Disclosed are modular mechanical assemblies formed from durable, corrosion resistant components with sufficient strength to maintain efficient operation. The modular mechanical assemblies include a novel torsion axle assembly having a cartridge that houses a torsion bar with a splined tip. A load bearing, relatively incompressible bushing is optionally disposed about the torsion bar. The cartridge is inserted into an axle tube, and an end cap is placed over the cartridge and torsion bar. The end cap is affixed to the axle tube such that the bushing is secured within a bore in the end cap. The torsion bar tip extends through the bushing and end cap and is secured within a torsion arm. A spindle is also secured within the torsion arm. One or more components of the torsion axle assembly are made from a low alloy, medium carbon steel material that provides corrosion resistance and advantageous yield and ultimate strength properties. One or more components of the assembly can also be coated to improve corrosion resistance. Suitable coating techniques include, but are not limited to liquid ferritic nitrocarburizing, gas nitriding, electroless nickel plating, or a diamond like carbon coating process.