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Adjusting the steering box

When our 1931 Austin Heavy 12 went for her MOT test last year, she passed without any hitches, but my tester gave me an advisory notice of excess play in the steering drag link. I had known of course that there was some play in the steering gear, but I didnít think it was at the drag link. Still as it was only an advisory this time, I knew I had a whole year to investigate and put things right. On several occasions, while under the car, in the months that followed, I tried to feel for the play in the drag link, but each time I couldnít find any. I started to wonder if we were talking about the same thing or were we at cross purposes.
In the Austin 12 Spare Parts List, Austin use terms that are not very helpful to identify the steering parts, which could be known by other names. In ĎAustinspeakí, the arm attached to the steering box is the steering arm, but I would call it the drop arm. The arm connecting the steering arm to the offside swivel axle, they call the steering side tube, but I would call this the drag link. The arm connected between the two swivel axles, they call the steering cross tube, but Iíve always known this as the track rod. The arm that connects the front end of the drag link to the off-side swivel axle is called the side tube swivel arm by Austin, but I would call it the steering arm. All very confusing, and the average MOT tester doesnít often have to deal with parts like these nowadays anyway, so what chance has he got ?
Anyway, I started thinking he may have identified some play elsewhere but misled me with the name. I checked the other parts in the system, particularly the track rod for wear, but found none in any of the linkages, from steering box to kingpins and wheel bearings. The only free play I could identify was all in the steering box itself. I had assumed that this would be all down to wear, and started to panic. But I studied the diagrams in the Parts List and checked what it said in the ownerís handbook, and there was a section on steering adjustment. So perhaps it would be possible to take up some of the slack by adjustment.
It seems that provision is made in the steering box to adjust the meshing between the worm and worm wheel, the worm being on the steering column and the worm wheel being mounted on a shaft at right angles to it, across the steering box. This shaft runs in an eccentric steel bush in the steering box housing, and by turning the bush, the shaft and worm wheel can be moved to bring the worm wheel more into mesh with the worm and reduce the free play. The worm wheel has a screw thread cut around its external circumference, and a long bolt running vertically through the housing, meshes with it. This bolt can be found close to, and just forward of the top of the drop arm. The bolt head is at the bottom of the steering box, with a nut and lock washer at the top. The lock washer must first be loosened from above, and then when the bolt head is turned from below, it acts to turn the eccentric bush in the housing.
I started by jacking up the front axle and putting it on axle stands with the front wheels on, but clear of the floor. To get the feel of how the steering should be, I wound the steering wheel from lock to lock several times, taking note of how much effort was needed and making sure there was no sign of binding at any point. Now it was time to get at the adjusting bolt and its locknut. I found the 3/8Ē Whit nut at the top was well painted over and very close into the body of the steering box. This looked like a problem straight away, because there was no room for a modern socket spanner, a ring spanner wouldnít go over the nut, and there was no room to swing an open ended spanner. Eventually, I found an old fashioned box spanner which just fitted and did the job. Iíd bought a set of these, brand new, for no particular reason, when Iíd seen them going cheap on a rally field. Sometimes the old fashioned tools are the only ones thatíll do. Iíve found the same with axle hub nuts in the past, so I collect all the large, old rusty box spanners I come across, usually for 50 pence each, just in case !! With the nut loosened off, its time to get under and look for the head of the bolt. More problems here because the steering box wasnít visible from below, as it was covered by one of the engine cover plates which had to be taken off. After that the head of the adjusting bolt was easily accessible and just needed the paint scraping off so that a standard socket could be used to turn it.
I had no idea how far the bolt would need turning to make the adjustment, but it needs to be turned clockwise to make a closer mesh between the worm and worm wheel. I started by giving it about half a turn, which didnít seem to make much difference, so I kept turning it a little at a time, and checking how the steering felt each time, by winding it lock to lock. A point will be reached when the steering may feel OK with the wheels near the straight ahead position, but will bind when nearing full lock. By adjusting by small amounts and testing, I took up as much of the play as I could without causing any binding at full lock. After that, all thatís needed is to re-tighten the lock nut on the top. This seemed to reduce the free play at the steering wheel rim quite substantially.
There are two other adjustments available on the steering box, for setting the clearances in the thrust races for the worm and worm wheel. These adjustments are not so easy to set, and I decided to leave well alone on this occasion.
The two photos that accompany these notes show the top of the steering box. The brass ring on the left is the thrust adjusting ring for the worm, which should be turned anti clockwise, looking from the top, to reduce the end float, after loosening the four set screws that secure it. The point of the screwdriver shows the nut on the top of the adjusting bolt.
After lowering the car back down to the ground, it was time for a test drive round the block to make sure everything felt right.

Tom Stapledon

January 2007

The steering box
showing the nut to be loosened