Hey guys, its been a while because I've been off at college but im back on break now. My question: My speedometer gauge is off, the faster i go the more off it is. when im going 50 it reads 65 and when im going 60 it reads about 80mph. My odometer is also way too fast. I bought the car with non original rims and for all i know there could be a different rear end in it so it may have different gears. So does this sound like i have the wrong speedo gear in the tranny? How do i go about checking that? Can i do it with basic tools?

I have a 74 road runner with an auto 318. I think the gears are either a 3.55 or 3.23. The rims are i think 14 or 15" cragars.

 

Here are some.

http://www.mymopar.com/speedometer.htm

http://enthusiast.yearone.com/faqs/t...do-gear-chart/

http://www.transmissioncenter.org/sp...e_and_jeep.htm

 

Mark the tire & driveway rotate one full turn & mark Then measure That will give you the tire dia. Then Jack up one side OR BOTH if you have a sure grip. Rotate the tire again one revolution While counting the turne of the drive shaft That will give you the gear ratio.. Then look in the charts for the speedo gear you need Replace the seal & O ring gasket Put a light coat of silicon gasket maker on the O ring. Install it, wipe off the excess and let it sit over night if possible before adding fluid

I would guess 3.55 gears from your reading

 

Okay I took the tranny gear out and it was a red one with 26 teeth on it. I spun my tire around 2 times and the drive shaft rotated about 3.2 times so I think its 3.23 gears. I have an open differential. My tire says p245/60SR14 I have 14" rims. If my math is right I have 24.6 inch in diameter tires so I would need a 33 tooth gear. Is this right? I would want to make it so it read either exactly on or 1 or 2mph over so I don't get too many tickets. Does a 33 tooth gear sound right?

 

33 will probably be very close to what you want