Land Rover Defender Steering Box Rebuild Process
The Defender steering box takes quite a beating when driving over rough terrain. A full and proper rebuild of a steering box is a lot more involved than just replacing the seals. Here is a step by step guide to a full Defender steering box rebuild.
Strip-Down and Cleaning
The box is drained of oil and then disassembled. It is taken apart piece by piece so that all parts can be inspected. The whole of the steering box is then taken apart and every single part, the housing, the two shafts, the two bearings and the spacers, are thoroughly cleaned in a suitable solvent to remove any dirt that may have got onto the worn surfaces. If this is not done then it will not be possible to accurately assess the condition of the worn parts.
Inspecting the Shafts and Bearings
The worm shaft is inspected for signs of pitting, scoring and wear of the individual grooves on the helical face. The sector shaft is inspected for wear of the teeth and any excessive side play in the housing bore. The taper roller bearings are inspected for any signs of pitting and given a rub test. If any of the bearings show any roughness then they must be replaced as it is impossible to set the correct pre-load on worn bearings.
Replacing Seals, O-Rings, and Bushes
All seals and O-rings are replaced as new, regardless of appearance. The sector shaft bush is measured for wear, and replaced if the sector shaft has any signs of rock in it. The thrust washers are inspected for thickness, and replaced if below the manufacturers’ tolerance.
Setting Worm Shaft Pre-Load
The worm shaft pre-load is set by shim adjustment at the bearing housing during reassembly. The pre-load is measured by the amount of drag or torque required to smoothly rotate the worm shaft. This must be set correctly to avoid two main problems; excessive looseness will cause the vehicle to wander whilst steering, and excessive tightness will cause the box to overheat and wear prematurely. The pre-load is set to the manufacturer’s recommended specification.
Sector Shaft Mesh and Final Testing
Once the worm shaft pre-load has been set the sector shaft can be assembled and the sector shaft mesh set using the mesh adjuster screw on the top cover of the steering box. This is set to the middle of the turn when the greatest wear occurs. Once the sector shaft has been assembled the steering box is filled with the correct oil and then subjected to a bench test to check for smooth movement through full lock-to-lock and for any signs of leaks. On the vehicle a road test will reveal any play or excessive heaviness when straight, through the straight-ahead position.
A careful rebuild of all the stages outlined above will give the Land Rover Defender Steering Box a life similar to that of a new unit.