In 1976, the Big Ben has its first and only major breakdown. The speed regulator of the chiming mechanism finally broke after 100+ years of torsional fatigue, then the fully-wound 4 ton weights dumped their entire potential energy into the chiming mechanism in one go. It caused a great deal of damage; the Great Clock was shut down for a total of 26 days over nine months - it was reactivated on 9 May 1977; this was its longest break in operation since it was built. __