Overview
The Crown Automotive 4338996 is a speedometer drive gear for the NP231 transfer case. When tire size or axle gear ratio changes, the original speedometer gear stops reading true road speed, and the MPH reading runs high or low until the tooth count is matched to the new setup.
A tire and gear ratio chart is the usual way to work out the correct tooth count, so start there before choosing a gear.
Key features
- Speedometer drive gear designed for the NP231 transfer case
- Fits the NP231 transfer case as a replacement gear
- Corrects speedometer readings after tire size or axle gear changes
- Tooth count is chosen to match the new tire and gear setup
Choosing the right tooth count
Speedometer error comes from the relationship between tire rolling diameter, axle gear ratio and the number of teeth on the speedometer drive gear. A larger tire or a numerically lower axle ratio reduces the wheel turns per mile, so the speedometer can read low, and the opposite change makes it read high. Working through the numbers on a tire and gear ratio chart is the most reliable way to decide which tooth count brings the reading back in line.
Measure the actual tire height rather than relying on the sidewall, because worn or underinflated tires shift the result. Once you have a candidate tooth count, check the speed reading against a GPS reference at a steady speed. Keep the original gear so you can return to it if the new reading does not match your expectations.
- Measure the actual tire height
- Note the axle gear ratio before ordering
- Compare candidates on a tire and gear ratio chart
- Verify the reading with GPS after fitting
Specifications
| Brand | Crown Automotive |
|---|---|
| Part number | 4338996 |
| UPC | 848399003536 |
| Transfer case | NP231 |
| Gear type | Speedometer drive gear |
Vehicle fitment
The NP231 transfer case is the deciding factor for fit, so check it first.
Confirm your transfer case is an NP231, then make sure your vehicle’s year, model and trim match before ordering.
Installation notes
Work out the tooth count from a tire and gear ratio chart before fitting, because the gear that matches your tires may not be the stock one.
What’s included
Compare the package contents with your installation plan before starting.
