* Transmission Type: The speedometer gear is matched to your specific transmission. Tell me what type of automatic transmission you have (e.g., TH350, TH400, Powerglide, etc.)
* Rear Axle Ratio: The rear axle ratio determines how many times the driveshaft turns for each rotation of the wheels. The speedometer gear must be compatible with this ratio.
* Tire Size: Your tire size impacts how far the car travels with each wheel rotation. This also affects the speedometer gear selection.
How to Find the Information You Need:
1. Transmission Identification: Look for a tag on the transmission case. It should have a model number (e.g., TH350).
2. Rear Axle Ratio: Check the Vehicle Identification Number (VIN) tag on the car's driver's side door jamb or the glove box. The VIN can help you decode the rear axle ratio. You can also look for a tag on the differential housing.
3. Tire Size: Look at the tire sidewall to find the size.
Once you have this information, you can:
* Use a speedometer gear calculator: Many online calculators can help you determine the correct speedometer gear based on your transmission, rear axle ratio, and tire size.
* Consult a parts catalog: A Chevrolet parts catalog will have a listing for your model year Impala and you can find the correct gear based on your specific transmission and axle ratio.
Important Note: Using the incorrect speedometer gear will lead to inaccurate speedometer readings.
