Speedometer Driven Gears

[DalecarliaEric]

Hello everyone,

How many teeth does the Speedometer driven gear have as original in a 1965 Thunderbird with a Cruise-O-Matic Transmission?

My idea is to change the gear to one with a different number of teeth to increase the number of turns on the speedometer cable. When my speedometer shows 60 miles/hour, that equals about 96 km/hour, but I want the speedometer's 60 to be 60 km/hour. I see that there are gears with 16-21 teeth.

In short, does anyone know how many teeth there should be to get the speedometer to read km/hour?

Thanks in advance

[Alan H. Tast]

Hello everyone,

How many teeth does the Speedometer driven gear have as original in a 1965 Thunderbird with a Cruise-O-Matic Transmission?

My idea is to change the gear to one with a different number of teeth to increase the number of turns on the speedometer cable. When my speedometer shows 60 miles/hour, that equals about 96 km/hour, but I want the speedometer's 60 to be 60 km/hour. I see that there are gears with 16-21 teeth.

In short, does anyone know how many teeth there should be to get the speedometer to read km/hour?

Thanks in advance

First thing you need to know is what is the rear axle's gear ratio? There is a code on the data plate for that. There were a few choices from 3.00:1 and higher. Once you know how it's geared, then you should be able to do some additional calculations for the speedometer gearing.

There is no short/quick answer to this question - there are several steps involved to narrow down what you'll need. Complicating this is the desire to keep an English-unit display but have it register in Metric. The speedometer number plate was available in a Metric version with the speed range showing from 0-200 vs 0-120 for the English version used in the US/Canada. If someone out there is adventurous enough with scanning technology and 3D printing, a replacement insert set up for Metric would be interesting to offer.

[DalecarliaEric]

Hi,
Thanks for your reply. I'll check the rear axle gear ratio later. Good idea to print out a km scale.