Report about my way to replace broken K75 K100 speed sensor. I broke it by removing it from the final drive. So don't remove the speed sensor, just unplug it!

I got upset after I realised the sensor was broken only because of my unnecessary actions. I got more upset after seeing the price 80-150€ for new sensor + the wait for it to arrive. The 30€ used one didn't sound too good either. So I decided to find a replacement from some local auto parts store.

There could be many more and better alternatives but this was the one I found feasible and was available.

The replacement sensor is Opel crank shaft sensor. Intermoto 18987. Like this:
CRANKSHAFT POSITION SENSOR 18987 for OPEL ASTRA FIAT 10456604 1238938 71739726 | eBay





I got it for 25€. It is much more inexpensive than the original and brand new. The original sensor is 14,5mm in diameter while this one is 13,5. It leaves space for some thin o-rings to seal the hole. The original sensor should be 3k ohms (correct me if I am wrong) and the replacement part is 2,38k ohms.

I measured the signal from the sensor with oscilloscope and it should be fine. I don't have a working original sensor so can't compare but I did compare with K-diag speed signal. It works up to 100km/h. 100+ kmh i have no data. In theory the signal voltage could climb too high with enough speed. The sensor has smaller diameter and smaller resistance -> I assume the coil is smaller so it should't happen. 



I added some electrical tape and o-rings so it would sit nicely on the hole. The screw hole was to far away from the sensor so I enlarged it a bit. I also soldered the original wires to the sensor.



Thoughts? Should this be added to the tech page? It isn't a straight fit but seems to work nicely.

I removed the sensor on my Brick once to inspect it for cleaning. It didn't need to be cleaned.   I change the rear drive oil every season. What broke on your bike's sensor?

My K75 haven't been on the road for 10 years and I bought it last September. I changed the final drive oil and put some moly grease on the shaft. The original speed sensor worked just fine before my maintenance on the final drive. The sensor should have some 3k ohms but it had none. There was no continuity between the wires. My best guess is that the coil is damaged from the removal of the sensor. The sensor was quite stuck so I think it got a bit too harsh treatment. I checked the wiring all the way deep into the original sensor. It wasn't the problem.

The car sensor reads the gear on the final drive just fine and everything is working. I even reused the original wiring. I just might have to use some more tape or something to smooth out the esthetics of the new sensor and wires

Nice job. BMW seem to have fitted two types of speed sensor:

- the early type which you can take apart and usually breaks on being removed from the rear wheel if there's any corrosion holding it in the hole
- the later resin-sealed type which is bombproof.

The early type is distinguishable by having two screws in it instead of just the one holding it to the bevel drive. The second screw releases the cover and lets you get at the (usually) corroded wires inside. I repaired one once by soldering in two completely new wires, but it died about six months later when corrision ate through the small brass pin that held the wires.

Dai wrote:- the later resin-sealed type which is bombproof.

It seems that I have managed to break the later model sensor. And I know it is sealed unit but I got through it all the way to where the wires meet the pins for the coil. All intact. It doesn't seem to be a fragile part because it feels quite sturdy. Considering the miniature coil it has sealed somewhere in the tip, temperature differences, age and vibrations is has gone trough - maybe it is understandable that it might brake when forced out of its resting place.

Finding the replacement was quite a tricky task since most inductive sensor for cars are larger units that wont fit the hole in the final drive. And no one ever specs the size! There is also a ton of hall-sensors used as position sensors (crank or cam sensor). The sensor I found is far from perfect but it seems quite common part (at least in Europe). One can get it from store without waiting or paying for the original.

The way I do it is to spray with penetrating oil to try and lubricate the corrosion, then grip the base of the sensor as close as possible to the bevel drive with a small pipe wrench (not vise grips/mole wrench or pliers). I then work it gently from side-to-side, adding more penetrating oil as it starts to move. I've successfully removed two stuck sensors this way.