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Motive Gear Performance Plus Ring and Pinion Gear Kit; 3.90 Gear Ratio (10-14 GT, BOSS 302, GT500)

Item 21102G11
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      Product Information

      Features, Description, Reviews, Specs & Installation


      • Superior Quality
      • CNC-Cut from 8620 Gear Steel
      • 3.90 Gear Ratio
      • 8.8" Ring Gear Diameter
      • For Street or Track Use
      • Fits 2010-2014 GT, BOSS and GT500 Mustangs


      Improve Overall Performance. A set of Motive Performance gears will wake up your Pony and get it moving faster off the line. Steeper gears are a great way to lower quarter mile times and improve responsiveness without sacrificing drivability. 3.90 gears are perfect for the Pony that needs more than 3.73s but less than 4.10s, offering a great blend of performance and efficiency.

      Superior Construction & Precision Fit. These Motive ring and pinion gears are CNC cut from high grade 8620 gear steel and factory lapped for precision fit. Each set is hardness tested prior to leaving the factory to ensure the highest quality. Unlike other brands, Motive Gears do not have a reputation for "gear whine."

      Application. This Motive Performance Plus 3.90 Ring and Pinion Gear set will fit 2010-2014 GT, Boss and GT500 Mustangs. A master bearing kit is recommended by most installers, especially on high mileage vehicles, see drop down option above.

      Attention 2010 and newer Mustang Owners. Starting in 2010, Ford changed the inner rear gear pinion bearing in all 8.8" equipped Mustangs. Due to this, installation will require a new 8.8" rear gear pinion bearing (Ford part# 9L3Z-4630-A) for proper installation, please see drop down option above.

      Technical Note. Installation costs will vary, but a good rule of thumb is between $250 and $300. Be sure to work with a reliable shop that you trust for installations. You can also save money on your installation labor by having your Trac-Lok rebuilt at the same time as your gears are installed, see drop down option above.

      Fitment: 2010 2011 2012 2013 2014 Details

      MPN# F888390

      CA Residents: WARNING: Cancer and Reproductive Harm -


      Customer Reviews (10)

      Write a Review

      Ratings Summary

      4.4 out of 5 overall rating from 10 customers

      Installation Time: Weekend

      Installation Cost: $100-$250

      • November 30, 2018

        5 2012 GT - Lexus Installation Time: Shop Install Installation Cost: $250-$500

        Daily driven race car

        I daily drive my 2012 track pack (3.73 stock). Along with the carbon disc traction lok differential and these gears car feels brand new. I added a lightweight fly wheel and ACT clutch an now I’m pulling a car and a half and on my buddies FBO cobra jet set up. I’m FBO with a boss manifold. Compared to being behind a half car before. Until your getting on it it’s drives very similar to 3.73 if your worried about highway or shifting to often.

        Helpful (2)
      • December 18, 2017

        5 2012 GT - Robert Installation Time: Shop Install Installation Cost: $100-$250

        Great product!

        Great looking parts and they did the job! Still doing a 500 mile break in on the new set of gears, so I can't really test the performance gain.

        Helpful (3)
      • January 19, 2016

        4 2014 GT - Clean14 Installation Time: Afternoon

        Get up and go!

        It's true what they say about the whine. It's more like a humming. I usually don't hear it due to cat deletes and American Thunder axle backs. I wanted to put the friction modifier in but was assured the Royal Purple already contained it. On the plus side, it really gets up and leaves! I can smoke tires in 3rd gear now! I didn't want to go 4:10. That would've been too much. These 3:90's are perfect. A little more $$ than the FRPP 4:10's, but worth it. I still get a little over 19 mpg hwy. Got that! What's next?!

        Helpful (4)
      • October 10, 2013

        4 2013 Boss - DMCAP Installation Time: Full Day

        3:90 GEARS

        Brought it up about 200 rpm's at 60. Gave the car alittle more pickup without killing fuel milege

        Helpful (4)
      • June 08, 2013

        5 2012 GT - Steve66 Installation Time: Full Day

        Great gear!

        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.

        Helpful (6)
      • July 14, 2010

        3 - Matt


        Had gear professionally installed, greater acceleration and higher rpms, unfortunately the gear whines, would recommend ford racing, but they dont make a 390 so i chose motive because i wanted a 390, ill live w it

        Helpful (3)
      • June 02, 2010

        5 - chalmers

        perfect gear

        great gear not to low like 410s but still feels better then 373s.. i had gotten a rebuild kit with the gears.. i have not had any whine unless in reverse..

        Helpful (4)
      • December 05, 2009

        3 - david


        good compromise from 4.10s but have a tendency to whine.

        Helpful (4)
      • September 10, 2009

        5 - Brian

        better than 4.10s imo

        Went from stock to 4.10s. that lasted about a year. Decided to go down to 3.90s. They are definatly a much more street friendly gear, but still get up and move! 3rd redlines at about 85, and 4th is around 115, so you'll definatly still have plenty of oomph to blow past the slow traffic on the freeway-

        Helpful (5)
      • October 09, 2007

        5 - Travis

        Great get up and go.

        I feel that these are the great in between gears to have. I didn\'t want 3.73\\\'s but I didn\'t want 4.10\\\'s either. You will get a great improvement when you hit the throttle.

        Helpful (8)

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      Installation & What's in the Box

      Installation Info

      What's in the Box

      • (1) Ring gear
      • (1) Pinion gear

      Tech Specs

      Approximate RPM for 2011+ GT

      Gear @25 MPH @35 MPH @45 MPH @55 MPH @65 MPH @75 MPH
      1 4402 6163        
      2 2923 4092 5261 6430    
      3 2033 2846 3659 4472 5285 6098
      4 1588 2223 2858 3493 4128 4763
      5 1203 1684 2165 2646 3127 3608
      6 782 1094 1407 1720 2033 2345

      Gear @25 MPH @35 MPH @45 MPH @55 MPH @65 MPH @75 MPH
      1 5016          
      2 2814 3940 5066 6191    
      3 1829 2561 3293 4024 4756 5488
      4 1375 1925 2474 3024 3574 4124
      5 1043 1460 1877 2294 2711 3128
      6 831 1163 1496 1828 2161 2493

      Will It Fit My Mustang

      • Boss 302 - 12, 13
      • GT - 10, 11, 12, 13, 14
      • GT500 - 10, 11, 12, 13, 14

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