The steering box on your 4WD probably gets little attention compared with all the other parts of your rig. However, you use the steering box constantly, and if it's not performing reasonably well, you'll quickly know it. Symptoms can range from a slight annoying wander as you drive down the highway to a death wobble that slaps your steering wheel back and forth in a demonic way. Any of these traits could be the result of a maladjusted or worn steering box.
Steering Box Troubleshooting
Trying to solve steering issues can sometimes be difficult. With much of the weight of your 4WD bearing down on the front axle and possible issues with wheels and tires, isolating specific steering problems takes a little thought and checking of components. If you're confident the problem does not lie with your tires or their balance, you should proceed to inspecting the steering components.
It may be best to check other steering components before checking the steering box. A quick check of the tie-rod ends, wheel-bearing play, and ball joints or knuckle bearings can be done. Any play in these components can cause looseness and wander in the steering. At the steering box, turn the steering shaft back and forth slightly by hand and observe the movement of the pitman arm. There should be little free-play in the steering shaft, and the pitman should move immediately, matching the movement of the steering shaft. If there is excessive free-play or looseness, then the steering box needs adjustment or repair.
Steering Box Maintenance/Repair
Over time, all steering components wear with use, including the steering box. Fluid changes can help somewhat, but it's usually not necessary to change the fluid often unless it has been contaminated with water due to submersion. Some slight play may develop in the mechanism, causing your vehicle to wander from side to side. This can become annoying, unnerving, and, eventually, unsafe.
Many steering boxes can be adjusted to remove the excessive play in the gear mechanism. With simple instructions found in most service manuals, many steering boxes can be adjusted by most home mechanics using a few common handtools. Time and mileage, however, will eventually take their toll on the internal components. Seals will also age, dry, and begin to seep fluid. Once this occurs, you'll need to consider a replacement or rebuild.
Some steering boxes can be rebuilt by a do-it-yourselfer without specialty tools, while other units may require special tools to effectively complete the rebuild. A thorough reading of a service manual will show you the details and tools needed. In any case, rebuilding a steering box requires patience and the assembly of many small parts and seals. Cleanliness and attention to detail will help ensure that the result is a quality rebuild.
The hydraulic ram is mounted to the front axlehousing and uses the high-pressure fluid routed from the steering box to assist with pushing the tie rod.
Along with the maintenance of your steering box, periodically inspect other related components, such as the steering shaft and U-joints, couplers, pump, and hoses. There's no need to put a damper on your day due to badly worn or failed steering components. Follow along with the photos to get an idea of the nature of the internal parts of a common Saginaw recirculating-ball power-steering box.
In recent years, hydraulic-assist and full-hydraulic steering systems have become more common on 4WD vehicles that see hard-core trail use and ride on large tires. A hydraulic-assist system retains the mechanical steering linkages and supplements the mechanical action with additional hydraulic force from an axle-mounted cylinder. The cylinder is connected to two fluid ports tapped into a stock-type power-steering box. Within the box are two areas, each where high pressure exists when the box is turned one way or the other. Hoses tapped into these areas are plumbed to the assist cylinder.
To run a hydraulic-assist steering system, the power-steering box must be drilled and tapped to access fluid pressure used to push the ram one direction or the other.
Hydraulic assist provides considerably more steering power assist and reduces required driver input and driver fatigue. Steering large tires on smooth terrain becomes a one-finger job, and steering in a boulder field now becomes much less tiring. Additionally, hydraulic assist removes some of the steering strain from the framerail, where the steering box is mounted. This is a common area of fatigue cracking for rigs used on hard-core trails. Companies such as AGR Performance and West Texas Off Road offer assist kits for a number of 4WD vehicles.
Full-hydraulic steering eliminates the steering box and associated mechanical linkages, replacing them with an orbital valve at the steering column attached to the steering wheel. This can be located near the firewall and eliminates the steering shaft running through the engine compartment. An axle-mounted hydraulic ram moves connector links, which attach directly to the steering arms at the axle knuckles. Full-hydraulic steering offers the greatest ease of steering large tires under extreme conditions. The drawbacks, however, include greater cost and the fact that full-hydraulic systems are not typically street-legal.
This is the steering input end of a typical Saginaw power-steering box. This splined shaft will usually mate to a universal joint or rag-joint flange connecting to your steering column. You can also see the high- and low-pressure hose connection points. | 
The sector shaft is the output of the steering box. This splined shaft exits the bottom of the box, and the pitman arm attaches here. A steering tie rod then attaches to the pitman arm. | 
Steering boxes are most often bolted to the forward framerail using three to four bolts. These should be checked periodically. Loose bolts can cause steering play, frame cracks, or broken mounting tabs on the box. |
On the top plate, an adjustment stud and jamb nut are used to adjust the amount of play in the sector shaft. Your service manual should describe how to adjust the sector shaft to remove excess free-play from the steering box. | 
Here, you can see the sector shaft removed from the box. It rotates on a set of needle bearings. Several seals and metal washers are secured around the shaft using a snap ring. | 
The upper end of the sector shaft contains several gear teeth. They mesh with matching teeth on the power piston, which is located in the main portion of the steering box. |
Here is the rest of the disassembled box. The components in the main portion of the box are (left to right) the power piston, worm gear, and input shaft assembly. | 
The splined input shaft enters the box through an adjustment nut and sealed head assembly. Several seals are needed to retain the high-pressure fluid within the box. | 
The worm gear lies right in the middle of the recirculating ball assembly. Ball bearings move along its spiral body, which serves as an inner-bearing race. |
The power piston is machined with an internal spiral to mate to the ball bearings and worm gear. Here, the couple dozen balls move, or recirculate, through a tubing assembly. When the input shaft and worm gear are turned, the power piston moves back and forth inside the box housing. On the outside of the power piston are four teeth, which mesh with those on the sector shaft. As the power piston moves, the sector shaft and pitman arm rotate. | 
Numerous seals are used throughout the steering box as internal fluid pressure can exceed 1,000 psi. When rebuilding a box, all these seals are replaced, along with some washers and possibly the sector shaft bearing. | |