If it reads 15mph slow at all speeds. It's not the speedometer gear. The needle is not indexed properly. If it's the speedometer gear the error would be small at low numbers. Like 0 would be 0 regardless of the incorrect gear. Then for example 1 mph out at 10 mph and 5 at 50 and 10 at 100, that's an incorrect gear.

 

Yeah when it says I am going 80 I am only going like 65 on the highway,how would the speedometer needle be wrong?

 

So it's 15mph fast. What does it read when your going slower than that, like around 30?

 

ok, nobody has asked the magical question... is it auto or stick

also, I doubt your speedo is indexed wrong... only stupid people come up with **** like that!

If you have a stick, the trans needs to be dropped and the tailshaft housing removed. swap the speedo drive gear on the output shaft, and swap the driven gear on the sensor

If its auto, you cannot do a gear swap to get it correct...


Normally, you would be SOL if you didnt want to/werent able to do the above.... HOWEVER, since your speedo is electronic, you can use the Speedcal! get the proper speedo gear for what your car had stock, install and set the speedcal and be done with it

 

you have to drop the tranny to remove the tailshaft?

 

no, but not everyone is as good am I am!

besides... even though I had mine out of the car, it was still a ***** to get the housing back on...

never quite figured out why

 

on my m5r2 its cake

 

Yeah it's a 5 speed who would have an automatic mustang gt? Hahaha