Half-shaft failures are more often caused by a loose fit between shaft and rear hub, although some are caused by metal fatigue and the shaft breaks straight across. This may be due to worn hub bearings allowing a twisting moment on the end of the shaft.
The following photos show broken keyways due
to slack hub fitting and a shaft failure (on view) together with a potential
failure due to a radial crack.
This article, written by Anon, originally appeared in CA7C Seven Focus.