I have a 1989 740 GL wagon 5 speed 2.3 single overhead cam with 170,000 kilometers on it.

My speedometer has become intermittent in operation. Sometimes it will be fine and operate without any problem. Other times it may not operate from a stand still and suddenly work to fail again shortly after. It is worse when the car is cold than hot inside.

I feel the problem is in a poor connection to the speedometer as when it quits along with the odometers I can thump the top of the dash and it will usually start working again to quit if I go over a expansion joint or a pot hole. Thumping the dash will generally make it work so I tend to think it is not at the sending unit on the differential.

I've had the instrument cluster out about four times to see if the connection is poor. The plug I assume to be the speedometer connection is the white one with four wires that plugs into the base of the back of the speedo (VDO type). The connection appears to be good but the problem still persists. I have cleaned the contact strips on the printed circuit, but without any real improvement.

Everything else on the instrument cluster works fine.

Would anyone have any ideas as to what I should examine to see if there is something I can do to fix this issue ?

Thank you,
Steve B
Calgary AB Canada