Wondering what is the sensor is on the differential cove above the fill screw?
Speed Sensor? Differential oil sensor?

 

Speed Sensor.

 

thats the pickup for the speedometer. there's a 'tone ring' around the output shaft, and that sensor detects it, the speedo shows that as MPH.

 

Thanks. Yeah, we just re-newed the old cover, the cover I ordered from Rock Auto didn't have the sensor hole, or sensor for that matter on it.

 

You should get one from a 740/940 at a scrap yard. They're aluminum and thus will not rust or bend.

 

Great call. I ordered one from Rock Auto (it didn't have a hole for the sensor). Crazy thing, I told them it was wrong the wrong part, they gave me the part, credited me the price for the part but didn't credit me the shipping. So, we renewed, soldered the old one. It's good for now. I may go pull one off one of those rides in the yard near me so I have it ready.

Do the 740/940's have the sensor there too?

 

Yes, all rwd Volvo have electronic speedos from I believe 85. The 7's had them from 82. The cover bolt pattern is identical; they do use a different sensor but they use the same sensor. If or some reason the speedo does not work correctly after the swap, switch the two wires in the harness connector.