A gearbox assembly for all electric power steering apparatus comprises an input shaft which carries a worm gear and is supported relative to the housing at one end by a first bearing assembly and at the other by a second bearing assembly, an output shaft which carries a wheel gear which is fixed relative to a housing and which meshes with a worm gear on the input shaft, and a spring assembly which acts between the housing and the first bearing assembly, and the spring assembly applying a biasing force onto the second bearing in a first direction away from the neutral position so as to ensure that the worm and wheel are fully engaged. The spring assembly has a spring rate which has a step change about the neutral position such that the rate of change in the force exerted by the spring assembly on the second bearing assembly as the spring moves in the first direction from its neutral position is lower than the rate of change in the force as the spring moves in the second direction away from the neutral position.