erroneous speedometer, 66 coupe

[Lincoln S.]

I have a 66 coupe, stock wheels and tires, and have noticed that the speedometer reads low.
For instance, when I am driving 55 mph the speedometer only shows 50 mph. Would I correct this with a larger or smaller speedometer drive gear?
Thanks, Lincoln Singer, 50240

[Michael G.]

Re: erroneous speedometer, 66 coupe

I have a 66 coupe, stock wheels and tires, and have noticed that the speedometer reads low.
For instance, when I am driving 55 mph the speedometer only shows 50 mph. Would I correct this with a larger or smaller speedometer drive gear?
Thanks, Lincoln Singer, 50240

Lincoln.....what is your rear axle ratio? The speedo gear for your tranny will color colded for the ratio. The gear, I believe, will fewer teeth.

[Lincoln S.]

Re: erroneous speedometer, 66 coupe

Michael, thanks for the reply. My 66 has a 3:36 rear axle. Thanks, Lincoln

[Duke W.]

Re: erroneous speedometer, 66 coupe

You also need to provide transmission type and tire size/revs per mile. Also, get error readings at different speeds to determine if it's an offset error, gain error, or some combination of the two.Duke