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Speedometer Gear Usage Chart

The document provides a speedometer gear usage chart for 7.5" and 8.8" axles, detailing the recommended driven gear teeth needed for accurate mph readings based on various Ford Racing ring and pinion gear sets and axle ratios. It includes notes on specific applications and tire sizes, as well as part numbers for speedometer drive and driven gears available from Ford and Lincoln dealers. Additionally, a calculation example is provided for determining the required driven gear teeth if the axle/tire combination is not listed in the chart.

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panninilton
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40 views1 page

Speedometer Gear Usage Chart

The document provides a speedometer gear usage chart for 7.5" and 8.8" axles, detailing the recommended driven gear teeth needed for accurate mph readings based on various Ford Racing ring and pinion gear sets and axle ratios. It includes notes on specific applications and tire sizes, as well as part numbers for speedometer drive and driven gears available from Ford and Lincoln dealers. Additionally, a calculation example is provided for determining the required driven gear teeth if the axle/tire combination is not listed in the chart.

Uploaded by

panninilton
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Speedometer gear usage chart — 7.5" and 8.

8" axle
The chart specifies the driven gear Speedometer Driven Gear Teeth
recommended to obtain approximately Drive Gear Teeth
correct mph readings when the listed Ford Axle Ratio 6T 7T ➀ 8T ➁
Racing ring and pinion gear sets are used in
3.08 – 18 20 NOTES: ➀ Used in most vehicles with V8 and
conjunction with the indicated speedometer
3.27 16 19 21 T-5 trans­mis­sions from 1983-1989
drive gear and Mustang original equipment.
and 1996-1998 Cobra with
15"/16"/17" tires (800-815 revolutions/ 3.45/3.55 17 20 – T-45 transmissions.
mile). A dash in the chart in­di­cates that
3.73 18 21 – ➁ Used on 1990-1995 Mustang V8 with T-5
particular combination cannot be obtained.
4.10 20 – – transmissions and 1996-1998 Mustang
If you are using oversize/un­der­size tires,
GT with T-45 transmissions.
obtain the rev­o­lu­tions/mile information from 4.30 21 – – ➂ Discontinued.
the tire manufacturer and plug it into the
formula below. The part numbers of the T-5 Manual Trans. Drive Gears Manual Trans. Driven Gears Auto Trans. Driven Gears
various speedometer drive and driven gears (17285) (17271) (17271)
are shown in the charts. The gears can be Number Service Number Service Number Ser­vice
ob­tained from any Ford and Lincoln dealer. of Part of Part of Part
teeth Color Number teeth Color Number teeth Color Number
They are not available from Ford Racing.
The drive gears on T-5/T-45/SROD/ 6 Black E3ZZ-B 16 Wine C0DZ-A 16 Blue D0AZ-A ➂
Tremec® manual trans­mis­sions can be 7 Yellow E3ZZ-A 17 White C3DZ-C 17 Green C7SZ-A
changed. The drive gear on Ford rear-wheel 8 Green F0ZZ-A 18 Yellow C0DD-B 18 Gray C7SZ-B ➂
automatic transmissions is ma­chined into T-45 Manual Trans. Drive Gears 19 Pink C0DZ-B 19 Tan C7VY-A
the output shaft. Chang­ing the drive gear (17285) 20 Black C1DZ-A 20 Orange C8SZ-B
is im­prac­ti­cal since it requires a new
output shaft and trans­mis­sion teardown. 7 F6ZZ-AA 21 Red C4OZ-A 21 Purple D0OZ-B
Most have 7 or 8 teeth. 8 F6ZZ-BA

special applications driven gear calculation example


Step 1 Step 2 Step 3
If your axle/tire combination is not in the • T-5 Trans. You would select driven gear with closest
above charts, you can calculate the number • Drive Gear Teeth = 7 whole number of teeth, which would be
of teeth required on the driven gear by using • Axle Ratio = 3.73 the 21-tooth C40Z-17271-A part.
this formula: • Tire Rev. Per Mile = 815 (225/60 VR15)
Driven Gear Teeth = Drive Gear Teeth x Axle Ratio x Tire Rev. Per Mile = 7 x 3.73 x 815 = 21.3 (driven gear teeth)
1000 1000

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