I bought my car used and noticed that my speedometer was off. I had someone drive next to me and I was going at least 10 mph slower than what it said on the speedometer. Anybody know why its off or if i can change it back to normal?

 

you might have different gears in it i just had 4.10's put in mine today mine does the same thing take it to the ford dealer they can do it for 80 bucks. Better then buying a $380 tuner.

 

Is there a way to check my car to see if its had new gears put in or what?

 

Anybody know?

 

what are your rpms at 70?

 

or you can take the diff cover off...drain all the oil...count the number or teeth on the ring gear and divide that by the number of teeth on the pinion gear...this gives you your ration....example...41/10 = 4.1....4.10:1 gear ratio

or do it with the lil computer calculator thing

 

My rpms were 2500 at 70mph on the speedometer. At the real 70mph, my rpms were about 3000 in 4th gear.