FNQTan
I have a B21E Volvo 244 1979. When I acquired the car, it had been sitting for a couple years. After about 500km of driving the speedometer failed. So, I took the instrument cluster out and drove the car to see if the wire inside the speedometer cable was spinning while driving. Turned out it wasnt. This told me the issue wasn't in the instrument cluster. My model has a mechanical sensor - a cog that spins in the transmission. I opened the housing on the tranmission end and found the cause of failure - the old speedometer wire had rusted and split at the tip.
I bought a new speedometer cable, o ring and seal from IPDusa. I cloth taped the new speedometer cable to the old one and fed it through from inside the car. Took it for a test drive and the speedometer wire was spinning while driving. Hooked up the instrument cluster and I now have a speedometer back in action.
The o ring supplied by IPDusa was too large! So I just used the old o ring.