I had the same problem which I cured with the following information posted on the Sevens list:
Where the column enters the rack, at 90 degrees to the column there is a big
adjuster secured with a lock nut. BEFORE YOU DO ANYTHING ELSE, mark the
current position of the adjuster (to the lock ring and to the rack body)
using tip-ex or some such substance. You can then loosen the lock nut (big
adjustable spanner) and adjust the mesh of the rack and pinion (Allen key).
Because tightening the lock ring changes the meshing slightly, you have to
move the adjustment by small amounts tighten it up and test with each
adjustment. You shouldn't test for slack, but for the onset of *noticeable*
friction. Mine needed adjustment of about 3mm at the circumference of the
adjuster (hence the tip-ex mark). The tip-ex also means that you can remove
the adjuster entirely to have a look at what it does inside the rack and get
it back to approximately the right place to start the fine adjustment.
Testing needs as little mass as possible to be attached to the system. You
can do this by knocking the rod ends out of both steering arms and taking
your wheel off. It would be better if you didn't have te column attached,
but it is not entirely necessary as it has a low moment of inertia. You can
do all of this with the rack in the car.
Testing involves moving the rack through its range of movement by pushing
and pulling on one track rod. The friction in the system is much more
apparent here than at the steering wheel. You should ignore resistance at
the very ends of the rack travel as the compression of the boots starts
having an effect, with air wheezing in and out. The majority of the travel
should be free running. Adjust until you feel the friction and then back
off by the width of a gnat's tadger.