Question about speedometer gear

I have an aod in a 56 ford car - i put a cable in it with a 17 tooth gear on it. The speedometer reads 85 when I'm doing 65 should I get a gear with more or less teeth to get closer to right ? The ford dealer has gears with 14 to 21 teeth. I do not what gears the rear end has but they are low. I dont mind it being off a little, any ideas?

 

Anyone? I am going to buy a gear tomorrow either way. The parts guy at the dealership is not much help either, so even an oppion would be nice , less teeth or more teeth?

 

21.

 

You will need a driven gear (thats the one on the end of the cable) with more teeth to slow down the speedo. Drive gear (the one on the tail shaft) with less teeth will slow it down too.

 

Thanks guys , I will try the 21 tooth gear and see how close that gets me.

 

17 x 85 / 65 = 22 teeth, but you can only get a 21. should get you within a couple mph

 

Your speedometer is reading 30% fast, going to a 21 tooth will slow it down 20%. You will still be reading 10% fast. You will need a gear ratio adapter to get it right on the money.

 

pull the speedo. my '41 ford speedo was adjustable. went from stock 3.78's to 2.73's in a 9" and adjusted the speedo until it's within 1-2 MPH of being correct.

 

did you adjust the odometer too?

 

To correct the odometer I had to get the correct gear. But originally I adj. the speedo. Once I found out that worked I found a gear that made the odometer correct and readj. the speed.

 

And here we go again with one of those speedometer guys that have all the correct answers...

Take it to your local Speedometer shop and for a mere pitance they will fix you up in a jiffy. Cruisin down the road without the worry.

 

Well I'm pretty sure the nearest speedometer shop wouldn't quaifly as local. So I got the 21 tooth gear I just havn't put it in yet.

 

Cool,
Good luck! It should be close...

 

Quick up date, The gear is in and it seems very close, gonna have my wife pace me tomorrow and see how close it really is.

 

You can be off a bit and be okay, my daily beater I put tires on that are like 2 inches taller than it was supposed to come with and it seems to have made no difference, I drove by one of those things the cops put out that shows you your speed and I was right on the money.

 

Well after being pace when the spedo reads 68 Im doing 65 so thats good enough for me!