| I took the wheels off my MX5 1.8iS (1997) for the first time this weekend (not had it long!) I noticed at the rear that on each side inboard of the brakes is a toothed wheel with what looks like some sort of sensor pointing at it. I assume that this is a detector for the ABS. Am I right? and if so what is the equivalent device at the front? or does it only detect the rear wheels locking? It certainly does work as I did a little test a while ago on an icy car park just to see what it felt like. (1/00) |
| There is a sensor on all four wheels. But normally there are only three channels of "drive", so the rear wheels are released at the same time, whereas the two fronts are independent. (1/00) |
| Yes ABS sensor wheels .. it counts the teeth going past and hence knows wheel speed/deceleration levels. The front ones are on the hub between the disc and the upright .. follow the wire attached to the shock absorber. .. and on another ABS car I have seen failures because the tooth wheel grew with rust so much that it hit the sensor and hence destroyed it .. so a coating of waxoyl or similar would be a good idea for older cars after cleaning out the teeth. (1/00) |
| I had an intermittent ABS fault light and took the car to the dealer. They hooked up a diagnostic system and knew exactly which toothed wheel to blather with brake cleaner. Next time I'll hit them all with brake cleaner first. (1/00) |
| That won't be a problem on the MX-5, because they are made from plastic. I had a good look at the underside of my 5 before I took delivery, and gave these toothed wheels a good investigation when they were shiney and new. (1/00) |
| .. they may be plastic coated but they are steel if they use conventional induction pickup types (the sensor) .. this method is cheap and reliable but any plastic sensor is going to be principal optical which don't survive with dirt. (1/00) |
| Went for a short run this morning and was aware the the ABS warning light was on. When I parked and turned off the ignition I could hear a vibration coming from indide of the engin compartment - when I looked the ABS unit was buzzing and vibrating (I guess this was the ABS unit - where the washer fluid reservoir is on the standard model). It even does it with the engin off and the ignition key out! I guess this is not good news - but just how bad is it? (12/00) |
| You can always pull the relay for the ABS which may stop the buzzing until you find out what the problem is, fluid level perhaps ? This is what I had to do in my Rover 620 to get reset the unit and get the warning lamp to go off anyway. I always tested the ABS on loose surface afterwards though to double check all was ok. (12/00) |
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It even does it with the engin off and the ignition key out! Really? Weird. Might be worth pulling the ABS relay to see if this clears the condition. Most ABS faults are due to dirty sensors - usually some brake cleaner on the notched wheel fixes it. (12/00) |
| I disconnected the relay as sugested but the vibration started as soon as I reconnected. I'm taking to my friendly Mazda dealer in the morning to let them sort it out.... Which brings me to my second question (and I'm sorry if this is old hat) I have asked the garage to do my 84 month service while they have the car. As you may remember, I recently changed the plugs, leads and installed a K&N filter so I don't need that stuff looking at, however, I had a major lub job 6000m/6 months back does that need doing again? (12/00) |
| Just talked to the garage who were looking in to the strange case of the oscillating ABS unit, and, as some or you suspected, the problem was a dodgie sensor in one of the wheels and will be covered by the momentum warranty. (12/00) |
| Was the sensor faulty or was it all just a bit dirty? (12/00) |