Notes on steering box overhaul

These notes relate to the Rolls-Royce designed and manufactured steering box. In this design a nut carrying an Acme-style thread runs along a worm which is integral with the central steering column. The nut is lined internally with a layer of white metal, having a thickness of about 0.025".

The notes do not apply to the later 'Marles' steering box.

1 Typical symptoms of a steering box in need of overhaul:

  • Steering sticking on a lock and not self-centering.
  • Problem might be worse after a period of driving, when the engine heat has been absorbed by the steering box.
  • When the car is stationary, it can be possible to pull the steering wheel in one direction or the other, against the resistance of the tyres, and on release the steering wheel will stay or stick in that position.

2 Before condemning the steering box, it is most important that all the steering pivots are checked and confirmed to be free of excess friction. Checking the freedom of the steering with the front wheels off the ground and with no load on them is not adequate - the weight of the car must be on the front wheels. Steering box problems should not be confused with steering which is heavy in operation for other reasons, such as poor lubrication of the kingpins.

3 If the indications are that the steering box is the problem, before embarking on an overhaul of the box check

  • that the column is not being strained by the supporting clamp fitted to the reverse side of the bulkhead.
  • that the self-aligning ball race at the top of the outer column is correctly adjusted (free with no perceptible end-float) and lubricated (normally greased on assembly), and not over-tightened.
  • Experiment with a variety of lubricants. Note that an EP oil has no advantage over a straight gear oil in this context.

4 A full mechanical overhaul of the steering box includes

  • Re-sizing the steering nut with a special tap, which exposes fresh whitemetal over all internal surfaces of the nut, and restores the nut to a known geometry;
  • Removing the original worm from the shaft, and fitting a new oversize worm, made to suit the re-sized nut.
  • The worm and nut are lapped together to ensure the best performance is obtained from the combination of worm and nut.
  • Any other work which is considered necessary to restore the performance of the steering box, particularly by the replacement of other worn or damaged parts which might contribute to excessive free play in the steering.

5 We can recommend trusted specialists to overhaul your steering box.