Why Austin Seven Rear Springs Break?
The following three photographs show a broken rear spring recently discovered on my Austin Seven (after a loud bang was heard from the rear of the car). Upon closer inspection the bottom leaf was found to have fractured completely.
This photograph shows that the leaf had been partly fractured previously, most likely for years before finally letting go.
So why did it break there?
After talking to the local spring maker his theory is that the breaks occur as a result of the upwards travel being limited by the deep groove worn into the spring as shown above. The end of the next leaf restricts the upward movement when it hits the end of the groove in the bottom leaf. This will only occur when going over a largish bump. Extra forces are placed on the bottom leaf as a result. This cutting of the groove occurs over a long time as the leafs rub together. From my experience the formation of the groove seems far greater on the leafs with tapered rounded ends vs the plain square cut ends I have on some samples. I would highly recommend checking for deep grooves in this area and if necessary consider having some replacement bottom leafs made up. It is a strange feeling to have 1/2 the differential floating around and cornering at speed is positively scary! SO, it is not only the steering arm we need to worry about on these old cars.....
Photographs thanks to Rod Wells - 2003