BINGO...........
Dave,
Chassis in the early '90s were a poo poo load stronger, thicker, designed, fabricated etc than today's crop of wafer thin steel pretending to be a chassis........add in the fulcrum effect and you get...........snap........
I have just reread this whole thread from wo to go, the above statement made way back in October 16, 2013, nearly hit the nail on its head.
Yes I agree that air bags can and do have some affect of chassis bending/breaking and yes I agree with Metters and his statement from October 21, 2013.
But the earlier 4x4's including the 60 series and the Nissan GQ range had chassis made from mild steel and were thickr than modern chassis.
The newer late 90,s onward 4x4's went to lighter, thinner HIGH TENSILE steel to build their chassis with.
High tensile chassis are in fact stronger than their heaver MILD steel cousins, but unlike mild steel ( if not made thick/strong enough they will bend, but seldom break ) , HIGH TENSILE steel fatigues with constant flexing ( same as Stainless Steel ) and in time the high tensile steel will develop cracks , the cracks weaken the chassis design and will fail.
In the mining industry, particularly the underground industry , the average age of a vehicle ( mainly Toyota Landcruisers are used in this industry ) , is only a couple of years before the chassis fail and the vehicle becomes land fill. No air bags , not that much in the way of overload, but constant flexing of the chassis.