Bench Testing a Speedometer

[dirtrack49]

Can anyone tell me the correct procedure for bench testing a speedometer?

In another thread, it was stated that you could use a variable speed drill with a small screwdriver bit to turn the speedo. I am not sure how that works.

Is the screwdriver bit making contact with something, or does the revolving bit cause a magnet within the speedo to turn?

I had taken the speedo out to lube the cable and add some white grease to the input housing. It makes noise off and on. So before reinstalling it in the dash, I wanted to operate it out of the car to see if the noise is gone.

I am aware that many people have sent their speedometers and tachometers out for repair when they start squealing and most likely I will end up doing the same. However, I thought lubing it first may make a difference.

Thanks in advance for any and all suggestions.

 

[dirtrack49]

Boy do I feel stupid. I just went out and took another look at the speedo input housing after removing the grease and realized that there is an inner shaft that can be turned with a flat screwdriver end. It is just like every other speedo drive that I have seen in the past.

Guess it is time for a more powerful set of glasses.

Now my question is, can you do any good by lubricating this input fitting? Most likely the noise is coming from the cable, or internally in the speedo. Any thoughts?

[mmizesko]

Tom,

I know I sound like a broken record, but unless you like frequent bloody knuckles from taking your dash apart multiple times, I'd get it all done at one time.  The cables for the speedo and Tach are cheap, and not too difficult to replace (don't forget string trick).  Lubricating the outside shaft is useless if you have a howling tach or speedo. Texas, my friend.

My philosophy would be while you've got it all apart, replace or repair anything back there, as well as the bulbs.  And you may want to check out the LED threads, as I am thrilled at the brightness of my instruments now.

Good luck with this.

Mike Mizesko
Columbus, OH

[dirtrack49]

Thanks Mike for your input. No, you don't sound like a broken record. My problem is, I come from the old school method that there must be a fix somewhere that I can perform before sending it out to the experts. I either completely screw it up dicking around with it and end up sending it out, or I get lucky and solve the problem.

So...this is what I have found so far:

The inner shaft where the speedo cable inserts into the speedo, has some play to it. This I would think is normal. However, when you run the speedo with a drill (in reverse by the way), I find that the speedo can be either erratic or squealing depending on where the inner shaft is located or riding on the outer shaft housing. This leads me to believe that either the inner shaft needs lubrication, or there is excessive wear between the inner and outer housing of the speedometer drive.

Somewhere, I remember someone talking about the need of making sure that the speedo cable did not cause the drive mechanism to bind causing a squeal in the instrument itself. It appears from bench testing the speedo, that when the inner shaft is pulled out to it's maximum limit within the housing, the speedo begins to squeal.

Any thoughts?