speedometer gear

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90windsor

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what size speedo gear do i need?

i have 35 inch tires with 4.56 gears

it was originall 31 tires with 3.55

what is the stock speedo gear tooth count?

is it 19?

i really dont want to take it apart and count since i just replaced all those t-case seals. only way im taking it apart is if i find the right speedo gear and JBG only has them up to 21 tooth anyway

i used the equations in JBG and if it was a 19 it comes out to be about 21.7 something. so id need a 22 tooth? sound correct?

thanks

 
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MUZZALL

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Whats the equation you used? The gear is easy to pull it's just the one bolt on the tail housing and its O-ring sealed.

 

miesk5

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This is by my pal Chris B; Gear Change Calculator w/Ford Part Numbers, Colors, & Tooth Count

Source: by Chris B

To adjust for changing tire size:

Old tire x Old Gear / New Tire = New Gear

OT x OG / NT = NG

(some one told me that 31" tires usually has a 19 tooth gear, and 235/75/15 tires has a 21 tooth gear)

Example:

Old Tire - 29"

Old Gear - 19 tooth

New Tire - 33"

New Gear - ?

235/75/15 = 28.9"

If you change tire size and gears (or just gears), you have to go one step further:

New Gear / Old Ratio x New Ratio = New Gear

NG / OR x NR = NG

17 / 3.55 x 4.56 = 21.8

21 / 33.5" * 28.8" = 18.1

18 / 3.55 * 4.56 = 23.1

Each tooth on the speedo gear adjusts your speedometer reading by approx. 5%. So when you add a tooth, you reduce the speedometer reading by 5%.

See Chris's site to view more Color Codes, here is the 19 tooth as an example;

Ford (truck) Speedometer Gear's

Tooth Count Colour Part Number Notes

19 Pink C0DZ-17271-B

and by our pal Seabronc;

Gear Color Codes, 80 and up

Source: by JBG via Seabronc

and by Ryan

16 teeth - Wine- C0DZ-17271-A

17 teeth - WHT- C3DZ-17271-C

18 teeth - YEL - C0DD-17271-B

19 teeth - PNK - C0DZ-17271-B

20 teeth - BLK - C1DZ-17271-A

21 teeth - RED - C4OZ-17271-A

aprox $3 each at your local Ford dealer

First you need to search for a couple of numbers:

A) How many teeth are on the drive gear inside your transfer case? (possible options are 6, 7, or 8 teeth)

B) What is the axle gear ratio?

C) How many tire revolutions per mile? (Look on your tire manufacturers web site)

The formula for finding the correct speedo gear is:

drive gear x axle ratio x tire rev/mile

 

miesk5

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forgt to add this; I believe you can get gears w/22, 23 , etc teeth; this is by Chris B; "...Don't forget the 23 tooth gear (I think it is white). It is made by the aftermarket and available from gear shops and Mustang parts suppliers. I needed it when I ran 4.56's and 33's..."

and a reply by Ryan; "....The 23 tooth gear is Jeep part # J3167393

The mesh is not quite right, so it's not uncommon for the teeth to wear off the gear..."

Looked up one one-line source for you, TCI;

http://www.tciauto.com/Products/TechInfo/speedo_gears.asp

Driven Gears 23 teeth - white - Note; This is a retrofit gear to allow the speedometer to function with 3.73 and 4.10 rear end gears. Since the gear tooth pitch is slightly different than OE, the service life of this gear is limited to less than 25,000 miles.

TCI Part # is 881004 OEM # is J316-7393

http://www.tciauto.com/Products/components..._gears.asp#ford

 
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90windsor

90windsor

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thank you for the help. i needed a 21. just put it in today and it works good

 

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