new gears...will they affect speedometer?

T

Ted87GT

Founding Member

Sep 21, 2001

58

0

6

Southern Maine

Mar 9, 2006

#1

• Mar 9, 2006

• #1

Im doing a ton of rear end work on my car (3.73 gears, install kit, trac.-lok rebuild kit). I havent changed the speedometer gear yet. Will the gears throw off my speedometer calibration? If yes, how will it read? Will the MPH on the gauge be higher or lower than it actually is, and by how much approximately? thanks

 

poneypower89

Now everyone in the world will know I wanna bang t

Dec 6, 2004

0

3

28

Indianapolis, Indiana

Mar 9, 2006

#2

• Mar 9, 2006

• #2

Yes, without changing the speedo gear your mph will be off...

I can remember exactly, but i think your speedo will read higher.... dont quote me on that one though.. someone will let you know for sure.

 

thegabrielles

Member

Feb 26, 2003

516

1

16

Atlanta Georgia

Mar 9, 2006

#3

• Mar 9, 2006

• #3

yep higher, if you went from 2.73 to 3.73 it will read about 25% higher, meaning if it says you are going 60, then you are around 45, if it says you are going 80 then you are going around 60. Now dont go speeding and tell the cop I told you that you were only going 60....

The speedo Gear is EASY to change adn should have been done with the gear swap by the shop that did the installation. I think a gear is about $10 and with a juck and a 10mm or 3/8 wrench you can change it out yourself.

 

M

mikemustang289

Member

Jan 12, 2006

224

0

16

mesa, az

Mar 9, 2006

#4

• Mar 9, 2006

• #4

speedo gear will read faster than you are going. you need a speedo gear with more teeth, a 19tooth gear should work but you'll have to check to make sure.

 

bill302

Active Member

Nov 2, 2005

2,131

1

46

alabama,gadsden

Mar 9, 2006

#5

• Mar 9, 2006

• #5

yes,your speedometer will read higher but you can fix it by installing a 21R tooth (red) speedo gear....which you can purchase on the link below...

http://johnsmustang.com/Catalog/3230/

 

thegabrielles

Member

Feb 26, 2003

516

1

16

Atlanta Georgia

Mar 9, 2006

#6

• Mar 9, 2006

• #6

Are you sure about teh 21 tooth gear? I have a 21 tooth in mine for 4.10 gear. Well at least I think I do. Please correct me if I am wrong.

 

bill302

Active Member

Nov 2, 2005

2,131

1

46

alabama,gadsden

Mar 9, 2006

#7

• Mar 9, 2006

• #7

thegabrielles said:

Are you sure about teh 21 tooth gear? I have a 21 tooth in mine for 4.10 gear. Well at least I think I do. Please correct me if I am wrong.

Click to expand...

you should have the 23 tooth white speedo gear...

 

Michael Yount

Mustang Master

Apr 10, 2002

9,039

6

79

Charlotte, NC

Mar 10, 2006

#8

• Mar 10, 2006

• #8

Your speedo will read faster than you are going. The error will be exactly the same as the ratio of the rear gear change -- 2.73 to 3.73 will throw the speedo off by about 35%. Check these links for how to correct the error.

http://www.geocities.com/mgnedell/notchback/tech/speedo.html
http://ddperformance.com/speedo_gear_chart.htm

 

jrichker

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Mar 10, 2000

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Dublin GA

Mar 10, 2006

#9

• Mar 10, 2006

• #9

The stock range of speedo gears work correctly with a limited range of tire sizes. The white 23 tooth gear seems to work good for some guys and it self destructs in a few months for others.

See http://www.corral.net/tech/gearcalc.html for more help

Check to see if there is a speedometer shop in your area. If there is, ask about the Stewart-Warner speedometer gearbox. I believe it is either a 777 Series Drive Joint Kits and Parts or 666 Series Drive Joint Kits and Parts. It is a small gear box that fits between the speedo pickup gear on the transmission and the speedometer. It has quick change gears that allow you to choose almost any tire size and rear end gear ratio you want. This will allow you to get the accuracy with within 1%-3%. The drawback is that it isn't cheap.
Please excuse the typo (their's, not mine) in the following picture - it should read Custom ratio adapters, not Custom radio adapters.

See http://www.gaugeguys.com/ratioadapt.htm for more info.