What is knocking in my Ford Transit steering over bumps?

A knock from the front over uneven roads and play felt through the steering wheel have several common causes on the Transit MK6 and MK7, and it makes sense to check them from the least expensive upwards. Begin with the anti-roll bar links and bushes, which can produce the classic clunk at full steering lock and over speed bumps, followed by the outer tie-rod ends. If these are sound, remove the steering rack gaiter and check the inner tie-rod joint. This frequently overlooked part cannot be seen without removing the gaiter. Also inspect the lower ball joint and wishbone bushes. One fault reported repeatedly on forums is a bush separating from the wishbone arm, allowing the arm to knock against the subframe. In that case, replace the wishbones in pairs, preferably together with the ball joints.

Does play in the steering rack mean the whole rack must be replaced?

Usually not. The inner tie-rod joint screws into the rack and can be replaced separately, making this a quick repair at a fraction of the price of a complete steering rack. Replace the whole rack only when the play is in the rack bar itself, which can be checked by holding the bar with the gaiter removed, or after a kerb impact has bent the rack. Wheel alignment is essential after any work on the tie rods. After replacing the steering rack, bleed the power steering system by turning the wheel from lock to lock with the front of the van raised.