speedometer is off

[Dryer]

My speedometer is off by 15 mph. At 55 I'm actually going 71 or 72 mph. The rear end appears to be stock. Any ideas on other things to look for would be great!

 

[montecarlo-ts]

tire size would throw it off. i dont know what causes mine to be off but since i put in my last th350 the speedometer wont go over 45 even if im going 80. maybe something isnt hooked up right.

 

[Jg85350Regal]

You probably have the wrong speedo gear. Theres different tooth counts based on tire diameter and rear end gear ratio.
http://www.transmissioncenter.net/speed ... ____va.htm

 

[megaladon6]

what he said. what trans do you have? the 350 is easier to change/check the gears on. also, you need to find out what rear ratio you have. jack up the rear and put a chalk mark on a tire and the driveshaft. in neutral, rotate the driveshaft and count the turns it takes to get one tire rotation. this works best on a posi rear as both tires will turn. if it's a non posi, i believe you divide your result by 2. or you have to mark the shaft and slowly move the car, on the tires/ground, and have someone on the ground to count the turns. the safest way is to push the car on level ground.

 

[Doober]

You need a ~30% shorter drive/driven tooth ratio on your speedo gear 8)

http://www.transmissioncenter.net/speed ... ____va.htm