Quote:
Originally Posted by Private_collector
This little crack will need repair regardless. It has seen some dreadful treatment in the past?
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Quite possibly, but I suspect the principal cause of blitz chassis failure is removal of the original body. The loss of rigidity leads to enormous flexion in the rear chassis, which is really quite spindly, esp. the Ford rear chassis. Also the loss of weight over the rear axle means the springs are virtually rigid, so the rear chassis simply twists back and forth over uneven ground, eventually causing fatigue cracks. We rarely see a bent chassis from overloading, but it's common to see fatigue cracks from constant torsion. Of course, with a dodgy crane fitted, the torsion forces can be massive.
Another area subject to repetitive torsion is the front chassis under the steering box. The chassis rail is only single skin at this point, and it has to support the engine mount on one side, and the spring hanger on the other side, plus the back and forth steering wheel force multiplied 20+ times through the steering box. Pics below show a fatigue crack in this area on a F60L chassis I scrapped recently. As you can see it has progressed almost half way through the chassis rail....imagine the consequences of sudden total failure at speed!