Testing a speedometer with a drill

[7Dcuda]

I want to test a speedometer in a used non rallye gauge cluster I just bought.  Seller says speedo worked when it was pulled out of previous car but I want to test it by hooking up a new cable that I have and using a drill before I install it.  Do I put the drill on forward or reverse do this this?   

[NC RMP]

I had mine out and had to have it rebuilt and I did the same thing to test.

I don't think it matters as the reverse direction won't spin the needle (otherwise it would go backwards when you backed up) but you can also just put something in the slot and quickly twist it with your finders to see which direction makes the needle jump.  Then put the drill on it in that direction.

[purple1]

I can remember you need a reversable drill if you want to back up the miles on the od. 

Does that help 

[7Dcuda]

I can remember you need a reversable drill if you want to back up the miles on the od. 

Does that help 

No, dont want to back the miles up...just want to test the speedo to make sure it works before I install it.  Further research shows the drill should be in reverse to test it supposedly.

[purple1]

No, dont want to back the miles up...just want to test the speedo to make sure it works before I install it.  Further research shows the drill should be in reverse to test it supposedly.

All you can do is see if it moves or not. You can not tell if after installed it will be acurate or will jump all over the place and snap off the needle. And I was kidding about backing up miles. E-body speedo will not back up like that.

[NC RMP]

Yes, as you don't know the exact RPM of the drill all you will know is that the speedo needle rises, the miles click off and it does so quietly.  My speedo does 24 MPH at full speed of my cordless drill.   

I had to test mine because the original was making a really bad squeal sound from time to time.  I pulled it out and ran the drill on it for a while to try to make it do it out of the car, which I did finally.  It was the speedo and I had to get a rebuilt one.

[73EStroker]

And you run the drill in reverse to test it in its forward direction. Run the drill forward if you want to take the time to wind the odometer back but why? These cars are so old now no one looks at the mileage anymore except on multi $$$ original collectibles.