'79-'91 RX-7 (cable driven) Speedometer Correction Info
Chevy- Powerglide / T-350 / T-400 / 2004R / 700R4 / T-5 5spd
Ford- C4 / C6 / AOD / T-5 5spd
'79-'91 RX-7 (cable driven) Speedometer Correction Info
Chevy- Powerglide / T-350 / T-400 / 2004R / 700R4 / T-5 5spd
Ford- C4 / C6 / AOD / T-5 5spd
In years past, there has been much confusion when re-calibrating the RX-7 / V-8 speedo, as the standards for US speedos are different than that used by Mazda for the RX-7. Because of this, most speedo correction formulas and on-line calculators use the US standard and come up with the wrong answer. The calculation below will determine the proper combination of drive and driven gear sizes for your RX-7 V-8 conversion's 1025 rev/mi speedometer...
We use a specially fabricated speedometer "extension cable" that allows your existing RX-7 speedometer cable to connect to your Chevy or Ford transmission's mechanical speedometer output. This method allows enough room between the transmission speedo output and transmission tunnel's wall for maximum cable "bend radius" for long cable life. Speedometer calibration is accomplished by changing externally accessible "driven gears" to one with the correct tooth count.
Below we have listed the correct drive/driven gear combinations based on gear ratio and tire size. Just scroll down to the transmission for your application.
Chevy Turbo 350 & T5 5spd
The Turbo 350 and Borg Warner T-5's speedometer drive gears are located on the transmission's tailshaft, and can be changed with the transmission in the car by removing the tailhousing.
Here is a list of the suggested Chevy T-350 & T5 drive gear choices for your RX-7...
...7 tooth pink
Here is a list of the suggested T-350 & T5 5spd driven gear choices for your RX-7...
...18 tooth brown
...19 tooth natural
...20 tooth blue
...21 tooth red
...22 tooth grey
Here is a list of the suggested T-350 & T5 5spd gear combinations by tire diameter and axle ratio...
25" tire...
......3.90 rear gear ratio...7 tooth pink speedo drive gear / 21 tooth red speedo driven gear
......4.10 rear gear ratio...7 tooth pink speedo drive gear / 22 tooth grey speedo driven gear (close as possible)
26" tire...
......3.90 rear gear ratio...7 tooth pink speedo drive gear / 21 tooth red speedo driven gear
......4.10 rear gear ratio...7 tooth pink speedo drive gear / 22 tooth grey speedo driven gear
27" tire...
......3.90 rear gear ratio...7 tooth pink speedo drive gear / 20 tooth blue speedo driven gear
......4.10 rear gear ratio...7 tooth pink speedo drive gear / 21 tooth red speedo driven gear
28" tire...
......3.90 rear gear ratio...7 tooth pink speedo drive gear / 19 tooth natural speedo driven gear
......4.10 rear gear ratio...7 tooth pink speedo drive gear / 20 tooth blue speedo driven gear
29" tire...
......3.90 rear gear ratio...7 tooth pink speedo drive gear / 18 tooth brown speedo driven gear
......4.10 rear gear ratio...7 tooth pink speedo drive gear / 19 tooth natural speedo driven gear
2004R
The 2004R driven gear is located on the end of the governor assembly, and can be changed with the transmission in the car by simply removing the govenor.
Here is a list of the suggested 2004R drive gear choices for your RX-7...
...10 tooth green
Here is a list of the suggested 2004R driven gear choices for your RX-7...
...27 tooth black
...28 tooth yellow
...29 tooth green
...30 tooth blue
...31 tooth white
Here is a list of the suggested 2004R gear combinations by tire diameter and axle ratio...
25" tire...
......3.90 rear gear ratio...10 tooth grey speedo drive gear / 31 tooth white speedo driven gear
......4.10 rear gear ratio...10 tooth grey speedo drive gear / 31 tooth white speedo driven gear (close as possible)
26" tire...
......3.90 rear gear ratio...10 tooth grey speedo drive gear / 29 tooth green speedo driven gear
......4.10 rear gear ratio...10 tooth grey speedo drive gear / 31 tooth white speedo driven gear
27" tire...
......3.90 rear gear ratio...10 tooth grey speedo drive gear / 28 tooth yellow speedo driven gear
......4.10 rear gear ratio...10 tooth grey speedo drive gear / 30 tooth blue speedo driven gear
28" tire...
......3.90 rear gear ratio...10 tooth grey speedo drive gear / 27 tooth black speedo driven gear
......4.10 rear gear ratio...10 tooth grey speedo drive gear / 29 tooth green speedo driven gear
29" tire...
......3.90 rear gear ratio...11 tooth orange speedo drive gear / 29 tooth green speedo driven gear
......4.10 rear gear ratio...10 tooth grey speedo drive gear / 28 tooth yellow speedo driven gear
700R4 & Turbo 400
The 700R4 and Turbo 400's speedometer drive gears are located on the transmission's tailshaft, and can be changed with the transmission in the car by removing the tailhousing.
Here is a list of the suggested 700R4 & T-400 drive gear choices for your RX-7...
...15 tooth grey
Here is a list of the suggested 700R4 & T-400 driven gear choices for your RX-7...
...40 tooth black
...41 tooth yellow
...42 tooth green
...43 tooth purple
...44 tooth dark grey
...45 tooth lite blue
Here is a list of the suggested 700R4 and T-400 gear combinations by tire diameter and axle ratio...
25" tire...
......3.90 rear gear ratio...15 tooth grey speedo drive gear / 45 tooth lite blue speedo driven gear (close as possible)
......4.10 rear gear ratio...15 tooth grey speedo drive gear / 45 tooth lite blue speedo driven gear (close as possible)
26" tire...
......3.90 rear gear ratio...15 tooth grey speedo drive gear / 44 tooth dark grey speedo driven gear
......4.10 rear gear ratio...15 tooth grey speedo drive gear / 45 tooth lite blue speedo driven gear
27" tire...
......3.90 rear gear ratio...15 tooth grey speedo drive gear / 43 tooth purple speedo driven gear
......4.10 rear gear ratio...15 tooth grey speedo drive gear / 45 tooth lite blue speedo driven gear
28" tire...
......3.90 rear gear ratio...15 tooth grey speedo drive gear / 41 tooth yellow speedo driven gear
......4.10 rear gear ratio...15 tooth grey speedo drive gear / 43 tooth purple speedo driven gear
29" tire...
......3.90 rear gear ratio...15 tooth grey speedo drive gear / 40 tooth black speedo driven gear
......4.10 rear gear ratio...15 tooth grey speedo drive gear / 42 tooth green speedo driven gear
Ford C4 / C6 / AOD / T5 5spd
The Ford automatic's speedometer drive gears are cut into the transmission's tailshaft, and can not be changed easily. The T5 does have changable drive gears. For the automatic applications, a tooth count should be performed to determine your starting point.
Here is a list of the suggested Ford's T-5 drive gear choices for your RX-7...
...6 tooth black
...7 tooth black ('83-'89 T5)
...8 tooth green ('90-'95 T5)
Here is a list of the suggested Ford driven gear choices for your RX-7...
...16 tooth......wine (manual)......blue (automatic)
...17 tooth......white (manual)......green (automatic)
...18 tooth......yellow (manual)......grey (automatic)
...19 tooth......pink (manual)......tan (automatic)
...20 tooth......black (manual)......orange (automatic)
...21 tooth......red (manual)......purple (automatic)
...23 tooth......white (manual only- non-ford part with short lifespan)
Here is a list of the suggested Ford gear combinations by tire diameter and axle ratio for the transmissions that use a 7 tooth speedo drive gear...
25" tire...
......3.90 rear gear ratio...7 tooth speedo drive gear / 21 tooth speedo driven gear
......4.10 rear gear ratio...7 tooth speedo drive gear / 23 tooth speedo driven gear
26" tire...
......3.90 rear gear ratio...7 tooth speedo drive gear / 21 tooth speedo driven gear
......4.10 rear gear ratio...7 tooth speedo drive gear / 23 tooth speedo driven gear
27" tire...
......3.90 rear gear ratio...7 tooth speedo drive gear / 20 tooth speedo driven gear
......4.10 rear gear ratio...7 tooth speedo drive gear / 21 tooth speedo driven gear
28" tire...
......3.90 rear gear ratio...7 tooth speedo drive gear / 19 tooth speedo driven gear
......4.10 rear gear ratio...7 tooth speedo drive gear / 20 tooth speedo driven gear
29" tire...
......3.90 rear gear ratio...7 tooth speedo drive gear / 18 tooth speedo driven gear
......4.10 rear gear ratio...7 tooth speedo drive gear / 19 tooth speedo driven gear
Here is a list of the suggested Ford gear combinations by tire diameter and axle ratio for the transmissions that use a 8 tooth speedo drive gear...
25" tire...
......3.90 rear gear ratio...8 tooth speedo drive gear / 23 tooth speedo driven gear (close as possible w/o a correction gearbox)
......4.10 rear gear ratio...8 tooth speedo drive gear / 23 tooth speedo driven gear (close as possible w/o a correction gearbox)
26" tire...
......3.90 rear gear ratio...8 tooth speedo drive gear / 23 tooth speedo driven gear (close as possible w/o a correction gearbox)
......4.10 rear gear ratio...8 tooth speedo drive gear / 23 tooth speedo driven gear (close as possible w/o a correction gearbox)
27" tire...
......3.90 rear gear ratio...8 tooth speedo drive gear / 23 tooth speedo driven gear
......4.10 rear gear ratio...8 tooth speedo drive gear / 23 tooth speedo driven gear (close as possible w/o a correction gearbox)
28" tire...
......3.90 rear gear ratio...8 tooth speedo drive gear / 21 tooth speedo driven gear
......4.10 rear gear ratio...8 tooth speedo drive gear / 23 tooth speedo driven gear
29" tire...
......3.90 rear gear ratio...8 tooth speedo drive gear / 21 tooth speedo driven gear
......4.10 rear gear ratio...8 tooth speedo drive gear / 21 tooth speedo driven gear
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