Hi friends. I’ve been piling on the miles in my 1949 Olds 88 this summer… a little TOO many! Here’s the situation:
my speedometer consistently reads 7mph faster than actual. That means the miles are racking up quicker than I’d like. It’s a very low mileage car and I don’t want to add more than actual. I’ve cleaned the gauge by dusting it with compressed air carefully, I’ve lubricated and examined the actual cable, I even removed it from the sheath. I’m running close as possible to stock size tires (225/75/R15). What I think I need is a speedometer recalibration. Can anyone recommend a shop to perform this service?

found Mr Peanut on the last adventure!! Posted the pic for fun.

 

There used to be speedometer shops all over the place .
But since most speedometers are electronic now , they have mostly disappeared .
Perhaps try the " services offered " section of Hemmings Motor News for a speedometer shop .

 

¡Lo me gusta! 😎 Every time I see this 49 I like it more!

Bob's Speedometer Repair in Howell MI comes highly recommended in AACA. www.bobsspeedometer.com

 

I'm not familiar w/ vintage '48 transmissions, but if it has a speedo gear like used on later cars, why not just change the speedo gear (assuming they are even available for your trans)? I would think that the only way to "calibrate" a speedo is to first check to see of the speedo and odo are in sync (i.e. exactly one mile is logged on the odo when the speedo is at an indicated 60 MPH for 60 seconds). About the only thing that can degrade this ratio as the speedo ages is that the magnets and indicator spring get weak over time. Weaker magnets would cause the speedo to read slower than actual, weaker springs would make it read faster than actual. There may be a zero-offset adjustment as well (an issue I have on my speedo). But if that ratio is intact, the only way to correct it is w/ a speedo gear in the trans (or an external speedo gear box like is used for cars w/ high numerical ratio rear ends).

 

Thanks! I’ll explore further and keep all posted on what I do. I’ve heard from others this 7mph difference is very common.

 

Is the error a fixed number, ie, 7 mph off at say 25 and 60 mph? Or does the error get worse with speed? Either of these indicate that the speedo head needs to be recalibrated. If the car is stock (I'm assuming so) the gearing should be OK.