Re: non working speedometer

Posted by 39SixSedanMan On 2017/12/19 8:01:56

First, there are multiple contributors to the system's function, The driven gear at the transmission tail, the cable and the speedometer.

Second, of these three contributors, the typical cause is old dried oil and grease in the speedometer head itself. Once this happens, the torque to drive the head begins to rise. Eventually, this causes the cable to twist, kink (making noise) and eventually break. For those systems with plastic driven gear in the transmission, the gear itself will sometimes strip.

So, make sure you have a good, lubricated cable and driven gear. Also, if you are able and confident to do so, make sure the input shaft to the speedometer is oiled lightly. Most have a small brass plug that retains a felt wick oil reservoir. Do not use grease here, but a very light oil.

Next, the worm gears: clean off any dried grease and replace with a modern silicone type.

Finally, the odometer wheels: this is most difficult and often overlooked. Because of the very large gear ratio between the input shaft and the odometer wheels, any friction between the wheels, their internal gears and the center shaft is multiplied. This means it is very difficult to turn the speedo input shaft if the wheels are stuck. Lubricating them is usually a practice in patience, and sometimes requires disassembly, which the original manufactures (Stewart Warner, King Seeley, etc) didn't plan for.

I hope this helps. Although I am an old car owner first, I've put my engineering background to work for a side business to repair speedometer/tachometers.

Pat