The steering column is constructed so that the mast jacket, shift tube and steering shaft will collapse individually under various front impact conditions. An expanded metal section at the mast jacket, located below the instrument panel permits the column to collapse. The steering shaft is a multiple-piece design having a flattened oval upper shaft staked in a hollow lower shaft. The shifter tube is fabricated from three separate sections. Unitizing of the steering shaft and the shifter tube is achieved by injecting plastic into adjacent cavaities in each part.
To function as an energy absorbing column, the column must be free of its attachment at the instrument panel and firmly held at the bottom end. The column-to-instrument panel retaining bracket is shear mounted to the instrument panel.
The steering column-to-instrument panel retaining bracket is rigidly fastened to the mast jacket. The bracket is bolt attached to the insturment panel through retainers which are an integral part of the bracket. Retainers are integral with the bracket through an injection molding process which forms plastic shear-pins. Controlled release of the column is established by a predeterminded load being placed on the shear pins. Located in open-ended slots in the bracket, the retainers serve as a guide to allow the column to move in a downward direction.
Servicing the Energy Absorbing Steering Column (fig 37) can be accomplished easily. You should be aware that only the specified screws, bolts and nuts be used as designated during reassembly, and the the bolts are tightened to specified torques. this precaution will ensure that the energy absorbing characteristics are not destroyed. Care should also be exercised to ensure that overlength bolts are not used, as they may prevent the assembly from compressing under impact.
When the column is installed in a vehicle, it is no more susceptible to damage through usage than an ordinary column; however, when the column is removed from the vehicle special care must be exercised in handling. Such actions as a sharp blow on the end of the steering shaft or shift levers, leaning on the column or dropping the assembly could shear or possibly loosen the plastic fasteners that maintain column rigidty and therby destroy future utility. It is important that the service procedures be carefully followed.
source; Chevrolet Service News Volume 38 September - October 1966 Number 9