Electric speedo question for fox body donor builds (gear size)

[jakester888]

Using all donor parts from a 93 Mustang.

I have autometer electric speedo gauge with electric sending unit from Forte's. But the gear on the Forte sender doesn't seem right because The speedo shows 10MPH when I know I'm at least 20. So I'm thinking it must be the wrong gear size.

What gear size did you donor builders use for speedo-sensor to autometer gauges? Choices range from 16-tooth to 23-tooth on Breeze's website.

[michael everson]

If its electric, then it is programmable. No need to change anything. Look on Autometers web site for more info.
Mike

[donshapansky]

MY 33 HR is having a different issue with the electric speedo, it shows zero even though it's going maybe 10 mph then does huge flop to 40 - 50 mph and back to zero again like seized speedo cable but there is no cable! Any ideas? The gear supplied says it's for 3.73 rear axle and I have a 3:55 and I know there needs to be a calibration done, but something else appears to be wrong.
Don

[DaleG]

Here ya go: from Autometer's site http://www.autometer.com/media/manual/2650-1512-00.pdf

Calibration (Electric Speedometer calibration made easy!)To calibrate your electric speedometer:

1. With the power off, push and hold the Trip/Reset button. While holding the button, start the vehicle and continue to hold the button until the pointer sweeps to full scale and stays at full scale. You may now release the button.
2. Drive to the beginning of a pre-marked 2 mile (2 kilometer) distance and stop. It does not matter how far away it is to get to this pre-marked 2 mile (2 kilometer) mile distance. Do NOT shut the engine off . Push and release the Trip/Reset button. The pointer will drop to half scale.
3. Drive the 2 mile (2 kilometer) distance. The pointer will remain at the half scale position no matter what speed you drive. It will be normal to see the LCD odometer counting rapidly as it is receiving a speed signal. If you have to stop during the calibration, that is o.k. The speedometer will simply stop counting pulses durng this time.
4. At the end of the 2 mile (2 kilometer) distance, stop and press and release the Trip/Reset button. The pointer will drop to 0 and the calibration is stored. You are now finished.

Remember the accuracy of your 2 mile (2 kilometer) distance will directly affect the accuracy of your speedometer.
The following list contains factors that can affect speedometer accuracy and how to minimize them during calibration.
1. Tire diameter increases slightly as vehicle speed increases. To minimize this error drive at an average speed of 45 MPH (75 KPH) during calibration.
2. Tire diameter increases slightly as tire air pressure is increases. To minimize this error, check the vehicle’s tires to ensure correct air pressure.
3. Tire diameter changes with vehicle load. Minimize this error by having an average load in the vehicle during calibration.
4. Minimize tire slippage error by not breaking traction during calibration.
Note: Always recalibrate speedometer after any tire size or differential ratio change.

[jakester888]

Awesome, thanks.