How are steering gearbox issues diagnosed?
Since most power steering issues will generate the same symptoms, it would be difficult to diagnose only one part, without understand the condition of the whole system. When symptoms emerge, the power steering fluid is inspected, and topped off, and the condition, and tension of the belt is noted. The system may need to be bled of air prior to diagnosis. Any leaks will become very obvious at that time, and mechanical failure of the power steering pump will be evident from noise, or a pressure gauge inserted into the power steering line. At that time, if no other issues are found, the steering rack or steering gearbox will be suspected of failure, if the symptoms dictate. Any dust boots and seals will be inspected for leaks. The rack and pinion gear set will be inspected for sounds typical of mechanical failure, and the input and output shafts will be examined for play. This systematic approach will lead a technician to a diagnosis in short order, and ensure they know the entire system inside and out.

How is a steering gearbox replaced?
Before beginning the replacement of the steering gearbox, the servicing technician will prepare for the job by noting component locations, and removing items needed to access the gearbox, allowing its removal. The vehicle is then drained of power steering fluid as the hoses are disconnected from the steering gearbox. The steering column is unbolted, and the pitman arm ball joint is removed from the center link. Once free from any electrical connectors, on modern vehicles, the steering gearbox is unbolted from the chassis, and removed. On some vehicles, the steering gearbox is removed from the vehicle while sliding apart from the steering column splined shaft. Replacement is the opposite order of operations, followed by standard fill and bleed procedures for power steering systems.
RepairPal Recommendations for steering gearbox issues