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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
    • 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 are 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.
    • 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.


    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 and transmission builder 's kits, 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, whichever occurs first. All other BAKER products 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, except for the following; Warranty does not cover clutch plate wear, throw out bearing failures or mainshaft breakage due to improper clutch nut installation.Electrical components carry a 30-day warranty; cosmetic finishes (chrome plating, hard anodizing, powder coating) are covered for 60 days. Certain promotional products may carry a shorter warranty as specified at the time of purchase. 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 purchase invoice. If after evaluation by BAKER a defect in materials and/or workmanship is found, BAKER will, at their option, repair or replace the defective part of the assembly.


    Returns are permitted within 90 days of the delivery date. 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.


    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 manufacturers 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.

    GrudgeBox Builder's Kit
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    Customer Reviews
    4.6 Based on 42 Reviews
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    United States United States
    • What model motorcycle do you ride? 2022 street glide st

    The best Sales and support

    Fantastic could not have been any better hard to say more.

    BAKER Drivetrain GrudgeBox Builder's Kit Review
    Corinna T.
    United States United States
    • What model motorcycle do you ride? 2022 FLHTCUTG


    purchased for a customer who travels ALOT and he LOVES this kit!

    ricky g.
    United States United States
    • What model motorcycle do you ride? FxlrS, fxr

    Irritated to say the least

    Product was advertised to have a upgraded timken tapered roller main drive gear bearing. Was never told the product that I would be receiving had a stock ball bearing main drive gear. When I had a main drive gear bearing failure in my stock transmission I decided to pay the almost $4,000 to upgrade but I got the exact same as I had before with my stock setup. There was no price break no disclosure no return of emails or phone calls customer service severely lacking. And I'm very unhappy to say the least will probably never buy from Baker again.

    Byron C.
    United States United States
    • What model motorcycle do you ride? 2007 street glide

    Awesome transmission

    This transmission shift so smooth and the gear spread with my 107 engine is perfect

    BAKER Drivetrain GrudgeBox Builder's Kit Review
    United States United States
    • What model motorcycle do you ride? road king


    Grudgebox builders kit is awesome

    Web Product ID: 5546426819
    Baker Drivetrain Team Illustration