Speedometer going slow

Joop

Joop

Well-known member
Took out my car yesterday and used my GPS

It shows 5 miles less than actual speed (if we can trust the GPS)

Speedometer is a still sealed unit from my unrestored Coupe.

Cap on tube reads 9 - 34 19

I installed an original cable some time ago.

What can I do to correct this situation.

Thanks

PS. could not find an old thread to match this problem
 
If in fact you have a 19 tooth gear as the cap reads, then install an 18 tooth gear. That will get you closer to the right speed. I'd find accurate mile post markers, or drive exactly one mile in your modern car, noting the exact start and finish locations, then drive the Model A the same distance and make sure the odometer is accurate first. After the odometer is accurate, then you can tweek the speed from inside the speedometer by adjusting the spring, which is probably best left to the guys who work on them all the time.
 
If you are running 19 inch Firestone tires that would account for the indicated error since those tires are approximately 6% to big in circumference. If you are using the new 19 inch Goodyears, they are almost exact in dimensions and the error would be in your speedometer.

Errors in indicated speeds can be corrected by an adjustment inside the speedometer. You will have to break the seal in order to make the adjustment.

Gar Williams
 
Before you do anything determine where the problem is located. You should check the odometer for accuracy. The odometer readings will tell you if the gearing and tire diameter are correct. If the odometer is reading correctly and the speedometer is off then you can adjust the speedometer independently from the odometer. There is an adjustment for the speedometer. See the following article for details.

http://www.modelahouse.com/tech/speedometer/fischer.html


Bob
 
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