speedo problems after putting a 3.90:1 diff in an ef falcon - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars

bivo7 · 05-28-2009, 02:35

hello can any one help me, i have an ef falcon which i have installed a 3.90:1 diff in replace of the standard 3.25:1. my speedo is now not correct. where can i buy a 3.90:1 speed sensor for a t5 gear box?

If i cant buy one any one know how to modify the old one or fool the ecu to get correct speed readings

Steve83 · 05-28-2009, 16:10

You don't change the sensor - just the plastic gear on it. There are many websites with gear calculators, so do some searching. This one is for CrownVics, but it might work for you:
Speedo Gear Selection

Also...
It took me a few seconds to figure out that you were talking about a modern car. Falcons haven't been made in the US for some time, so it would help if you add your car's specs to your signature &/or profile.