1992/740 Non Turbo with 220K miles ...
I've been having trouble with the speedometer (erratic behavior, flicking of speedo needle, needle often at zero, etc. much reported on cars of this age/vintage). Also doing some tune up while the car is off the road -- so I decided to jack up the back of the car, remove the differential housing cover, take a very good look at the speedo sensor and drain/renew the rear axle oil while I was about it. Got a bit more than I bargained for:

1) I got the differential housing cover off after a struggle (I might have jacked the car up higher to make it easier). When putting it back on, should I use a gasket sealant? [The previous seal (factory?) did not appear use a gasket at all, but a thin layer of red sealant that took a while to scrape off. I have a gasket from IPD that looks like cardboard -- like I could have made one myself out of a cornflakes packet.]

The speedometer sensor looks OK -- but the wiring to it contains no boot at all -- the 2 wires look intact and connected though the green one is bare for the last half inch. The wires go into a grey plug which plugs into the housing of the speedo sensor (which is black). I wanted to disassemble it all and clean it in comfort rather than contorted and freezing under a Volvo 740. Had to settle for the latter though because the grey plug refused to come out fully from the housing with reasonable force, so not wanting to break it I pushed it back into the sensor housing and removed the sensor itself from it's housing in the differential cover (after removing its allen screw, I prised it out without too much trouble).

2) The grey plug that proved so obstinate was secured to the speedo sensor housing with a thin wire strand which I duly cut and pulled out with some pliers. Do I need to replace this thin securing wire? If so, what is this called and how would I do it?

3) I am concerned that I have damaged the grey plug / and or sensor by trying to separate them (the latter which costs $160 and the former I can't find to buy on any website and isn't mentioned in any of my Volvo manuals). What I'd like to to is make sure the connections are seated properly again, then cover the bare wire with heat shrink and then another heat shrink as a boot over both wires. Any comments on this approach? [It seems to me I'm missing some simple way to open the grey plug which carries the 2 wires to the sensor].

4) Is there a way to test the sensor -- say with a multimeter? [After all this I have a nasty feeling my speedometer problem was the speedometer itself all along].

5) I'm thinking of using Mobil Synthetic Gear lubricant 75W-90 (API GL 5). Would this be OK?

6) Generally, does it make sense to replace the rear axle oil in a car of this age -- or has this all been a very educational waste of my time?

Thanks,


Rob2Volvos