I was wondering if anyone knows much about the old speedometer gears on cars... I need a little help.

Anyways, my truck speedometer is off (slow) by 5-6 mph in town, and at highway speeds it's about 10mph slow. So when it says I'm driving 30mph, I'm really going about 25, and when it says I'm driving 70, I'm really going about 60. (I used the GPS to figure this out, along with speed radars they have in town)

Anyways, I need a new speedometer gear, and I currently have one with 22 teeth in it. I was wondering if anyone knows what amount of teeth I need in a new gear to make this accurate. I heard once that usually it's about 2mph per tooth in the gear, but don't know if this is true or not. I also don't know which way it goes, if I need more teeth or less to speed up my speedometer.

Any help would be GREATLY appreciated! Unfortunately most technicians don't know a whole lot about these old cars anymore..and the only guy I knew at a dealership that knew a bit about old cars worked at my dealer which closed....

Thanks again!!!!

 

found this online - a Gear Calculator....

http://www.sccoa.com/faq/speedgr.html

might help.

 

Thanks! Unfortunately that calculator doesn't quite work for me.... Doesn't go up to my tire size, and I don't know how many drive gears I have...only driven...

But thanks though!

 

Try contacting a Dyno shop.....

Cajun / Al