Hi I have a xj40 1990 and for some reason the speedo keeps on breaking down, i could be driving down the road and then all of a sudden it goes off with just the rev counter worker. It sometimes comes back on ten minutes later or to get it back on straight away i have to bang it hard on top of the dash board, but sometimes it does not come back on.

Can anyone please let me know what the problem is, as the garage could not work it out

many thanks

 

in2town, is the odometer still ticking away? If the odometer is still counting up the mileage, then the problem is almost garanteed to be inside the instrument cluster (read as get a new instrument cluster). If the odometer does also stop working when the speedometer stops working, then I would be looking for a common problem. I don't know your car extremely well, but a check that I would do first is look at both ends of the speedometer cable and see if the square ends have rounded. You can also try spinning one end and seeing of the other end spins too. It is possible the square ends have rounded and are slipping periodically or the cable has snapped/worn through and the frays periodically are enough to allow the cable to spin on both ends.

HOpefully this gets you going in the right direction. The tranny end of the cable should be pretty easy to pull off. The hard part is just getting under the car. From there, it should be a single cap that you pull off and it will allow the cable to slide out. I have heard of people using a drill on a semi low speed to see if the speedo moves. Just make sure to start off slow so you don't over speed the speedo.