Hi, since the speedo and odo in my recently arrived 308 (GTS '78) didn't work I checked and fixed several things. Still no luck. So I finally found the sensor not working (too, the speedo itself was broken as well). I dismounted and opened it as described at dinoplex and found it was standing in oil. After cleaning it already seems to work using my scope. It looked quite worn and surely leaky from the upper side. But since it was nearly full of oil I wonder if the oil maybe also penetrates from the gearbox side? The gearbox mounting looks (reasonably) dry though. Thanks Marc
Same thing happened to me on my 87’ 328. My sensor was faulty and when I removed it, a whole lot of oil came out. Most probably caused by a faulty shift shaft seal where engine oil is leaking into the transmission. Replaced the seas and alls well now. The sensor was faulty though and required replacing.
If the breathers are not working it will pressurize internally and push oil places it does not belong.
I've had several friends experience speedometer sensor failure (including me). If you've disassembled the sensor, cleaned up the internals and (somehow) confirmed they are still working, you might consider reinstalling them but "potting" the assembly rather than just using factory o-ring style seals. Potting the electronics will stop oil from contacting them. Here is an example of potting epoxy: Amazon: MG Potting Epoxy I have replaced my sensor with a potted sensor, but used a prototype replacement board. Here is a link to the war story: Need failed Speed sensors
I have cleaned it up, renewed the wiring and reassembled it. I have not filled it with resin but sealed it with a new o-ring and silicon compound. Finally I put a heat shrink tube on top and bend the hose downwards, thus it should be 100% protected from the upper side. I did not touch the sealings from to lower side since these seemed fine on closer inspection. The oil is coming coming from the rear cylinder head and covers all the engine downwards which I have to check and fix. The speedo works fine for now.
