Replacing a rear wheel speed sensor on r53. Not expected to be easy. It isn’t. No hold down bolt, got new one from dealer. No way sensor is coming out. Broken into pieces and dremeled almost out. Breaking the old one off reveals that the hold down bolt is not missing, it is snapped off flush.

I’m going at everything from the back, not pulling the brake or hub. After much careful grinding and vacuuming, the new sensor just about slides in. There’s about 1/4 inch left, but still stuff in the bottom of the hole. I suspect it’s the metallic remnant of the sensor and probably a bit more plastic. From videos, it looks like the sensor’s hole goes all the way through the hub carrier and the sensor rides on the back of the wheel bearing. The distance between the end of the sensor and the bearing is probably critical.

two questions:
1) as I attempt to drill out the remaining old sensor, do I have to be concerned about damaging the wheel bearing?
2) there’s no way I can drill out the broken sensor mounting bolt. Can I epoxy the tab of the new sensor?

 

1) Yes, When I did my front sensor, I masked off the drill bit so it was only as long as the sensor from the mounting flange to the end including the tip of the drill bit. If you drill past that length, you'll contact the magnetic ring on the wheel bearing and get a fault code.
2) You probably could, you'd have to be really **** about cleaning the flat where it mounts, just be careful not to get the epoxy into the hole where the sensor goes. BTW, I coated the outside of the sensor with high temperature grease before I installed it to keep the water out and make it easier to remove next time it fails.

 

1) I kind of thought that might be the case. I’m using a flat bottom grinder bit on my dremel, and I’ll lock it in so it can’t get to the ring. Hopefully.
2) worried about the epoxy spreading into the hole, too, and then I thought what the hell? If I take it out again, it’ll have to be destroyed anyway, so. A little glue down there - who cares? I’ll try and avoid that, though. And I’ve got some anti-seize compound to put on there. Would grease be better?

 

I considered Anti-Seize as well, but wanted to keep the water out and make rusting a negligible possibility, plus i was worried about the potential for the metal particles in the anti-seize confusing the sensor. That shouldn't really be an issue since anti-seize doesn't have any steel in it, just nickel, copper and non-ferrous materials. So do what you think works best.

 

Assuming my drilling goes well.

 

After careful drilling and spraying and swabbing, the wheel sensor would fit all the way into the hole. Without securing it, just a press fit, I set the car down and drove a few yards to see if the lights would go out. They didn't. On top of that, my code reader, which had told me which sensor was bad now has a communication error.
Anyway, car back up, sensor out, I used a little bore cam to look in the hole. I have no idea what I'm seeing, but if I rotate the wheel, (what I assume is) the surface of the hub looks terrible. I was worried I'd damaged it, but it's bad in so many places that It can't have been my grinding in one spot.
Here's a short movie (it may be upside down). I guess a hub replacement is called for, right?