THE SPEEDOMETER SHOP WWW.GAUGEGUYS.COM
Address: 9632 Humboldt Ave S,
Bloomington, MN, 55431-2629
U.S.A Lower 48 only please.
WHY YOU SHOULD NOT DEPEND ON GPS FOR A RATIO TEST:
In most cases, people needing ratio adapters are working on older vehicles. Unless the speedometer head has been serviced and calibrated by a qualified tech, there is a good chance that the speedometer head is out of calibration.
GPS will tell you how fast you are going compared to what your speedometer is indicating, but will not tell you if your odometer or cable delivery is correct. So this is why we recommend doing 1 of the 2 test's shown below. It may take a little longer but we will get it right the first time ;).
In most American vehicles, The speedometer calibration is based on cable delivery of 1,000 cable revolutions per mile driven. Changing tire size,wheel size, transmissions and rear end ratio's can often alter the cable delivery and cause your speedometer to read incorrectly. If this is the case the ratio has to be established The following tests are designed to tell you if the error you are experiencing is in the speedometer head itself or in the cable delivery from the transmission that is where an adapter will correct your problem. THIS IS EASY TO ESTABLISH Just conduct 1 of these 2 tests and it's done.
THE EASY WAY TO TEST RATIO:
1. Stop on a mile marker (found on most US highways), Record the odometer reading including the 10th.
2. Drive 10 miles and stop, record the odometer reading again, including the 10ths.
3. Subtract the 1st reading from the last reading, this will tell me if the cable delivery (Ratio) is correct or incorrect, if correct the subtraction number should be 10.
THE HARD WAY TO TEST RATIO:
1. Check if the tire pressure is the same as advised by the factory.
2. Measure (by making chalk marks) a distance of 52' 9"1/2"-16.09 mm.
3. Unscrew speedometer cable at the speedometer head.
4. Mark the inner core with a paper flag, paper clip, or preferably a hairpin.
5. Push or drive vehicle over the entire distance, counting the full and partial revolutions of the cable.
6. Always roll car towards the first marking until you see the inner core start turning to eliminate the gear clearance. Before you start counting, mark the part of the vehicle that is exactly over the beginning of the line. Stop counting when the marked portion of t5he vehicle is exactly over the end of the line.
7. Repeat this procedure 3 times and jot down the results:
If odometer reads correctly per 10 miles driven after the EASY TEST, there is no error. If the cable turns 10 times after conducting the HARD TEST, there is no error.
If reading is incorrect, a ratio adapter will solve your problem!
Although rare, you could have both cable delivery and speedo head problems. In any event your cable delivery must be correct in order for the speedometer to be accurate.
For foreign car's conduct the same test and then call the Tech. Line @ 952-881-7095 and a Tech. will advise you of the necessary additional step's that may need to be taken.
Metric Offset Or Straight Through Ratio Adapter
Thread: 22 x .5 mm
Ratio .3600 - 2.7770
Ford Ratio Adapter
Right Angel Speedo/ Tach Adapter
Standard Offset Or Straight Through Ratio Adapter
Thread: 7/8 18 thread
Ratio .3600 - 2.7770
All Ratio Adapters Must Be Ordered Over The Phone
Call: 952-881-7095 Between 8:30am-6pm CST
If an order must be placed by email, expect a 3-4 day delay