i bought my mustang about a month ago, 2000 gt. the spedometer shows about 10mph faster than im actually going. does anyone have a solution to fix this?

 

You will need a diablo sport predator.

On the contrary, My guess is someone already dialed in a code from this unit to accommodate larger wheels or there could be a chip installed already. (Diablo sport, super chips)

 

but it has 17'', arent those factory?

 

Yes but previous owner could have had larger rims on (18in+), and put the stock rims back on when he/she sold it to you and didn't retune the speedo.

 

thanks guys

 

Yes. This is pretty likely. If the speedometer was having factory internal problems, you would see other symptoms and errors.

No joke: some 00 GT's came with 16 inch wheels but most came with 17 inch. Even if you just upgraded to and 18 inch wheel, you would throw your speedometer off. (Unlike the new ones) that is why you would need a programmer to correct the speedo.

I would just ask the person you bought it from. He definitely used a programmer on that car.

 

How about rear gears?

 

Correct. But its not as noticeable depending on ratio.

Plus a gear swap is fairly costly and most people put the money first in exterior mods. Either one will throw the speedo off.

I'd get the predator anyway to redefine/firm shift points and other mods that the OP may want in the future.

The factory tune is loaded in the unit as well.

 

Search for a shop that will calibrate you speedo. It shouldnt cost that much and they can calibrate it correctly.

 

i would ask the guy but i bought it from a dealer and they probally wont give me his number lol. i have a mechanic looking at it this weekend so i ask him about it

 

Agree that the dealer is unlikely to give out his number but you could always have them pass your number to him to call you should he wish

 

i talked to the mechanic today and he said it would be alot of work because it has an aftermarket transmission in it and he dosent know what gears are in it

 

Are you positive it's the gears? Can you pop the factory wheels on and then check the speedo?

Sounds like a lot of trouble. Lot easier than digging into your tranny.. Btw who installs an entire aftermarket tranny? The mechanic Sounds a little wavy...

 

Its not going to be the tires that are throwing your speedo off. These cars will calibrate themselves for tires size. I had 15s stock on mine, went to 17s with no change. Even had it calibrated, for an unrelated reason, and it showed that.

More then likely, if its off that much, the previos owner had gears installed and that threw it off. There are ways to check the ratio without have to rip anything out, but you do need to remove the dif cover.

 

What?! Wheel and tire size does matter, you must keep the same diameter.

 

Diameter is the key regardless of wheel and tyre combinations

 

How can you say regardless of wheel and tire combination, when those two things make up the diameter? Huh

 

I have a Diablosport Predator tuner. Well worth the investment. You can also check the gear ratio comparing revolutions of a drive wheel with the driveshaft.

 

Like I said: diameter is the key!

 

Respectfully. Nope.
I swapped the stock 17s for 18s on the 01 GT and it instantly threw the speedo off...considerably at that. It took the Predator to dial in a code to compensate. My 00 has had more wheels than I've had shoes. Each time, I had to break out the hand held tuner.