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
new gears...will they affect speedometer?
- Thread starter Ted87GT
- Start date
poneypower89
Now everyone in the world will know I wanna bang t
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.
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
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.
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.
bill302
Active Member
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/
http://johnsmustang.com/Catalog/3230/
thegabrielles
Member
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
Michael Yount
Mustang Master
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
http://www.geocities.com/mgnedell/notchback/tech/speedo.html
http://ddperformance.com/speedo_gear_chart.htm
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.
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.
