My 1976 series 2 XJ speedometer suddenly went to zero and never bounced or had any problems before today. I understand these older series 2 cars might be different from series 3 cars with this transducer and so on (I was told they were purely mechanical cables). Any fix ideas?
S2 uses a mechanical speedo and may have a right angle drive gearbox at the transmission end. Your problem could be a failure of either of those, or the speedo itself. Most likely the cable, hopefully. If so, you may be able to find an instrument repair shop that can make a new inner cable, they just fit the ends in a tool to flatten the ends into a square drive. Maybe a pushbike repair shop can do it. Otherwise, complete cables are available.
total out is surprising. Indeed, the Speedo is mechanical. First and clean hands check is to remove the speedo and check whether the square end of the cable rotates when the car drives. If it does, second clean hands check is to install (temporarily) a known good speedo.
With a total out chances are that either of the two connectors have come loose or the speedo itself is shot. Even this isn’t that terrible, as used parts are around and pros repair your original speedo.
75 XJ6L 4.2 auto (UK spec)
Pop the speedo out and check back of the unit where cable goes in, then disconnect the cable, leave everything open and just drive the car a short distance, if cable doesn’t rotate then its the cable. New cables are pretty low cost, I carry a spare (mine is sometimes jumpy so I’m expecting a failure). If you have spare cable then you can connect to speedo with a variable speed electric screwdriver on the other end on VERY SLOW speed! That will test speedo. Personally I wouldn’t bother trying to repair old cable.
If you do test a speedo with a drill, it must be run in REVERSE!!
Typically 1500rpm gives 60mph