[Ridinlow6969]

now i know there are a lot of post about rear end gears but i could not find some answers i was looking for and hope that someone can help me out. Im looking to install a set of 3.73's in my 05 v6 mustang, its an auto by the way. And I was wondering if you have to tune the ecu with a after market programmer, or if the gears can be installed without a tune. I know i hear that it will mess with my speedometer but will it have any other bad affects? i read somewheres that a guy was having trouble with his transmission when in overdrive because he didnt tune the ecu for the new gears. The reason im asking this is because the dealers in my area are telling me that they will void my warranty if they see any sign of a programmers chip being used. if anyone has a set of aftermarket gears on without a ecu tune let me know how everything is going, thanx.

[TheUNZippee!]

You do not need a tune for new gears. But you do need to recalibrate the speedometer for the new gear ratio. This is usually done with a tuner. So if you are spending money on gears, spend another few hundred, and buy a tuner with custom tunes which will only add to your power, and then you will have the added advantage of being able to adjust your speedometer for the new gears.

And welcome to the forums.

[00vabchgt]

welcome aboard. i'm with Zip. if you're worried about Ford voiding your warranty, just get a handheld tuner. it saves the factory tune, so when you take it in to the dealer for anything, just reinstall the stock tune. that's what i did.

[Ridinlow6969]

now if i get the tuner and tune it for the gears, when i revert back to factory setting to bring it get serviced or for repair work will they be able to see that i had a tune on the computer and that i have aftermarket gears? And which tuner would be the best for me to get?