2006Arms forum
Finding and replacing arm trunnions for a 3A arm rebuild
20 years old. Gear and prices may have changed since.
What the thread found
- Arm trunnions can be replaced by machining fixed axis rods in place of the original trunnions if you have access to a lathe and machine shop equipment.
- Standard hardened steel axis rods approximately 3 inches in length can be used as replacements, connecting both sides of the arm for increased rigidity and reduced twisting under load.
- Metal caps need to be fabricated to retain the replacement axis rods in place of the original trunnions.
- Bearings in the arm can be sourced from local hardware stores using the type number printed on them, saving significant cost compared to specialty suppliers.
- Heating the aluminum arm allows old bearings to be pressed out and new ones installed with appropriate equipment.
- Trunnions and bearings can be replaced incrementally rather than all at once.
- Some manufacturers produce replacement trunnions, including stainless steel versions that extend fully through the arm structure for added support.
- The original 3A arm patents have expired, allowing multiple manufacturers to produce replacement arms and components.
Depends on
- This approach requires significant skill, proper tools, and access to machine shop equipment.
- Mistakes during bearing replacement or trunnion work can damage the aluminum arm structure.
- Not all manufacturers are willing to sell individual parts rather than complete rebuild services.
- The discussion includes manufacturer recommendations and contact information that may be outdated given the 2006 timeframe.