Entrapment. My top fear, right after heights and too thick (or thin, for that matter) a glaze on my creme brulee. No matter what I do to ensure my car is properly lifted and secured, there's a nagging fear in my head my repair work will end tragically, where my last sight is the under-body of a Ford Freestyle before my demise; at least I will have the happiest widow in the tri-county area.
Lifting the rear of the Freestyle requires more forethought, because there's not a good lift point aft of the front door where I can fit a jack and then a jack stand to bear the weight while I'm working. To lift the car, I jacked the front enough to lift the rear tire off of the ground and then placed a jack stand at the rear of the car on the unibody rails where one would put a scissor jack whilst doing a road-side tire swap-out.
Once the wheel was off, the sensor was nicely exposed and I had (just!) enough clearance to do what I needed to be done.
Locating the Sensor
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| Path of sensor wire from knuckle |
Like the front sensor, this sensor was stuck in the steering knuckle, followed a suspension member and connected with a two-wire socket to the wire heading back to the ABS unit.
At the wheel hub, I tried disconnecting the sensor and pulling, then prying. Unlike the front wheel, I didn't have the expectation that I could remove the sensor as it was installed, so I moved from the "try to pull it out" to "just break the top off" very quickly. Eventually, I broke the top of the sensor from stem, leaving the drill as my next alternative.
Starting with a small bit, I drilled into the plastic because of my position under the car, didn't pay attention and didn't keep the bit straight, whereupon SNAP, I broke the bit. No problem, I would switch to a bigger bit and eventually knock the small bit out. But... larger bits started to bind on the remnants of the broken bit and it became clear a new approach would be in order.
In a general sense, ABS sensors works through the Hall effect (thanks Edwin!), a change in voltage due to the proximity of a magnet. In the Freestyle, ABS sensors contain a little bit of circuitry along with the sensor report back the position of the wheel relative to some material in the axle that, when passing by a magnet, reports some change in voltage. Given the sensor reads something in the axle (or wheel hub), I should be able to remove the wheel hub to get to the location of the top of the sensor in the wheel knuckle. From that direction, I could remove the remaining part of the sensor. To access the hub, I would need to remove the wheel nut and brakes. Let's start with the wheel nut.
Removing the wheel hub
Removing a wheel nut is done by putting the car on the ground and using its weight to counter act the force of the breaker bar. If the wheel were in the air, it would just spin with the force applied. I dropped the wheel to the ground, got my 32MM wheel hub socket (which, incidentally, is the same size hub nut on my minivan, saving me from buying it) on the end of my breaker bar and removed the wheel nut. This was surprisingly easy, considering a wheel hub nut is usually under +100 ft/lbs of force.
Wheel nut off, brakes were then removed -- read-up on the rear brake replacement for the details on how to do this, no need to repeat it here. Then four 10MM bolts were unwound from the rear of the wheel knuckle with the aid of a smaller breaker bar. This worked a little to well, such that it looked like these parts were replaced once already. Once removed, the sensor made itself apparent and a 3/4 socket extension and a tap with a mallet removed the offending part.
As mentioned, since the bearing was removed so easily, I was suspicious somebody replaced this part already. Examining the part, it looks to be a Mevotech 512300. Look at the slots in the plate over the bearing parts, this isn't found on Timken or Moog parts. Also, looking a the condition of the bolt, I didn't feel like I broke any thread lock. Plus the bolt head looks like it was worked before, so I'm voting for this being a replacement part.
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| Wheel hub and one of the bolts |
The condition the wheel knuckle was a bit dirty. In my Puritan thinking, clean things work better. With a shop rag and wire brush, I removed as much of the dirt and grime as possible. Once clean, everything went back together again.
Back where I started
As expected, after clearing the codes by disconnecting the battery for 10 minutes, they all returned. It looks more like a wiring problem or a failed ABS unit, which will require a different tact to fix.
