Subject:
Steering Column
Topic:
Steering Column: Part 2 - Rack-and-Pinion Steering Column Design Features
Objective:
Identify by name the design and major components of vehicle steering columns and explain how these features influence vehicle rescue operations
Task:
Given vehicles of different makes and models, name the type of steering column and explain how components of the column can influence vehicle rescue operations
A different and more common type of steering column design that may be found at a vehicle rescue incident is also a more complex one. Known officially as a rack-and-pinion steering column, this multi-piece steering column became popular in about 1980 with the popularity of front-wheel-drive vehicles. Rescuers typically refer to this column design as a "split" column.
The tell-tale sign that rescuers are confronted by a rack-and-pinion steering column is when a flexible knuckle joint can be seen at the point where the steering column penetrates the floorboard area. The knuckle joint connects the upper shaft to a shorter second portion of the column. Not all split steering columns have a knuckle joint and not all split column knuckle joints are visible within the column assembly.
In an extrication situation, the upper portion of a split column will bend up and away from the trapped driver as a pulling tool is put into action. The concern with the split column is just that, the fact that it is split. The lower sections around the knuckle joint can move in opposite and possibly unwanted directions during the column pull. Rescuers must watch both the action and the reaction movement when a split column is moving.
There was a concern in the early 1980s, when rack-and-pinion steering columns became popular. This concern materialized into nothing more than an urban legend. The caution was that the bottom portions of the column at the knuckle joint would fly apart violently during a column pull and impale into the trapped driver. This concern is unfounded. During a column pull, although the knuckle joint may move in an unexpected or unwanted direction, the lower sections of the split column don't blow apart when over-stressed. The lower sections simply slide apart harmlessly.
Ron Moore, a Firehouse contributing editor, is a battalion chief and the training officer for the McKinney, TX, Fire Department. He also authors a monthly online article in the Firehouse.com "MembersZone" and serves as the Forum Moderator for the extrication section of the Firehouse.com website. Moore can be contacted directly at [email protected].
