Go the parts store and ask to see one of the gears. On the back of the package there generally is a chart which tells you how many teeth to change. You will need to time how long it takes your car to travel 1 mile traveling 55 mph on the speedometer. The chart will then use this time to determine the number of teeth to add or subtract from your current gear, the driven one which your cable goes into. If for some reason you come up with a number that is off the chart then you will need to change the driveing gear which is mounted on the transmition output shaft. From the numbers you are saying I'll bet you will have to change the gear on the transmition shaft. Also the chart I'm talking about is published in the Ricks First Generation catalog. If you don't have any of these just time how long it takes your car to travel 1 mile at 55 mph and post the numbers and I can get the info for you. Also post how many teeth your current gear has.
I should add you will need to time between two mile markers so you know when you have gone one mile. It also helps to do it between two miles of markers and then divide the time by 2 to be more accurate.
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