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| = Overview = | = Overview = | ||
| Stock 1200 Speedometer gear ratio: | Stock 1200 Speedometer gear ratio: | ||
| - | * pinion teeth/worm teeth on trans output shaft | + | pinion teeth/worm teeth on trans output shaft |
| * 17/5 (3.90 diff) | * 17/5 (3.90 diff) | ||
| - | * 18/5 for Wagon or Ute (4.11 diff) | + | * 18/5 (4.11 diff) for Wagon or Ute |
| - | [http://i297.photobucket.com/albums/mm219/ddgonzal/Datsun%201200/wiki/19T.jpg http://i297.photobucket.com/albums/mm219/ddgonzal/Datsun%201200/wiki/th_19T.jpg] [http://datsun1200.com/modules/myalbum/photo.php?lid=15669 http://datsun1200.com/uploads/thumbs/15669.jpg] | + | [http://datsun1200.com/modules/myalbum/photo.php?lid=15669 http://datsun1200.com/uploads/thumbs/15669.jpg] [http://i297.photobucket.com/albums/mm219/ddgonzal/Datsun%201200/wiki/19T.jpg http://i297.photobucket.com/albums/mm219/ddgonzal/Datsun%201200/wiki/th_19T.jpg] |
| To adjust the speedometer for different diameter tires, change the transmission cable pinion cog. | To adjust the speedometer for different diameter tires, change the transmission cable pinion cog. | ||
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| Given that stock is a 17 tooth pinion, moving to one more or less tooth is about 6% change. So by changing the pinion you can only get it to ±3 mph accurate. For example, at 100 mph, within 3 mph. Or at the standard 50 mph rating, a reading between 1½ mph (48½ to 51½) is the best you can hope for. For finer tuning the speedometer itself needs calibration. Or you could fit different diameter rear tires. | Given that stock is a 17 tooth pinion, moving to one more or less tooth is about 6% change. So by changing the pinion you can only get it to ±3 mph accurate. For example, at 100 mph, within 3 mph. Or at the standard 50 mph rating, a reading between 1½ mph (48½ to 51½) is the best you can hope for. For finer tuning the speedometer itself needs calibration. Or you could fit different diameter rear tires. | ||
| - | EXAMPLE: If you are reading say 60 when you are really going 50 then the speedo cable needs to slow down by about 20% to read more accurately. If the speedo drive has a 17 tooth cog in it try to find a cog that reduces by 20%. 17 X .20 = 3.4 teeth... 17 + 3.4 = 20.4 teeth, the closest is a 20 tooth cog. | + | EXAMPLE: If you are reading say 60 when you are really going 50 then the speedo cable needs to slow down by about 20% to read more accurately. If the speedo drive has a 17 tooth cog in it try to find a cog that reduces by 20%. 17 X .20 = 3.4 teeth... 17 + 3.4 = 20.4 teeth, the closest is a 20 tooth cog.<table width=50% bordercolor=black border=1> |
| - | + | ||
| - | <table width=50% bordercolor=black border=1> | + | |
| <tr bgcolor=ccccff><td>Teeth</td><td>% change</td><td>50 mph reading</td></tr> | <tr bgcolor=ccccff><td>Teeth</td><td>% change</td><td>50 mph reading</td></tr> | ||
| <tr><td>16</td><td>106.25%</td><td>53.1</td></tr> | <tr><td>16</td><td>106.25%</td><td>53.1</td></tr> | ||
| <tr><td>17</td><td>100.00%</td><td>50.0</td></tr> | <tr><td>17</td><td>100.00%</td><td>50.0</td></tr> | ||
| <tr><td>18</td><td>94.44%</td><td>47.2</td></tr> | <tr><td>18</td><td>94.44%</td><td>47.2</td></tr> | ||
| - | <tr><td>19</td><td>89.47%</td><td>44.7</td></tr> | + | <tr><td>19</td><td>89.47%</td><td>44.7</td></tr></table> |
| - | </table> | + | |
| - | + | ||
| - | Correction Table, increase Teeth by: | + | <br>Correction Table, increase Teeth by:<table border=1 cellspacing=0 width=100%> |
| - | <table border=1 cellspacing=0 width=100%> | + | |
| <tr bgcolor=ccccff><td> Actual mph</td><td> Desired mph</td><td> Tooth </td></tr> | <tr bgcolor=ccccff><td> Actual mph</td><td> Desired mph</td><td> Tooth </td></tr> | ||
| <tr><td> 40 </td><td> 50 </td><td> 3+ </td></tr> | <tr><td> 40 </td><td> 50 </td><td> 3+ </td></tr> | ||
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| </table> | </table> | ||
| - | Estimated Tire Correction Table (for 3.9 diff) | + | <br>Estimated Tire Correction Table (for 3.9 diff)<table border="1"> |
| - | <table border="1"> | + | |
| <tr bgcolor="ccccff"><td> Size </td><td> Diameter </td><td> Difference </td><td> Pinion </td><td> ~Error </td></tr> | <tr bgcolor="ccccff"><td> Size </td><td> Diameter </td><td> Difference </td><td> Pinion </td><td> ~Error </td></tr> | ||
| <tr><td> 165/55R12 </td><td> 19.1 </td><td> 88% </td><td> 19T </td><td> 0% </td></tr> | <tr><td> 165/55R12 </td><td> 19.1 </td><td> 88% </td><td> 19T </td><td> 0% </td></tr> | ||
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| <tr><td> 185/60R15 </td><td> 23.7 </td><td> 109% </td><td> 16T/15T </td><td> 3% </td></tr> | <tr><td> 185/60R15 </td><td> 23.7 </td><td> 109% </td><td> 16T/15T </td><td> 3% </td></tr> | ||
| <tr><td> 205/40R18 </td><td> 24.5 </td><td> 112% </td><td> 15T </td><td> 0% </td></tr> | <tr><td> 205/40R18 </td><td> 24.5 </td><td> 112% </td><td> 15T </td><td> 0% </td></tr> | ||
| - | <table> | + | <table> |
| + | <br> | ||
| = Part Numbers = | = Part Numbers = | ||
| NOTE: while they are color-coded, order by part number, not by color. For example, 63-series and 56-series cogs (pinion gears) use different color coding. | NOTE: while they are color-coded, order by part number, not by color. For example, 63-series and 56-series cogs (pinion gears) use different color coding. | ||
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| Different transmission have different methods: | Different transmission have different methods: | ||
| - | Jeep - offset holder is rotated to various positions for each gear | + | * Jeep - offset holder is rotated to various positions for each gear |
| - | GM TH350 - two drive gears, each works with a range of driven gears | + | * GM TH350 - two drive gears, each works with a range of driven gears |
| - | 720 - all have 6T drive gear | + | * Nissan 720: all have 6T drive gear |
| - | 56-series, 60, driven gear is machined on the shaft | + | * Nissan 56-series, 60: driven gear is machined on the shaft |
| - | 4W63, 71B, 71C replaceable gear | + | * Nissan 4W63, 71B, 71: replaceable gear |
| = Ratio Adapter Box = | = Ratio Adapter Box = | ||
Revision as of 07:19, 17 May 2015
The speedometer reading is adjustable via the various drive gears fitted at the transmission. Depending on which final gear ratio (differential gears) are fitted, the speedometer gears are changed to keep the speedometer accurate.
Contents |
Overview
Stock 1200 Speedometer gear ratio:
pinion teeth/worm teeth on trans output shaft * 17/5 (3.90 diff) * 18/5 (4.11 diff) for Wagon or Ute
To adjust the speedometer for different diameter tires, change the transmission cable pinion cog.
* If speedo reads too fast, fit a bigger cog * If speedo reads too slow, fit a smaller cog
Given that stock is a 17 tooth pinion, moving to one more or less tooth is about 6% change. So by changing the pinion you can only get it to ±3 mph accurate. For example, at 100 mph, within 3 mph. Or at the standard 50 mph rating, a reading between 1½ mph (48½ to 51½) is the best you can hope for. For finer tuning the speedometer itself needs calibration. Or you could fit different diameter rear tires.
EXAMPLE: If you are reading say 60 when you are really going 50 then the speedo cable needs to slow down by about 20% to read more accurately. If the speedo drive has a 17 tooth cog in it try to find a cog that reduces by 20%. 17 X .20 = 3.4 teeth... 17 + 3.4 = 20.4 teeth, the closest is a 20 tooth cog.| Teeth | % change | 50 mph reading |
| 16 | 106.25% | 53.1 |
| 17 | 100.00% | 50.0 |
| 18 | 94.44% | 47.2 |
| 19 | 89.47% | 44.7 |
Correction Table, increase Teeth by:
| Actual mph | Desired mph | Tooth |
| 40 | 50 | 3+ |
| 43 | 50 | 2+ |
| 47 | 50 | 1+ |
| 50 | 50 | 0+ |
Estimated Tire Correction Table (for 3.9 diff)
| Size | Diameter | Difference | Pinion | ~Error |
| 165/55R12 | 19.1 | 88% | 19T | 0% |
| 165/60R12 | 19.8 | 91% | 18T | -2% |
| 165/70R12 | 21.1 | 97% | 17T | 3% |
| 155/80R12 | 21.8 | 100% | 17T | 0% |
| 175/70R13 | 22.6 | 104% | 16T | 2% |
| 195/50R15 | 22.7 | 104% | 16T | 2% |
| 165/70R14 | 23.1 | 106% | 16T | 0% |
| 205/45R17 | 23.5 | 108% | 16T | -2% |
| 185/60R15 | 23.7 | 109% | 16T/15T | 3% |
| 205/40R18 | 24.5 | 112% | 15T | 0% |
