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The Knowledge – Hidden corrosion

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We have been receiving a number of enquires about suspension and sub frame mountings particularly with regard to corrosion. Those of you who have been testing for more than a few years will remember the good old days of corroded sills and body panels. While modern galvanising and painting systems have done much to improve this area of vehicle manufacture, corrosion can still be a major problem where we may least expect it.

It’s not just thin body panels that can suffer the effects of corrosion over time. Many suspension components and sub-frame assemblies are often hot spots for corrosion in areas which can be difficult to access or examine, so extra care should be taken.

So how should we be checking them? Well, initially by visual inspection and finger and thumb pressure, but remember we can also use the corrosion assessment tool to lightly tap and scrape where corrosion may be localised.

The picture above of a rear suspension shows what could be hidden under the surface dirt. Clearly this example has been corroded for some time but it does show how it would appear in surfaces you may not expect. Remember that a suspension arm such as this would be considered a highly stressed component – so it should be rejected if corrosion has resulted in a serious reduction in the overall thickness of the material, or has caused a hole or split.

Thin gauge pressings are often used in the manufacture of some suspension components, mountings, and sub-frames. These are often complex shapes with open or hollow sections which collect road dirt with salt or other chemicals causing serious localised corrosion. These types of components require extra care as there may be little evidence of corrosion on initial inspection, but may reveal severe material failure when looked at more closely.

See Appendix C of the Inspection Manual for more detail on how to inspect and assess corrosion in components as well as in structural and body panels.

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