self inflicted steering problem - any ideas?

If the steering wheel centring changed in the circumstances you describe, then you would appear to have "done something". I would look for either a broken centre bolt, a bent track rod or drag link (either side of the relay) and failing that I would suspect that one of the arms on the top or bottom of the steering relay has skipped a tooth on the spline - if this is the case you may have to replace both the arm and the shaft. Other possibilities include the steering wheel having moved on the shaft - the spline on this is not necessarily tight, and the drive should be taken on the taper, so it could have turned by the slack in the spline. Other long shots include a loose steering arm, ball joint shifted in its tube, broken spring, steering box or its support moved. The screech was probably the tyre hitting something, such as a spring or the body. Thinking about it, I expect that a broken centre bolt is the most likely, as it is the only one that would allow the wheel to hit the spring or body, although your steering stops may be wrongly adjusted, allowing the contact to be made in extreme conditions. JD

Assuming there's no obvious external damage, the it could well be that one of the half-shaft uj's has broken up and one or more cups has fallen into the bottom of the swivel housing. This will then prevent that swivel ball turning properly.

One way to check, though not as good as having a look inside, is to turn the steering towards the affected side as far as you can while stationary. If you can then "wind up" the steering, such that the wheel whips back through your hands (mind those fingers) then that can indicate a uj problem.

Cheers Richard