Speedometer Pinion Gear Transmission 18 Tooth

Depending on what rearend gear ratio you have will determine how many teeth are needed on the speedo gear. Here is a chart:

Gear Ratios

16 Teeth Gear: 3.36 Ratio
17 Teeth Gear: 3.54 Ratio
18 Teeth Gear: 3.70 Ratio
19 Teeth Gear: 3.90 Ratio

Datsun Models & Corresponding Diff Ratios (from factory)
240Z 70-73 MT (3.36) (R180)
240Z 70-73 MT 5spd. (3.90) (R180) - non US
240Z 71-73 Auto (3.54) (R180)

260Z 74 MT (3.36) (R180)
260Z 74 Auto (3.54) (R180)

280Z 75-76 (3.54) (R200)
280Z 77-78 MT (3.54) (R200)
280Z 77-78 Auto (3.54) (R180)

280ZX 79 MT,4 Spd,2 Seater (3.36) (R180)
280ZX 79 MT,5 Spd,2 Seater (3.36) (R180)
280ZX 79 All With Automatic(3.54) (R180)
280ZX 79 MT,4 Spd,4 Seater (3.36) (R200)
280ZX 79 MT,5 Spd,4 Seater (3.70) (R200)
280ZX-GL 79 (3.70) (R200)
280ZX 80 MT,2 Seater (3.54) (R180)
280ZX 80 Automatic 2/4Seat (3.54) (R180)
280ZX 80 MT,4 Seater (3.90) (R200)
280ZX-GL 80 (3.90) (R200)
280ZX 81-83 Automatic all (3.54) (R180)
280ZX 81-83 Turbo - all (3.54) (R200)
280ZX 81-83 MT (3.90) (R200)

Datsun 510: 1968 (3.70) (R160)
Datsun 510: 1969-1973 (3.90) (R160)