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 didn’t
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 couldn’t 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 ‘Austinspeak’,
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 I’ve 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 doesn’t 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 owner’s 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 3/8” 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 wouldn’t
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. I’d
bought a set of these, brand new, for no particular reason, when I’d seen
them going cheap on a rally field. Sometimes the old fashioned tools are the
only ones that’ll do. I’ve 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 wasn’t 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 didn’t 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 that’s 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
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The steering box |
showing the nut to be loosened | |
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