[T3] Recalibrate speedometer

[Jim Adney]

On 9 May 2015 at 4:51, Mike Fritz wrote:

> Or, you could remove the speedometer and cable. With the cable attached 
> to the speedometer, use a drill to get the speedometer going at a 
> certain speed, say 20 MPH. Tape the trigger on that drill so it stays at 
> that speed. Then, remove the needle and reposition.

For problems like this, I use a short length of the flexible inner 
speedo wire chucked in a drill press, run in reverse. That runs at a 
fixed speed and I first run it in a good speedo to see what the speed 
reads out as. Then I transfer to the speedo that needs to be reset 
and see how far off the needle is. Then adjust the needle position.

This usually requires a few trials until I get it right.

It's quite unusual for this adjustment to be necessary, because it's 
almost never necessary to disturb the needle position on the shaft.

I've only had to do this once. That was on a speedo that someone had 
repaired by installing a new needle. They did a very nice job, but 
they didn't notice that the needle hub has a counterweight, to offset 
the unbalanced weight of the needle. By random chance, the new needle 
was attached in line with the counterweight, so that the 2 weights 
added instead of canceling out. The result was readings that read low 
until the needle pointed straight up, and high thereafter.

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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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