Steering (Steering Rack): Description and operation (page 2 of 2)

The steering rack is unique in having the track rods mounted at a central location on the rack. The track rods are very long and combined with the optimized steering geometry provide low levels of 'bump steer'.

The steering rack is mounted in the engine compartment on the lower part of the bulkhead. The rack is retained with two bolts through cast lugs near the valve unit and two bolts which secure a clamp over the opposite end of the rack. The lower bolt through the cast lug is fitted with a large washer. The steering rack is handed for left and right hand drive vehicles.

The rack requires 3.2 turns from lock to lock and the rack and pinion has an overall ratio of 19.6 : 1.

A valve unit is fitted to one end of the steering rack and connects, via a splined input shaft, to the adaptor of the steering column. The valve unit has four hydraulic connections; a pressure feed from the PAS pump, a return line to the reservoir and two pressure lines to the annulus and full area of the hydraulic cylinder.

An input shaft, installed through the valve unit, is connected to a pinion gear which drives on a rack which, in turn is connected to the piston rod in the hydraulic cylinder.

At a central position on the rack are two threaded holes which allow for the attachment of the track rods. Rubber bellows cover the movement area of the rack.

Two hydraulic ports, one at each end of the hydraulic cylinder of the rack, are connected by metal pipes to the valve unit. The ports supply hydraulic pressure to the annulus and full area of the cylinder. The annulus end of the cylinder is supplied with PAS pump outlet pressure and the full area end of the cylinder is supplied with pressure regulated by the valve unit. The cylinder end of the piston rod is fitted with a piston which houses a piston seal.

The track rods are fitted with rubber bushes which are hard enough to give positive feel to the steering but at the same time reduce unwanted feedback through the track rod. Each track rod is fitted with a track rod end. The track rod end is a ball joint which locates on an extended bracket on the suspension strut and secured with a lock nut. A turnbuckle is screwed into the track rod and the track rod end and allows for the adjustment of the steering alignment.

The track rods are located on a bushed slider which locates on the rack. Two spacers are located between the slider and the track rods. Two flanged bolts secure the track rods to the rack.