My speedo is about 10mph too slow, and I'm not sure why. It's got 245/50/16 tires which are about the same height as the stock tires, I believe. I'm pretty sure the rear gears are stock as well. They feel like the stock 2.73s to me. Could my tires be throwing it off 10 mph?
Check it out - jack up the rear of the car - block the front wheels and make sure the car is secure - mark the tire with chalk and mark the drive shaft with chalk - spin the wheel and count the number of times the shaft spins to the wheel spins to find out what your gear really is - if it is stock then you can measure the height of the tire and factor that in to see if you need to adjust the driven gear a tooth or two - Ford dealers have gears in stock usually for $9 or so - to slow down the speedo go up in driven tooth count and to speed up the speedo go down in driven tooth count.
1 tooth usually equals about 4-5mph change
Check it out - jack up the rear of the car - block the front wheels and make sure the car is secure - mark the tire with chalk and mark the drive shaft with chalk - spin the wheel and count the number of times the shaft spins to the wheel spins to find out what your gear really is - if it is stock then you can measure the height of the tire and factor that in to see if you need to adjust the driven gear a tooth or two - Ford dealers have gears in stock usually for $9 or so - to slow down the speedo go up in driven tooth count and to speed up the speedo go down in driven tooth count.
1 tooth usually equals about 4-5mph change
i have the same problem but if my speedo says im going 70mph i am really going 85mph... and i have stock gears 2.73.. and when im doing 70mph so my speedo says im right at 2,000rpms... i have changed the speedo sensor and still same problem! anyone know??? dont mean to hijeck
sounds like you need to pull your speedo cable out of the trans - count the teeth on the driven gear and then see about getting a speedo driven gear 3 or 4 teeth less - for example - if a 20 tooth is in there now you would need a 16 tooth replacement it should bring that speedo up faster by about the right amount.