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Traxxas Gearbox Halves, Shift Detent B (Traxxas 3991X | TRA3991X)

Model: Traxxas 3991X
Dist. #: TRA3991X   SKU: TRA3991X

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Shipping: In Stock For Shipping
Store Pickup:

South Jordan, UT
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Price:  $10.49

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Updated on Apr 23, 2026 11:52:08 PM

Gearbox Halves Front/Rear E-Maxx...
These are the replacement Gearbox Halves for the Traxxas E-Maxx Truck.

FEATURES:
Black plastic building

INCLUDES:
Gearbox halves (front and rear) and screws

REQUIRES:
Rest of the gearbox contents

SPECS:
Length: 2.67 (68mm) (at best point)
Width: 3.42" (87mm) (at best point)

Here is a fantastic item that several others have bought at the same time.

Output Shaft, Transmission

This is the Transmission Output Shaft for the Traxxas E-Maxx.

FEATURES:
Metal building, black in color

INCLUDES:
One transmission output shaft, Part #5369

REQUIRES:
Setup on the Traxxas E-Maxx

SPECS:
Overall length: 2.75" (70mm)
Size of drive pet dog mount: .39" (10mm)
Size of shaft: .23" (6mm)

This item compliments the above talked about item.

Output Gear, 33 T W/ Spacers (

This is the Output Gear 33T for the Traxxas E-Maxx Truck.

FEATURES:
Black nylon building

INCLUDES:
One 33T output gear
Two spacers

REQUIRES:
Silicone Grease, usage TRAC6037

SPECS:
Outer diameter: 1.37" (35mm)
Density: 1.02" (26mm)

This item compliments the main item below.

Input Shaft/ Drive Gear Assemb

This is the replacement Input Shaft/Drive Gear Assembly for the
Traxxas 3905 E-Maxx Truck.

FEATURES:
Steel shaft, black in color
Steel drive gear assembly, silver in color

INCLUDES:
One Input Shaft with 18 Tooth Top Gear

REQUIRES:
Setup following the design handbook

SPECS:
Shaft Size: 5mm
Shaft Length: 3.53" (90mm)
Thread Size: 4mm

This item compliments the main item below.

Idler Gear, 20-Tooth/ Idler Ge

This is the replacement 20 Tooth Idler Gear and Shaft for the
Traxxas E-Maxx 4WD RTR.

FEATURES:
Steel building, weapon metal in color
Changes a used or broken idler gear and shaft

INCLUDES:
One 20 Tooth Idler Gear
One 5x18mm Idler Gear Shaft

REQUIRES:
Setup following the design handbook

SPECS:
Externally Size: .86" (22mm)
Inside Size: .43" (11mm)
Density: .50" (12.5mm)

This item compliments the above talked about item.

5 X 11 X 4Mm Ball Bearing (2) Blue Rubber Shield R Evo

This is a 2 pack of 5X11mm Ball Bearings for the Traxxas Revo.

FEATURES:
Metal bearing building
Blue rubber dirt shields

INCLUDES:
(2) 5X11mm ball bearings, Part #5116

SPECS:
Inside diameter: 3/16" (5mm)
Externally diameter: 7/16" (11mm)
Width: 5/32" (4mm)

The listed below item also pairs really well with the item being talked about.

6 X 12 X 4Mm Ball Bearing (2) Blue Rubber Sheild R Evo

This is a 6X12mm Ball Bearing Set from Traxxas.

FEATURES:
Steel building
Blue rubber dirt shields

INCLUDES:
(2) ball bearings, Part #5117

SPECS:
Inside diameter: 6mm
Externally diameter: 12mm
Width: 4mm

COMMENTS:
This bearing set is utilized in the transmission and differentials of
    the Revo.

This is a superb enhancement to the item currently being talked about.

Motor Plate For Single Motor

This is the optional Single Motor Plate for the
Traxxas E-Maxx 16.8V RTR.

FEATURES:
Aluminum building, blue in color
Created for a clean install of a single brushless motor system in
the E-Maxx 16.8V RTR (needs gear cover number TRAC3997)

INCLUDES:
One Aluminum Motor Plate

REQUIRES:
Setup and motor cover number TRAC3997
X-Plosion Parts Finder Part also Fits on the vehicles below:

Frequently Bought Together

Traxxas Gearbox Halves, Shift Detent B
+
Traxxas Idler Gear, 20-Tooth/ Idler Ge
+
Traxxas Output Shaft, Transmission
This Item: Traxxas Gearbox Halves, Shift Detent B
$10.49
Traxxas Idler Gear, 20-Tooth/ Idler Ge
$5.99
Traxxas Output Shaft, Transmission
$7.99

Total Price: $24.47

Add All Three To Cart

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