Speedometer gear

[JasonNC]

I changed the rear end in my 48 and now the speedometer is about 10 miles an hour too fast. I take it I need a different gear, but in looking over past threads about this subject it looks like the 18 tooth gear for an overdrive transmission and rear end for an eight cylinder are hard to come by. (My car is a six cylinder but the overdrive and transmission came from my Super 8 parts car.) Any help will be greatly appreciated.
Jason

[dave s]

What is your ratio rear end ratio and your tire size?

[JasonNC]

I have 15 inch tires on it and I'm assuming the ratio is what Walt Mordenti says in his book is correct for a 1948 with overdrive, i.e. 4:55.

[hudsonguy]

I have 15 inch tires on it and I'm assuming the ratio is what Walt Mordenti says in his book is correct for a 1948 with overdrive, i.e. 4:55.

Jason,

To check for sure, just jack up the back end and in neutral count the wheel revolutions versus driveshaft revolutions. If it's a 4:55, you'll get one revolution of the wheel for every 4.55 turns of the driveshaft.

[Nevada Hudson]

Al Saffrahn is our club expert on these, and has many different speedometer gears for sale at reasonabe prices. (520) 568-2911