Body and Frame: Testing and Inspection
Accident Damage And Diagnosis
General notes
^ Exact diagnosis of the extent of the damage enables proper repair planning.
^ All body repairs must be carried out in accordance with the guidelines in this Body Repair Manual.
^ The stability and strength properties of the body must be taken into account during body repairs. The body has exact defined deformation patterns that must not be affected by any repair work.
^ For instance, the crumple zones absorb the bulk of the impact energy. If any unprofessional repair techniques or methods are used in these areas then this can pose a fundamental threat to vehicle safety.
Hidden damage
^ As well as looking at external indicators like flaked off paint, it is vital to check for hidden body damage or deformation that is not visible from the outside. Large attached parts like bumpers and inner fenders often need to be removed to allow accurate assessment of damage to underlying body parts.
Gap dimensions
Gap dimensions offer another alternative for diagnosis by visual inspection. If any changes or misaligned edges are apparent, then this usually indicates that the dimensions of the affected part are incorrect.
Changes in gap dimension
Impact effects on the body
NOTE: Vehicle components like drive shafts and trailer attachments transfer forces. If a vehicle is subjected to a rear impact then all connected body parts and mechanical components (e.g. transmission mountings) should be thoroughly checked. Electronic components should be checked to ensure that they still operate correctly.
Furthermore it is possible to deduce the overall extent of damage from the direction and magnitude of the impact forces. This does however require extensive body-specific knowledge.
If, for instance, an impact occurs at the front left-hand side member, then the right-hand side member is usually also affected as a result of the rigid body-shell design (crossmember). Often the length of this side member will not have changed, but because of the rigid body-shell design it may have moved from its original position (often only by a very small amount). If any deviations are present this can usually be detected by checking the gap dimensions between door and fender or by checking for changes in dimension.
In the case of more severe impacts, the front part of the body cannot absorb all of the impact energy, and the passenger cell is also deformed. Here the impact energy is transferred via the side member to the A-pillar (see diagram). This results in deformations in the area of the roof and the door rocker panel.
The body reacts quite differently to side impacts where there is hardly any crumple zone. As the passenger cell is extremely stable, there are comparatively few local deformations at the site of the impact. However, the impact forces are transferred to the entire vehicle floor, which often results in so-called "banana damage", where the vehicle is bent into a banana shape.
Impact energy is transferred via the side member to the A-pillar
Body measurements
Measuring options
^ Comparison measurements can also be made on the outside of the body. Depending on the damage, comparison measurements and diagonal measurements can be carried out using compass, telescopic rod, tape measure or ruler.
^ NOTE: The same reference points must be chosen on both sides when checking for changed dimensions (e.g. bores, edges, beads/swage lines etc).
All of the important external body dimensions are listed in Tolerance Checks.
^ Measurements with a measuring/straightening jig.
^ A measuring/straightening jig is required for accurate measurements of the body. The measuring systems are categorized by their means of operation:
^ Mechanical measuring system.
^ Optical measuring system.
Quick and accurate measuring results can be obtained using computerised measuring systems.
A minimum of three intact measuring points on the body are required for measurements of length, width and height dimensions.
In some cases this may mean making the measuring points accessible. All of these measuring systems can be used to make body measurements, provided all the equipment is available.
Planning a repair
The following decisions have to be made before the repairs are started:
^ Does the vehicle need to be put on a straightening jig, or can it be straightened by other means?
^ Does the body need to be measured?
^ Do aggregates like engine or axles need to be removed?
^ NOTE: It is preferable to repair body parts rather than to renew them, as this keeps the complete body-shell intact.
Which body parts need to be renewed?
^ Which body parts can be repaired?
Obtaining spare parts
The availability of spare parts often determines how easily the body repairs can be carried out. The following procedure is recommended:
^ Obtain all the data for the vehicle, including type, vehicle identification number, trim code, engine identification letters, initial registration etc.
^ Establish all of the metal parts that need to be renewed.
^ Establish all of the attached parts that need to be renewed, including small parts like rivets, clips etc.
Straightening repairs
WARNING: The use of heat when pulling to straighten body panels, (such as side members), is not recommended. Longitudinal pulling, (hot or cold), is also not recommended. A small amount of side to side pull is permissible, (cold). When any type of pulling or straightening operation is performed it is important to observe for any movement in adjacent panels. A panel must retain its strength and integrity, if there is any doubt the panel must be renewed.
Straightening repairs are often required to restore the body to its original shape after an accident. This can be done with:
^ Alignment jigs.
^ Universal straightening and measuring jigs.
^ Welding jig system.
The following points must be followed to ensure that the repairs are carried out professionally and that all the dimensions are correct after the repairs have been carried out.
^ Structure: The repair sequence depends on the individual repair plan (taking any necessary disassembly work into account). Clean the attachment areas. Anchor the vehicle free of stress on the relevant system. Support the aggregates to take strain off the body. Decide on at least three measuring/mounting points that are undamaged and as far apart as possible (for basic adjustment). Check the dimensions of the measuring/mounting points.
^ The repair sequence depends on the individual repair plan (taking any necessary disassembly work into account).
^ Clean the attachment areas.
^ Anchor the vehicle free of stress on the relevant system,
^ Support the aggregates to take strain off the body.
^ Decide on at least three measuring/mounting points that are undamaged and as far apart as possible (for basic adjustment),
^ Check the dimensions of the measuring/mounting points.
^ Straightening:
NOTE: Check dimensions and gaps continuously during straightening.
A body is always straightened in the opposite direction to that of the impact. Always carry out straightening repairs with the complete body shell assembled (do not cut out any parts beforehand). Carry out the straightening work in several stages. This prevents the risk of over stretching or of welded joints tearing out. During the individual straightening steps, relieve tension by striking with an aluminium hammer while the part is subjected to a tensile load (in the area of pre-determined folding points, dents, welded joins etc.).
^ NOTE: Check dimensions and gaps continuously during straightening.
A body is always straightened in the opposite direction to that of the impact. Always carry out straightening repairs with the complete body shell assembled (do not cut out any parts beforehand). Carry out the straightening work in several stages. This prevents the risk of over stretching or of welded joints tearing out. During the individual straightening steps, relieve tension by striking with an aluminium hammer while the part is subjected to a tensile load (in the area of pre-determined folding points, dents, welded joins etc.).
^ Special features: Ultra high strength steel cannot be straightened due to its brittleness and must always be replaced.
^ Ultra high strength steel cannot be straightened due to its brittleness and must always be replaced.
Cutting out body parts
Depending on how the parts are joined/connected, different tools are suitable for cutting/separating body parts.