I am attempting to replace the rpm sensor on my 89 740. Can I access it from inside the engine compartment or do I need to climb underneath the car? If anyone can point me to a picture of where it is located, that would help immensely.
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1989 740GL 177k

I think your 740 is similar to my 940. I replaced this sensor using a short box wrench (10 mm I think) which I could put on the mounting bolt by feel down on the top of the bell housing. I could barely see the sensor and bolt by sighting down along the firewall but not when I had my hand down there with the wrench. It was an easy job though. PBlast first for a day or two would be wise although the sensor on my car came out easy once the bolt was out. The bolt came out easy also.

It is located directly behind the engine on the top of the bell housing. It is a little easier to get to on a 700 series car than it is on a 240,

Bolt is 10mm. Be careful removing the sensor they sometimes are stuck and you do not want to break it off. Doing so will mean removing the transmission to get the broken end out. Good place to use PB Blaster prior to trying to remove it.

Randy