| 1971 Firebird Speedometer Gear usage Chart | |||||||||||||
| Driven Gear Or Sleeve | Tire Size | Speedometer Adapter | |||||||||||
| Rear End Ratio | Part # | Teeth | Color | F60 X 15 | F78 X 14 | F70 X 14 | E78 X 14 | Model | Ratio | Part # | Color | Trans Code | Drive Gear Teeth |
| 3.42 | 3987922 | 22 | GRAY | X | X | WT-WO | 8 | ||||||
| 3.42 | 3987921 | 21 | RED | X | X | WT-WO | 8 | ||||||
| 3.73 | 3987917 | 17 | PURPLE | X | X | X | X | 6477964 | WT-WO | 8 | |||
| Information supplied by George Pearson, taken from a Pontiac Parts Book | |||||||||||||