What causes a knock through the steering on a Ford Transit over bumps?

Front-end knocking over rough surfaces together with free play felt at the steering wheel has several familiar causes on MK6 and MK7 Transits. Work through them in order of cost. Inspect the anti-roll bar drop links and bushes first, especially where there is a typical clunk at full lock or over speed humps, then check the outer track-rod ends. If these parts are tight, remove the steering rack gaiter to test the inner track-rod joint, an often missed component that cannot be properly seen with the gaiter fitted. Include the lower ball joint and wishbone bushes in the inspection. Forum cases also describe a bush separating from the wishbone, allowing the arm to strike the subframe; when this occurs, replace both wishbones, preferably with new ball joints at the same time.

Does steering rack play always require a complete replacement rack?

No, in most cases it does not. The inner track-rod joint is screwed into the rack bar and is available separately, making replacement much quicker and considerably cheaper than fitting an entire steering rack. A complete rack is justified only when movement is within the toothed rack bar itself, checked by gripping it after removing the gaiter, or when a kerb impact has bent the rack. Any work on the track rods must be followed by wheel alignment. If the rack is replaced, bleed the power steering with the front raised by turning the steering repeatedly from full lock to full lock.