GMGear is an equation and knowledge based system that uses an iterative process to generate multiple possible solutions for a gear set design. It evaluates and recommends the best gear set to meet performance requirements, geometric constraints and manufacturing considerations. Performance requirements include input torque and speed, gear ratio, weight, noise and duty cycle life. Geometry constraints are the envelope into which the gear set must fit, as defined by axial length and vertical size. Manufacturing considerations include tolerances, types of materials and the use of existing cutters, carriers and mating gears. GMGear takes advantage of Object-Oriented technology for implementation of domain information, and uses a sophisticated back chaining mechanism to apply equations towards reaching design solutions. We represented all gear variables and equations, as well as all physical components, methodology components and design results as objects. We designed and implemented this system so that the domain experts are responsible for maintaining the domain knowledge.