to the hub, standard chassis grease on the sensor and reinstall it. This fixes them completely.
 
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northern Alabama
Originally Posted By: George7941
Originally Posted By: benjamming
Which is less expensive?
Considering the tiny amounbt of grease used to install the sensor, cost isn't a factor here,IMO.
I wasn't speaking about this one instance but rather a possible reason for the lubricant choice. They may be passing along what they use at the factory, & it will be based (partially) upon cost.
 
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