How to recalibrate a speedometer if you took off the needle!

[jonr]

Speedometer calibration in a nutshell:
(For those of you who pulled the needle off by accident - this does not work for matching tires to your speedometer)

What you need:
-variable speed drill with locking trigger
-stop watch

1. With bezel removed, mount speedometer assembly inside of orange housing. Put the needle back on spindle so it returns to zero in a natural fashion.

2. Attach the speedometer cable to the back of the speedo and the other end to the drill.

3. Get your stop watch ready and start your drill up until you get what appears to be 20 MPH. Make sure speedo cable does not slide out of the jacket (you may have to rig something up or hold it in place).

4. As the odometer starts to slowly rotate, make a visual note of where the number of your choice rotates past a reference point. All the numbers on the speedo are the same height so when the top of one number passes the top of another, it can be reference.


5. Once you have decided on a reference point, start your stop watch and clock how long it takes for the 1/10th mile number to make a complete rotation on the odometer. Try to be as exact as possible. This is critical.

6. Convert your stop watch time into seconds. Divide that number by 60 to get minutes. Divide it again by 60 to get hours. Then take 1 mile and divide it by how many hours you?ve accumulated on your stop watch.

For example: one of my trial times was 4 minutes 21 seconds. That?s 241 seconds. 241 divided by 60 is 4.35 minutes. 4.35 divided by 60 is .0725 hours. 1 mile divided by .0725 hours is 13.79 MPH.

7. So now you have an idea of what your speedo should have been reading. So, hold the spindle in place back by the magnet at 20 MPH and then force the needle down or up to your calculated speed (in my case, about 14 MPH). Technically, this should be it, but let?s repeat to be doubly sure.

8. Repeat another trial and this time increase the speed of the drill so your speedo reads at 50 MPH. See if your calculation is once again accurate and adjust the needle if necessary. If you do not have to adjust the needle, then you?re done! If you did, then do another trial to check your results.

That's it!

-jon

[back_online]

Ok, I'm gonna climb way out on the 'stupid' limb here and ask:
Why can't ya just put it on Zero (or approx where zero should be)
and ride next to a buddy's car when he's doing exactly 30mph? If it's off by 5 mph, stop, move it down a little and retry?

[jonr]

Back_online,

You could surely do it that way, but I'm not sure how accurate it would be. The friend's vehicle would need to have perfect speedometer calibration to provide as an accurate reference. Also, you would have to be able to hold a constant speed. You would also need to disassemble the speedometer housing every time you want to calibrate the needle since you have to hold the back of the speedometer axis in place to move the needle.

I think what you have pointed out could indeed work, but if you already have the speedometer out and disassembled, it takes a lot less time and effort to calibrate this way (assuming you have a variable speed drill with a trigger lock).

-j