The Crane Axle 40 Spline Rear Spindle Kit is designed for high-load rear axle applications where factory spindle systems are no longer sufficient. Engineered for rock racing, competition crawlers, heavy trail rigs, and custom fabricated axle housings, these spindles are machined from 4140 chromoly steel and built to support massive 40 spline axle shafts under extreme torque and suspension load conditions.

Each spindle is machined in-house, heat treated for improved hardness, and finish-ground for precise wheel bearing fitment. Compared to traditional factory spindle systems, the increased spindle wall thickness and larger shaft capacity dramatically improve resistance to bending and twisting under load. The spindle design also supports a wide range of custom fabrication needs, allowing the spindle end to be machined down for compatibility with smaller axle tube bores while retaining the strength advantages of a 40 spline wheel end system.

Includes:

• (2) 4140 Chromoly 14-Bolt 40 Spline Spindles
• (4) 40 Spline Spindle Nuts
• (2) Spindle Nut Retaining Dowels

Optional:

• Crane 40 Spline Spindle Socket sold separately

Specifications

• Designed for 40 spline rear axle assemblies
• Machined from 4140 chromoly steel
• Heat treated for increased hardness and durability
• Precision finish-ground bearing surfaces
• Standard 3.00" outer diameter spindle body
• Can be machined to fit axle tube bores as small as 2.00"
• Heavy-duty extended weld surface design
• Intended for custom fabricated axle housings
• Made in the USA

Fitment

Fitment Notes:

• Designed for custom fabricated rear axle applications
• Requires modification of wheel hubs internally
• Compatible with 40 spline axle shaft systems
• Spindle O.D. may be machined for smaller axle tube bore sizes
• Intended for fabricated and high-strength rear axle builds

Tech Insight

Large tires, high horsepower, and aggressive off-road traction place substantial stress on rear spindle systems, especially in competition environments where shock loads are repeated continuously. Factory spindle systems can become a failure point due to limited spindle wall thickness and smaller axle shaft capacity.

By increasing spindle wall thickness and supporting 40 spline axle shafts, this system significantly improves resistance to spindle flex and torsional load. The extended weld surface also improves spindle-to-housing strength in fabricated axle applications. Because the spindle body can be machined for smaller bore housings, builders gain additional flexibility when designing custom rear axle assemblies without giving up the benefits of a heavy-duty 40 spline wheel end.