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Speedometer Pinion Differences

This writeup is meant to assist someone who is trying to correct their speedometer after changing their differential to a new final drive ratio, or after changing their transmission.Correcting your speedometer after putting different-sized tires on your car is beyond the scope of this writeup, and therefore will not be discussed except for this note: With a little math, it may be possible to use this writeup to get your speedometer a little closer, if not precise, depending on what tire size you've chosen.

image: Speedometer Pinion units

How the Speedometer Works

The speedometer and odometer are cable-driven by a pinion gear located on the right side of the transmission’s rear. This gear meshes directly with the transmission’s output shaft.

Pinion gears come in 16–23 teeth variations, each matched to differentials (assuming correct tire size). They are color-coded for easy identification.

⚠️ Important: If you use a pinion with 20+ teeth, you must replace the sleeve that holds it. These offset sleeves are required to prevent damage to both the pinion and the transmission drive gear.

Speedometer Pinion Gear Table

Pinion gears are color-coded and matched to differential ratios. For gears with 20+ teeth, an offset sleeve is required. Not using it may damage both the pinion and transmission drive gear.

| # Teeth | Color | Differential Ratio | Part Number | |---|---|---|---| | 16 | Yellow | 3.36 | |

84–86 Turbo

32703-78101)84–87 NA, 87–89 Turbo

32703-78102)88–89 NA

32703-78103)32703-78104)32702-58S21 32707-58S00## Modification Examples

Scenario: You bought an aftermarket 4.11 differential because you’re shooting for 12’s on stock fuel. You don’t mind the high revs, but your speedometer now reads too high, and your odometer is racking up miles too quickly.

Solution: Order the 20-tooth (Red) pinion gear and install it into your transmission. Viola! Your speedo is accurate again.

Scenario: You swapped a T5 transmission (84–86 Turbo) into your ’86 NA after your original transmission blew. The T5 came with a 3.54 differential, meaning the pinion gear is a 17-tooth (Black).

Problem: Your NA’s differential is 3.70, which requires an 18-tooth (Blue) pinion gear.

Solution: Conveniently, the correct 18-tooth gear can be taken from your old NA transmission and installed in the T5.

Sources Used

Based off a post from By WindigoZ 04/01/03 on Z31.com
1984-1989 Nissan Factory Service Manual