Ratio Test
Cable & Casing
Ratio Adaptors
Drive Gears & Driven Gears

METHOD 1

1. Find a measured mile. Either a "Speedometer Test Zone" or use mile markers on an interstate highway. There are markers each mile in interstates, they are not always easy to identify, but if you pay attention, you can locate them.
2. Check the odometer reading, in miles and tenths of a mile, as you pass a mile marker and then check it again as you pass the next mile marker.
3. Check it again two more times to be sure that your reading is accurate.

1. Unscrew cable end at speedometer head
   
2. Attach a flag or a pointer to the end of the flexible cable. Use a paper clip or fold a piece of tape to form a flag.
   
3. Measure a distance of 52 feet 9-1/2 inches and mark the ends.
   
4. Roll the car up to the first mark so that the cable begins to turn. (You should have someone help you so you can keep track of the cable turns.)
   
5. Put a piece of tape on the car to align with the first mark.
   
6. Push or drive from the first mark to the second mark.
   
7. Count and record the number of full turns and tenths that the cable makes Ten full turns is correct for domestic cars. Note how many tenths of a turn either over or under ten full turns.
   
8. Repeat the test two more times and tell us the results. We'll build the right ratio adaptor to correct your speedometer reading.
   

METHOD 3

Write down transmission type, number of teeth on the drive gear, number of teeth on the driven gear, the rear end ratio, and rear tire size. Send it to us with a daytime phone number and we'll call you with the costs to build a ratio adapter from that information.

To Order a Replacement Cable: It's really easy to get the right replacement cable, or to order a new cable for a project car.

1. Measure the length of the old cable, or calculate how long the new cable must be. Allow several extra inches in length to accomodate possible error.
2. Identify the type of speedometer head (year and make of stock speedometer, brand of aftermarket unit)
3. Identify Transmission (year and make, screw-on end or plug-in end)

To Order a Ratio Adaptor: It's important to make accurate measurements in order to make the proper ratio change.

1. Decide where you want to install the ratio adaptor. They are usually installed to the transmission but they can be attached to the speedometer head, or the cable can be cut and tha adaptor installed in-line.
2. Identify the type of speedometer head or transmission where you want to install the ratio adaptor.
   
3. Determine odometer error using either of the three methods listed above.

Ratio Test
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To Order a Drive or Driven Gears: Speedometer ratios can often be corrected by replacing the driven gear.

Drive and Driven Gears are the gears at the transmission that drive your speedometer cable. The driven gear is easy...just undo the cable at the transmission and the gear is on the end. To get to the drive gear you usually must take the transmission apart. In that case it's easier and cheaper to get a ratio adaptor.

1. Determine the error in your speedometer. Use either method shown above.
   
2. Count the teeth on your driven gear Call us and tell us your speedometer error, the year, make and model of your car, and how many teeth on the driven gear. We'll let you know if the error can be corrected with a different gear or if you'll need a ratio adaptor.

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CALL US

2179 Macbeth Place, Riverside, California 92507

Ship To: PO BOX 51957, Riverside, CA 92507

After you've decided what you need and made your tests, give us a call and we can make your speedometer right again.

Phone (951) 742-7117   Fax (951) 742-7113
e-mail: info@speedometershop.com

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