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Author Topic:   Correct speedo cable driven gear
Gary
Gearhead

Posts: 713
From: Sarasota, Fla. USA
Registered: Jun 99

posted 07-03-2001 08:04 AM     Click Here to See the Profile for Gary   Click Here to Email Gary     Edit/Delete Message   Reply w/Quote
Id like to double check my findings:
(6) tooth gear in trans.
Final rear ratio 3.90
Tire dia. 31"

How many tooth gear do I need for the end of my speedo cable for correct mph readings?

I came up with 15.22
Is this correct?
I think I should order a 15 tooth 3A gear for my 4sp. manual--right?

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svt522
Journeyman

Posts: 53
From: Hampton, Va
Registered: Jul 2001

posted 07-03-2001 08:19 PM     Click Here to See the Profile for svt522   Click Here to Email svt522     Edit/Delete Message   Reply w/Quote
Check out the following site!

http://www.bgsoflex.com/speedo1.html

------------------
svt522
1996 SVT Cobra (#522)
1967 F100 351C
1973 "Q" Code Mach1

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SteveLaRiviere
Administrator

Posts: 31026
From: Saco, Maine
Registered: May 99

posted 07-03-2001 09:03 PM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Gary:
Id like to double check my findings:
(6) tooth gear in trans.
Final rear ratio 3.90
Tire dia. 31"

To figure tire revolutions per mile:

63360/[tire diameter x PI]

63360/31 x 3.14156 = 63360/97.388 = 650.59 rev. per mile.

A 31" tires revolves 650.59 times per mile.

So,

Driven gear=[drive gear][axle ratio][tire rev .per mile]/1000

Driven gear=[6][3.90][650.59]/1000

Driven gear= 15223.806/1000 = 15.22

So you are right on, Gary.

------------------
'70 Mustang Mach 1 M code 351C 4V/FMX/3.25 open
'72 Mustang Sprint Coupe 351C 4V/FMX/4.30 Trac Lok
'94 F-150 XL 5.8L/E4OD/3.55 Limited Slip
'97 Probe GTS 2.5L DOHC {Wife's car...}
All Fords since 1977

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