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GrudgeBox Builder's Kit

Built to take high horsepower abuse found in late model H-D performance applications while providing elegant shift precision.

Transmission Configurations

  • GrudgeBox - Straight 1st, 2nd 3rd, 4th, 5th and 6th gears, design and geared for performance buffs, racers and speed freaks seeking negligible power loss.


  • 2006-later Dyna
  • 2007-later Softail & Touring


    • All gears are straight cut for negligible parasitic power loss, providing maximum power transfer to the rear wheel
    • Wide-ratio gearing for heavier performance applications
    • Built for aggressive take-offs and long distances at above-average speeds
    • 250 RPM drop at higher highway speeds (approx. 80 mph)
    • Engineering focus on excessive durability
    • Bulletproof main drive gear bearing (patent pending)
    • Gears up to 40% wider than stock
    • Positive dog tooth engagement in gear with pie-shaped shift dogs
    • Frictionless linear detent shift system for smooth shifting
    • Redundant neutral detent to make it easy to find neutral
    • Low effort, single-axis/linear motion ratchet pawl for crisp, tight and easy shifting
    • More durable than stock
    • No case modifications required for installation

    GrudgeBox Installation Instructions for 3.15 1st gear


    • 4° Back Cut Shift Dogs
      More hook for the hold! The 4° back cut angle on all GrudgeBox shift dogs ensures positive gear engagement and eliminates hop out.
    • Shift System
      Shift with certainty! The GrudgeBox features our frictionless linear detent shift system. The shift drum utilizes a fixed spindle design for smooth, low inertia, indexing. It’s easy to find neutral with our redundant neutral detent, which is incorporated into the architecture of the shift system.
      • A) Smooth linear 11/32” detent ball bearing riding on 60 micro ball bearings
      • B) Linear motion is controlled by a caged 24 micro ball bearing assembly
      • C) 44lb/in compression spring
    • New Pawl Design
      Shift with ease! Conventional shifter pawls have a 2-point pivot system. Our new low effort single-axis/linear motion shifter pawl rotates from one central pivot point, allowing continuous motion throughout the shift. Overshift inhibitors prevent any
      missed shifts.
    • Speedometer Reluctor Ring
      Stay calibrated! The GrudgeBox utilizes a speedometer reluctor ring for sending the vehicle speed signal through the stock speed sensor, keeping the pulses per mile the same as stock. Your speedometer will indicate the correct speed without the use of a recalibration box. PCM reflash is required for correct gear indication and proper cruise control operation.
    • DynoJet Power Vision calibration numbers:
    • Bigger Gears
      Stronger! The GrudgeBox gears are up to 40% wider than stock for superior strength and durability.
    • Pie Shaped Shift Dogs
      Positive shift engagement! Intended for high horsepower applications and well suited for everyday cruising, the pie-shaped shift dogs used in the GrudgeBox provide significantly more dog tooth/pocket landing area for positive dog tooth engagement while in gear.
    • Main Drive Gear Bearing 
      Bulletproof! The GrudgeBox comes with our exclusive double tapered roller bearing assembly (patent pending) to eliminate the all too common stock main drive gear bearing failures.
    • Simpler Pawl Design
      Built for a beating! Conventional shifter pawls have a 2-point pivot system. Our new single-axis/linear motion shifter pawl has fewer points of motion and will hold up under high horsepower and aggressive shifting.


    • New Generation OVERDRIVE
      Cruise at 80 mph with the overdrive 6th gear, lowering RPM on the highway for improved fuel economy, reduced vibration and less wear and tear on the rider.
    • .92 overdrive in 6th gear provides a 250 rpm reduction while cruising at 80 mph.

    Transmission Ratios 


    Stock H-D














    New PN

    Old PN





    GrudgeBox, 3.15 1st gear ratio

    2006-Later Dyna, 2007-Later Softail/Touring

    GB6-M8 GBSTR17 GrudgeBox, 3.15 1st gear ratio 2017 Milwaukee 8 models


    Engineered and manufactured in the USA with a focus on excessive torque capacity and crisp shifting. Included is our 5-year/50,000 mile limited warranty for worry-free, aggressive riding.


    Standard Gear Case Finish Examples (Not applicable to all products)




    Wrinkle Black

    These example finishes are intended to show the exterior treatments of cases, top covers and doors.

    TERM AND CONDITIONS                                                                                         

    • BAKER Drivetrain reserves the right to change prices, terms or policies at any time without notice.
    • Orders can be pre-paid using Visa, MasterCard, American Express, Discover or PayPal.
    • All orders not pre-paid will be sent C.O.D. certified check or money order only unless pre-approved for company check acceptance.
    • Any orders from outside the USA must be pre-paid in US funds via wire transfer; a $30 transfer fee will apply.
    • Prices shown are F.O.B. Haslett, MI.


    BAKER™ transmission assemblies, transmission kits, primaries, and oil pans are guaranteed to the original purchaser to be free of manufacturing defects in materials and workmanship for a period of 5 years from the date of purchase or up to 50,000 miles. BAKER™ clutches, kicker cover kits, belt drives, F6F kit, reverse systems, covers and accessories are guaranteed to the original purchaser to be free of manufacturing defects in materials and workmanship for a period of 2 years from the date of purchase or up to 24,000 miles - whichever occurs first. If the product is found by BAKER™ to be defective, such products will, at the option of BAKER™, be replaced or repaired at cost to BAKER™. 

    In the event warranty service is required, the original purchaser must call or write BAKER™ immediately with a description of the problem. If it is deemed necessary for BAKER™ to make an evaluation to determine whether the transmission assembly or transmission kit or accessory is defective, the entire transmission assembly, whether originally purchased as an assembly or kit, must be properly packaged and returned prepaid to BAKER™ with a copy of the original invoice of purchase. If after an evaluation has been made by BAKER™ and a defect in materials and/or workmanship is found, BAKER™  will, at BAKER™  option, repair or replace the defective part of the assembly. 


    Due to the uniqueness, low price and assembly outside of typical production process of products indicated as Insider Special products, purchasing these Insider Special products include a warranty so to guarantee the original purchaser to be free of manufacturing defects in materials and workmanship for a period of 1 year from the date of purchase or up to 12,000 miles. We have provided extended options for you to purchase below. 


    Any merchandise returned for any reason (exchange, credit or modification) must be accompanied by a Return Goods Authorization (RGA) number or it will be refused. Call BAKER™ to obtain this number prior to returning goods for any reason. There is a 15% re-stocking fee for all returned items. BAKER™ is not liable for any shipping charges. 


    NOTE: Limited warranty does not cover labor or other costs or expenses incidental to the repair and or replacement of BAKER™ products.

    This warranty does not apply if one or more of the following situations is judged by BAKER™ to be relevant: BAKER™ OEM transmissions; (these are subject to the OEM manufactures warranty only), Improper installation, accident, modification (including but not limited to use of unauthorized parts, transmission oils or lubricants), racing, high performance application, mishandling, misapplication, neglect (including but not limited to improper maintenance), or improper repair. 

    BAKER™ shall not be liable for any consequential or incidental damages arising out of or in connection with a BAKER™ transmission assembly, transmission kit, component or part. Consequential damages shall include without limitation, loss of use, income or profit, or losses sustained as the result of injury (including death) to any person or loss of or damage to property.

    BAKER™ transmissions, transmission kits and accessories are designed exclusively for use in American V-Twin motorcycles. BAKER™ shall have no warranty or liability obligation if BAKER™ parts are used in any other application.

    If it is determined that a BAKER™ product has been disassembled during the warranty period for any reason, this limited warranty will no longer apply unless you were instructed to do so by a BAKER Drivetrain technician for diagnostic purposes.

    The words H-D®, Softail®, FXR®, Dyna®, FLT®, FLH®, Sportster®, and Buell® are registered trademarks and are for reference only.

    GrudgeBox Builder's Kit
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    Customer Reviews
    4.6 Based on 27 Reviews
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    Filter Reviews:
    Jeff L.
    United States United States
    • What model motorcycle do you ride? 2014 HD Ultra Limited
    Grudge box in 2014 ultra

    Definitely purchase again! Most power to the wheel delivery of any transmission readily available on the market. My overbuilt 103 engine is currently putting out 152hp & 168tq. I had rebuilt 2 HD trannys before pulling the trigger on Grudge Box. Why Did I Wait?? This is the 3rd installation I have done now and I have noticed that the shifter pawl needs to be manipulated as cartridge is inserted for easiest fit. Installation is a breeze and well worth the investment. Do not purchase if a low rpm rider. You will find you do most riding in 3rd gear. This transmission will not disappoint!!

    Jeffrey M.
    United States United States
    • What model motorcycle do you ride? 2007 Harley Road Glide
    Baker Grudge box

    Transmission is holding up great so far I really like it do a lot of thrashing on the throttle lot of popping on the clutch gassing hard great buy I recommend

    United States United States
    grudge box

    very nice american made product great sevice even after the sale linda was awsume

    Mike S.
    United States United States
    • What model motorcycle do you ride? 2019 cvo limited
    Grudge box

    2019 cvo limited with bad shift forks due to oil transfer when bike was new. Bike just out of warranty when would not shift to hi gear and very noisy going into other gears. Dealer was no help, kept insisting there was no oil transfer out of trans and into primary. There was. Went with the grudgebox because of good reviews and mainly to handle my upgraded motor with 140/140 power. Baker box working fine, have about 2000 miles now and change oil twice. Only concern is that it doesn’t shift as easily as my OD6 in my 1995 evo FLH. That bike is with S&S 113 and runs great! Shifts smooth, neutral easy to find, no klunk into first, just great all the way. I’m hoping my new gear box will be as nice as the old one! Great dealing with Baker, customer service outstanding.

    JASON F.
    United States United States
    • What model motorcycle do you ride? 2014 street glide special
    Let it rip

    Love the transmission!

    Web Product ID: 5546426819
    Baker Drivetrain Team Illustration