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Motive Gear Performance Plus Ring and Pinion Gear Kit - 3.90 Gear Ratio (99-04 GT)

Item 21102G99
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      Product Information

      Features, Description, Reviews, Q&A, 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 1999-2004 GT, Bullitt, Mach 1 and Cobra 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 driveability. 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 pinon 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".

      Recommended Upgrade. Changing the rear axle gear ratio will throw off the calibration of your Mustangs speedometer, but a Ford Racing Speedometer Recalibration Tool is an inexpensive way to fix this issue.

      Application. This Motive Performance Plus 3.90 Ring and Pinion Gear set will fit all 1999 to 2004 V8 Mustangs including the GT, Bullitt, Mach 1 and Cobra models. A master bearing kit is recommended by most installers, especially on high mileage vehicles, 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: 1999 2000 2001 2002 2003 2004 Details

      MPN# F888390

      CA Residents: WARNING: Cancer and Reproductive Harm -


      Customer Reviews (18)

      Write a Review

      Ratings Summary

      4.6 out of 5 overall rating from 18 customers

      Installation Time: Weekend

      Installation Cost: $250-$500

      • November 13, 2018

        4 2001 GT - MatthewG


        These gears are top quality. I heard ford performance gears were the only ones that didn’t whine, but I wanted just a bit more than the 3.73 they offered. These gears do have a bit of whine especially at cruising throttle in 4th but really not that bad. Car does pull a noticeable amount harder, definitely like the 3.90

        Helpful (3)
      • February 20, 2018

        5 2001 Cobra - Tarako

        Spicey Talako

        I received my items in a timely manner, and I am just waiting to find a quality shop to install my gears, so I can go and have some fun.

        Helpful (5)
      • November 18, 2017

        5 2003 Cobra - stvenkng Installation Time: Weekend


        This is the gear that every street driven Cobra needs, it has awakened my 03 Vert like nothing else I have done and still keeps it in a decent range when driving at speed on the Interstate... It has drastically improved launch and E.T. and just makes the car feel totally different. The Motive Gear set has proven to be strong enough to hold anything I have thrown at it with nearly 700 rear wheel HP and 600 plus torque.. I installed the gear set and a new clutch and pressure plate by myself over a weekend but don't recommend anyone with less than an extensive knowledge of the Terminator and advanced mechanical skills attempt this on your own. I do recommend anyone looking at a 3.73 gear give the 3.90 a look...

        Helpful (5)
      • November 11, 2017

        5 2003 V6 - AnthonyH Installation Time: Full Day

        great gears!

        Did an 8.8 swap in my v6 about 2years ago and decided i wanted to have some more get up and go. Rebuilt the entire differential, swapped the gears, rebuilt the clutch. These gears are great! Put 500 miles on them to break them in, and my car gets up a lot faster now. No gear whine or noise. Perfect for anyone who wants a little more than 3.73 but not as much as the 4.10

        Helpful (5)
      • June 19, 2017

        5 2004 GT - Steevo Installation Time: Shop Install Installation Cost: $500-$1000

        Gear set

        Looks to be a real nice set of rear gears if and when i get them installed,waiting on a part to arrive still. These are going to be the best of both worlds if you want a little quicker acceleration and mire power in every gear. 4.10 and up are more for just drag racing, these with give you good top speed and good pick up. Its costing me 750$ to have them installed but its by a pro who is also putting in everything new,axles,diff,bearings,seals,everything.

        Helpful (7)
      • April 20, 2017

        5 2004 GT - CrowdHunter Installation Time: Afternoon

        Good upgrade with track proven results

        Before I installed these gears my 2004 GT auto was running consistant 14.0s with the occasional 13.90s pass with 99mph trap speed. My personal best was a 13.90 at 99mph with street tires and a 13.98 at 99mph with the MT ET drag radials (they are pretty heavy tire, 275/50/15). I installed thesse with the Ford Racing rebuild kit and was able to run a best of a 13.77 at 100mph with bald Mickey Thompson ET's. I'm hoping to get a few hundredths off with the fresh MT DRs that I have and will be moving to the Hoosier QTP radial as they are about 14lbs lighter each then the MTs. Hoping that loss of rotational weight will get me around a tenth off and crack into the 13.60s. Driving wise, this is my daily. With the stock 3.27s I was getting about 250-ish miles per tank. With the 3.90s I am now getting around 230-ish miles per tank. Went from about 22mpg to 20 mpg-ish. These do have a bit of a howl to them and I experience it mostly when daily driving from the 45-55 mph range while excelerating. I do not notice any noise while at the drag strip. Decel while daily driving or racing I notice no noise. Freeway speed of 75mph is about 2550 rpm. I did have these professionally installed for $300 and it took the shop about 3 hours. I definitely suggest thse to anyone that is looking for a decent street/strip gear that is not afraid of the chance of a little howl.

        Helpful (7)
      • February 23, 2017

        5 2004 GT - TerenceB

        3.90 motive gear

        Great performance, not bad on gas mileage, good price.

        Helpful (6)
      • September 25, 2016

        5 2000 GT - BobusGuy


        Like a whole new car! The break in period darn near killed me. Thought about pulling a Ferris Bueller haha

        Helpful (7)
      • May 01, 2016

        4 1999 Cobra - pennywel Installation Time: Shop Install Installation Cost: $100-$250

        Turn-up the stereo, then punch it!

        When I removed the IRS subframe last year, I took the Diff to Ronnie at Prime Time Racing on Summit Av in Greensboro, NC. He installed the Motive 3.90 gear for $250. With poly subframe bushings, Delrin upper / lower control arm bushings, aluminum Diff bushings front and rear and a number of other suspension goodies, I re-installed the IRS. I followed Ronnie's break-in procedure: cycle the rearend from hot to cool four times. I ran the car for 4 miles at 3K plus rpm, then 3 miles at less than 1500 rpm. I do have gear noise, but it is not what I call a "whine." It sounds like new sheet metal sliding back and forth at a medium to low frequency. SHMotorsports warns for this reason to use only Ford Racing gears. But like so many others have commented, 3.73 is not enough and 4.10 is a royal pain. This gear pulls like a supersonic freight train. As such, I normally start in 2ND gear without slipping the clutch and you can accelerate in 5th with some authority, but it is much more fun to grab a lower gear. My gas mileage dropped from 24/25 mpg to 21 mpg on the highway. I recommend this gear for highway and autocross, but not for daily driving because of the cost of fuel. I wish Ford Racing made the same ratio so Motive would not feel compelled to stick us with the high price.

        Helpful (7)
      • July 14, 2013

        5 1999 Cobra - Niixx Installation Time: Shop Install Installation Cost: $250-$500

        Woke up my 4.6 more than any other upgrade

        This was a great investment. Went from stock 3.27's to these. My 99 cobra has never had so much useable power. I hit about 2700 rpm at 75mph with a T-45 tranny in 5th so it's still completely highway capable. This also helped minimize the cam lope I had while in gear at lower rpms. I will be needing new tires now though. Over all a great buy. One note is the shop I used didn't have the right size shims so it took a few days for install. Also u will need to adjust your tune to the new ratio or your speed-O will be off by quite a bit.

        Helpful (6)

      Questions & Answers (3 answers)

      3 Top Rated Questions

      Fitment says will not fit my 01 Cobra. But down in the description or below it says fits all 8.8 of ear ends. Is there something different about my cobra 8.8 that I dont know about? And why does your descriptions contradict one another?

      • We apologize for the confusion, this gear kit will work with your 2001 Cobra Mustang and you will not have an issue getting this installed. We will be updating our site as well to reflect this as well.

      Helpful (0)

      Are these gears good for a daily driver? I drive 25 miles to work at 70-80 mph

      • The Motive Performance Plus 3.90 Gears can be used for a car that is daily driven, the rpm range for that speed will increase because of the gear size, but it can be used without issue.

      Helpful (0)

      What kind of oil is recommended for these gears?

      • The type of oil that is recommended for these gears will vary. If you street, daily drive, or live in a warmer climate you will want to purchase 75w90. If you live in a colder climate or drag race your Mustang, you will want to use 75w140.

      Helpful (0)
      Post Your Question

      Installation & What's in the Box

      Installation Info

      What's in the Box

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

      Tech Specs

      Approximate RPM for 1999-2004 GT

      Gear @25 MPH @35 MPH @45 MPH @55 MPH @65 MPH @75 MPH
      1 4065 5691        
      2 2405 3368 4330 5292 6254  
      3 1588 2223 2858 3493 4128 4763
      4 1203 1684 2165 2646 3127 3608
      5 818 1145 1472 1799 2126 2453

      Gear @25 MPH @35 MPH @45 MPH @55 MPH @65 MPH @75 MPH
      1 3416 4782 6148      
      2 1864 2610 3355 4101 4847 5592
      3 1203 1684 2165 2646 3127 3608
      4 842 1179 1515 1852 2189 2526

      Will It Fit My Mustang

      • Bullitt - 01
      • GT - 99, 00, 01, 02, 03, 04

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