700R4 Speedometer Gear Calculator

What Are Speedometer Gears?

Speedometer gears are small plastic gears inside your transmission that drive the speedometer cable. The drive gear is pressed onto the output shaft, while the driven gear connects to the speedometer cable. When you change your rear axle ratio or tire size, the speedometer reading becomes inaccurate. Replacing the driven gear with the correct tooth count restores accuracy.

How to Use This Calculator

• Step 1: Enter your rear axle ratio (e.g., 3.73, 4.10, 3.08)
• Step 2: Select your drive gear teeth (700R4 common: 7, 8, 9, 10, 15, 17–25 teeth)
• Step 3: Enter your tire size (e.g., 275/60R15) or directly input the tire diameter
• Step 4: Click "Calculate" to see the recommended driven gear

700R4 Speedometer Gear Reference Chart

• Drive Gear Options: 7-10 teeth (early models) or 15-25 teeth (later models)
• Driven Gear Options: 34–45 teeth with color codes: Red (34), Purple (35), Yellow (36), Green (37), Gray (38), Blue (39), Orange (40), White (41), Pink (42), Black (43), Tan (44), Natural (45)
• If calculated gear is not available: Use the nearest available and add an inline speedometer correction adapter (±2% increments)

Why Accurate Speedometer Matters

An inaccurate speedometer can lead to speeding tickets, incorrect odometer readings (affecting resale value), and unsafe driving conditions. For 700R4 transmissions, correcting the speedometer gear is essential after any gear swap or tire size change.

Troubleshooting Common Issues

• Speedometer reads too fast: Driven gear has too few teeth — replace with one having more teeth
• Speedometer reads too slow: Driven gear has too many teeth — replace with one having fewer teeth
• Erratic readings: Check for worn gears, damaged cable, or incorrect gear housing
• No reading: Verify the drive gear is installed and the cable is connected properly

Frequently Asked Questions

• What drive gear does my 700R4 have? — Early 700R4s use 7-10 tooth drive gears; later models (1987+) use 15-25 tooth. Remove the speedometer housing to inspect.
• Can I change the drive gear? — Yes, but it requires removing the tail shaft housing and sometimes the output shaft. Most users change only the driven gear.
• What if my calculated gear isn't available? — Choose the closest available and use an inline correction adapter (Dakota Digital or similar).
• Do I need a different housing? — Some driven gear tooth counts require a specific housing. 700R4 housings are marked for gear range (34-39 teeth or 40-45 teeth).