jgordon

when i bought my stang the dealer said it was bone stock.after a couple weeks,the diff cover was leaking,took it back to dealer for repair,and i watched as they took the cover off,to see it has 3.73 gears,i know stock gears is 3.27,my speedometer reads 10mph slow,can you tell me how to make it right?also my rpms are 2000 at 70mph? i know that dont sound right.i ckecked my mph with the odometer in test mode,would the test mode be right?

Goldenpony

I know what you are talking about. Actually it looks like you're writing about a 2001 Mustang. I had a 2000 GT and had 3.73 gears installed and had the same problem. I tried taking it to Ford and they said they couldn't set any gear ration that wasn't offered from the factory. I don't think your odometer test mode will work either since the computer still thinks you have 3.27 gears. If I remember right, they (Ford dealer) changed the computer setting to different size wheels which reduced the speedo error but didn't eliminate it.

jgordon

should my speedometer be reading fast instead of slow?would my tach be reading right?

Goldenpony

I believe your speedo will be reading too high. Your tach should be reading OK.

jgordon

my speedometer is reading 10mph slow.so if should be reading fast?

candymanjl

if your speedo is calibrated for the stock 3.31 rear end ratio and you have 3.73's then the speedo will read faster than what you're actually going. now if you went from 3.73's to the stock 3.31's then you would be going faster than what the speedo says.

jgordon

my speedometer is reading 10mph slow,so its doing the opposite.

jgordon

thats not making sense why my speedo is reading slow,right?