TH400 upgrade now speedo is way off!!!

[berrelauto]

We have a 2005 GTO in the shop and have converted it to a TH400
It had a T-56 in it from the factory

We install the correct reluctor wheel and speedo sensor in the car but it still is waaaaaaaaaaaaaay off...Its over 10 MPH off and we have no idea what to do to correct it

This car didnt have a TCM as its an 6sp car...We are thinking in might need a Auto engine tune and a auto dash to correct this issue but again we are not sure...

Any help would be great

[johnv]

go into speedo calibrations table H0101 and either add or subtract a % untill it reads correctly. Read the table discription to determin which way to go.

[Tre-Cool]

did you change H0102 from 17 to 40?

this would definetly cause your speedo to be out.

Just use the calculator but make sure you put 40teeth for the pickup