[peteb]

Hi,

My '86 has this problem. After not being driving for a while the speedometer may stick at zero. A tap on the speedometer "fixes" the problem. I may go months without seeing the trouble again.

You are correct that there is not a speed cable. Late cars have an electronic speedometer. Does your odometer still work? I could see mine turning while the speedometer was stuck a zero. This is proof there is a speed signal getting to the speedometer electronics.

I'm fairly sure the trouble is in the connections to the moving armature coil/spring assembly. I have no 100% proof. I couldn't find a specific problem when I had my speedometer out of the dash. Not a mechanical sticking issue for me. Everything moves freely. No obvious trouble with the circuit board/driver electronics. I'm just kind of guessing based on my experience with analog meters and not finding other problems.

There are four electrical connections between the moving and stationary parts of the speedometer with clock springs in between. They are all delicate so I didn't attempt any rework for the risk of breaking the speedometer. What may happen is the the connections pick up some corrosion after sitting and go bad. Any movement such as a tap, makes a connection. After that the movement of the speedometer keeps the connection good until the car is parked for awhile again.

I'm ignoring the problem for now. I did pick up a spare instrument cluster as a backup in case of a complete failure.

All part of the fun with old cars..

Peter