What is a steering gearbox?
The steering gearbox is the older and more heavy duty type of steering gear, and may be power steering, or manual steering. When the steering wheel is turned, the steering gear, whether power assisted or not, turns the pitman arm, which causes the wheels to turn.
How does the steering gearbox work?
The steering wheel is connected to the steering gear by the steering column. When the steering wheel is turned, the steering gear will turn the pitman arm, the link between the center link and the steering gear. The pitman arm and idler arm, which connects the other side of the center link to the chassis, hold the steering linkage up, and allow it to move to either side with the pitman arm. When the steering linkage moves to one side, the wheels turn in that direction, causing the vehicle to turn.
When a steering gearbox is failing, the steering effort may increase or become jerky and uneven. The steering linkage may feel loose, have excessive play, and the gearbox may leak fluid from the steering shaft shaft seals or cracks in the steering gearbox itself.
What are the symptoms related to a bad steering gearbox?
Power steering gearbox leaks and mechanical issues are evident as soon as the vehicle is moved, and power steering fluid on the ground is accompanied by strange noises and a different steering feel. Besides leaking oil, the power steering pump might being sounding overworked when turning normally as the steering gearbox begins to increase required input pressure before turning the wheels. Lastly, the steering gear may make a clunking noise, and the steering wheel would feel loose. When the mounting bolts break, or stretch, the steering gear will be permitted to move back and forth, which will also create noticeable wear marks on the mounting area.
Can I drive with a steering gearbox problem?
Power steering component failure almost always means a leak, but the amount of leaking fluid will determine if the vehicle can be driven. Also, if failure of the pulley or accessory belt occurs, the vehicle may be stranded if the belt also drives other accessories. Small leaks will not prevent the vehicle from driving, but when fluid cannot be added quickly enough to keep the pump full, a tow truck is recommended to avoid damaging the fuel pump and steering gear.
How often do steering gearboxes need to be replaced?
For most vehicles, the power steering system will last well over 100,000 miles before any failures occur. Mechanical failures and leaks in the power steering system are considered usually avoidable if maintenance has been performed according to the manufacturer service intervals. Keeping the power steering fluid fresh, and the system free of contaminants is the key to ensuring long power steering system life. As any system that carries high pressure will, the system will eventually fail from normal wear and tear, but this should be well into the serviceable life of the vehicle.
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.
Sometimes broken or missing steering gearbox mounting bolts, or loose, worn out steering linkage and/or a cracked frame near the steering gearbox can be confused with the symptoms of a failing steering gearbox.
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.
Other considerations
When replacing a steering gearbox, we recommend using a factory replacement unit. Be sure to verify that the timing and gear ratios are an exact match to the old gearbox.
