| 1968 Fullsize Speedometer Gear usage Chart | ||||||||||||||||
| Driven Gear Or Sleeve | Tire Size | Speedometer Adapter | ||||||||||||||
| Rear End Ratio | Part # | Teeth | Color | 8.25 X 14 | 8.55 X 14 | 8.85 X 14 | 215R X 14 | 8.45 X 15 | H70 X 15 | 9.00 X 15 | Model | Ratio | Part # | Color | Trans Code | Drive Gear Teeth |
| 3.42 | 3987920 | 20 | BLUE | X | X | X | X | X | FM | 8 | ||||||
| 3.42 | 3860342 | 19 | NATURAL | X** | 6660-AJ | .9705 | 9777006 | RED | FM | 8 | ||||||
| 3.55 | 3860344 | 21 | RED | X | X | X | X | X | FM | 8 | ||||||
| 3.55 | 3987920 | 20 | BLUE | X** | FM | 8 | ||||||||||
| 3.73 | 3860342 | 19 | NATURAL | X | X | X | X | X | 666-AJ | .8653 | 9775436 | BLUE | FM | 8 | ||
| 3.73 | 3860344 | 21 | RED | X** | FM | 8 | ||||||||||
| 4.11 | 9780522 | 18 | GREEN | X | X | 6660-AJ | .9705 | 9777006 | RED | FN | 6 | |||||
| 4.11 | 9780522 | 18 | GREEN | X | X | X | FN | 6 | ||||||||
| 4.11 | 9780523 | 17 | BLACK | X** | 6660-AJ | .9705 | 9777006 | RED | FN | 6 | ||||||
| NOTE: X** = ADAPTER REQUIRED WITH POLICE OPTION | ||||||||||||||||
| Information supplied by George Pearson, taken from a Pontiac Parts Book | ||||||||||||||||