Speedometer Ratio Adapters: US$85 postpaid in North America.

These are Stewart-Warner type 800 metal gearboxes. They can be mounted on the transfer case or transmission or on the back of the speedometer. They are about 2 inches long and a couple of inches deep.

They can be made in a wide range of ratios to correct for changes in tire size, or changes in differential gearing or both.

In many applications, it is very easy to mount on the back of the speedometer. Mounting on transfer case or transmission (wherever the cable goes in) is often tricky because it can be hard to get to. Usually, if you can cup your hand behind the speedometer and unscrew the cable, you will have enough room there to put the adapter.

They use two 5/8 inch fittings when going between the cable and the speedometer, and two 7/8 inch fittings when mounted on the transfer case or transmission. These two fitting sizes are almost universal, good thing because they are the only two sizes available.

What do I need from you?

1. mounting location, speedo or transfer/transmission case.

2. ratio change...tell me what it reads now and what you want it to read...here are some ways to do this. (contact me if unsure about this)

• you can determine this ratio by telling me the diameter of the old tires and the new tires (measure the same way, if one tire is on the car, measure its diameter horizontally because the weight of the car compresses the tire in the vertical direction)
• if you changed the differential gearing, what was it before and what is it now
• using a measured mile, check what the odometer reads for a measured mile (or over more miles for a better reading) compared to what it should have read.
• a less accurate way is to use another car to tell you what the correct speed is while you note the speed on your speedometer. With these two numbers, the ratio correction can be determined.

3. Please confirm that the fittings sizes are correct and that you have square drive cable...but really, this will be ok for nearly all vehicles made in North America before the 80s, but I don't know about foreign applications...if metric the adapters won't fit. You can check this by unscrewing the speedometer cable and measuring the ID on the cable fitting.

Note that these work only on the older type of mechanical speedometers made up until the 80s or so....they DO NOT work on the modern electric ones. If you have little lights that give the odometer reading, these adapters won't help you.

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