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EXCEL from Richmond Ring Gear and Pinion Kit - 3.90 Gears (86-93 GT)

Market Price $186.39 You Save 12% ($21.44)
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  • Item 21527G87

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    Features & Details

    • Superior Quality
    • 3.90:1 Gear Ratio
    • 8.8" Ring Gear Diameter
    • For Street or Track Use
    • Made in the USA
    • Fits 1986-1993 GT, 5.0 LX and SVT Cobra
    Improve Off The Line Acceleration. Has your 5.0L Mustang always felt a little sluggish from a standing start? If so, it is probably because of the lower ratio gear and pinion installed by Ford at the factory. Most 5.0L Mustangs came equipped with 3.08 or 3.27 gears, which are fine for daily drivers who are looking for good fuel economy, but not for the hardcore performance enthusiast. By installing a set of higher ratio 3.90 gears your Mustang will enter its power band quicker which will improve low end torque for faster off the line acceleration.

    Superior Quality. Richmond proudly manufactures their Ring and Pinion Gear Sets right here in the USA. Using state-of-the-art manufacturing processes and extensive quality control testing, Richmond produces a superior quality Ring and Pinion Gear Set at an excellent price. Richmond is so confident in the quality of their products that they back them with a 6 month, 50,000 mile no-nonsense warranty. 

    Recommended Upgrade. Please note that when changing the gear ratio of your Mustangs rear differential that the calibration of your speedometer will no longer be correct and will display the wrong speed. However, you can easily fix this annoying issue with a new Speedometer Gear (sold separately).

    Application. This 3.90 ratio Richmond Excel Ring and Pinion Gear set will fit all 1986 to 1993 V8 Mustangs equipped with an 8.8" solid axle rear end, including the GT, 5.0 LX, and SVT 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: 1986 1987 1988 1989 1990 1991 1992 1993 Details

    MPN# F88389

    CA Residents: WARNING: Cancer and Reproductive Harm -

    What's in the Box
    • (1) Ring gear
    • (1) Pinion gear
    Installation Info
    Tech Specs

    Approximate RPM for 1986-1993 GT

    Gear @25 MPH @35 MPH @45 MPH @55 MPH @65 MPH @75 MPH
    1 4053 5674        
    2 2393 3351 4308 5265 6223  
    3 1600 2239 2879 3519 4159 4799
    4 1203 1684 2165 2646 3127 3608
    5 806 1128 1450 1773 2095 2417

    Gear @25 MPH @35 MPH @45 MPH @55 MPH @65 MPH @75 MPH
    1 2886 4041 5196 6350    
    2 1764 2470 3175 3881 4586 5292
    3 1203 1684 2165 2646 3127 3608
    4 802 1123 1443 1764 2085 2405
    Will it fit my Mustang?

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    Customer Reviews (3) Write a Review

    Overall Rating 3

    out of 5 stars

    Installation Time:Weekend

    • Performance Gain 4 4
    • Fit 5 5

    • 5/5

      Installation Time: Weekend

      August 07, 2017


      I ordered these 3.90's with the installation kit and did it all myself for the first time...instructions make it super easy! Not noisy like everyone says! Don't forget to set your pinion preload or they'll be noisy on deceleration.


      Year: 1990 Submodel: GT

      Helpful (3)

    • 3/5

      October 14, 2010

      Richmond Gears 3.90

      The 3.90 gears really improve your acceleration and are the cheapest way to go faster without sacrificing too much fuel mileage/drivability. I was impressed by the quickness in which my order was received to my front door. However, after installing my 3.90 gears (making sure that both the pinion depth and backlash were correct) I noticed a whine. The whine did not subside after the break in period. I contacted AM who was very helpful and was instructed to speak with Richmond. Richmond did not really do anything to help me and hopefully the gears hold up. So far noise is the only problem. If I could do it again I would purchase Ford Racing gears.

      Bill Henry

      Helpful (5)

    • 1/5

      January 09, 2010


      Good ratio...VERY NOISY at cruise...and yes it is set up right ..pattern was perfect......replacing with FORD Gears....also Motive Kit for 8.8 did not include any small shims....only 14's and 30's.

      chris s

      Helpful (4)

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