June 08, 2013
After much research, I decided to go with the Motive 3.90 gear. I felt that the 3.73 would not be steep enough and 4.10's would be too steep as I drive my Mustang on the highway from time to time. I am definitely glad I went with the 3.90. The gear made my 2012 GT more responsive and much more torquey than the factory 3.31's without giving up drivability. If you're looking for an easy mod to increase your Mustang's power, this is it. I read several reviews indicating noisy gears and gear whine. I can only tell you my gear is extremely quiet, except for a very slight and almost unnoticeable whine during deceleration. This is typical with a steeper aftermarket gear due to the backlash setting. My advice is if you have the gear professionally installed, use a reputable and experienced installer who will treat your Mustang like it's theirs. Also, purchase the gear install kit and your Mustang's recommended gear oil. My Mustang required 75w140. Don't forget to purchase a bottle of Ford Racing friction modifier. This can be added to the gear oil and will help to reduce gear whine and chatter. Finally, follow Motive's instructions and break in your gear. First, heat cycle the gear several times. Drive for ten or fifteen minutes to heat the gears then park the car and allow them to cool completely. I did this eight times. Also, don't drive the car over 50 mph and don't drive at a constant speed. This helps the gear establish a wear pattern. Furthermore, it is recommended to drive the car 500 miles and re-check the gear and change the gear oil and friction modifier. I did all of the aforementioned and I could not be any happier with the new gear. It sounds like a lot, but believe me, it is well worth it!
In ending, I can only say that American Muscle's service is always second to none. Ordering and delivery is always easy and fast and they always answer my questions. I highly recommend the 3.90 Motive gear. You won't be disappointed.