GM Service Manual Online
For 1990-2009 cars only

Tram Gauge Method

    â€¢ Use a tram gauge as a quick reference in order to determine vehicle damage. Use a tram gauge set with a vertical pointer capable of reaching 914 mm (36 in).
    â€¢ Make the engine compartment component measurements from point to point with the vertical pointers equally set.
    â€¢ Make the other measurements on the horizontal plane, or the datum line, parallel to the underbody with the vertical pointers set as specified for each point.
    â€¢ Measure dimensions that are measured to the gauge holes to the center of the holes and flush to the adjacent surface metal unless otherwise specified. Cross-check the diagonal dimensions in order to verify the dimensional accuracy of the vehicle underbody.

3-Dimensional Method

    â€¢ Measure following multiple points when measuring structural repair with repair equipment:
      â€¢ The length
      â€¢ The height
      â€¢ The width
    â€¢ Measure 2/3 of the vehicle body in order to obtain accurate comparisons to the vehicle structure.
    â€¢ Univeral measuring systems combine the equipment and the techniques used to make the underbody 3-dimensional measurements. The universal system provides accurate measurements of the following points:
      â€¢ The length
      â€¢ The width
      â€¢ The height