5-101.bk Page 5 Friday, March 17, 2006 11:05 AM FASTENER TORQUE Proper installation is as important as the selection of the correct fastener. Improperly installing a correct fastener is just as bad as using an incorrect one. Undertightening and overtightening both result in an improperly installed fastener. When threaded fasteners are tightened, a slight stretching of the fastener occurs, and it is this stretching that binds the assembly together. If too little tightening occurs, the slight stretching does not happen, and the joint is not clamped securely. If too much tightening occurs, the fastener will be excessively stretched, causing narrowing of the fastener and possibly breaking.
Correct and consistent use of a torque wrench ensures the fasteners are properly tightened, and clamping the pieces of the assembly together. Fastener Selection and Installation Selection and correct installation of threaded fasteners are essential parts of any assembly or rebuild procedure. Fasteners hold much of a vehicle together. If a fastener fails to do its job properly, it can cause a minor problem such as a loose mirror, or a large problem, such as loss of steering control. Because there are so many styles of fasteners, in various sizes and quality grades, a mechanic must have a working familiarity with the fasteners commonly used in vehicles.
Only in this way can the correct selection and installation of the proper fastener be ensured. Each fastener is intended to do a particular job, and is selected by the vehicle manufacturer for its suitability for that job. Figure 2-1 — Fastener Grading System Page 2-5 200 SPECIFICATIONS