97 MXV wrote:My previous post identified the death roll about two opposing load supporting stands causing them to be ejected and the car coming down on top of its victims.
Adding extra unloaded backup arresting stands to restrain the car before it rolls appreciably is an option provided we are totally confident they will not fail on demand, that is they must not fail to arrest the car at the critical time needed when they transition from unloaded to loaded while people are under the car.
Eureka we now have the smoking gun ! An actual event in a different but same context.
One of the forum members who I will not name, had a near miss years ago when an MX5 being worked on whilst raised up in the air, totally unexpectedly slid completely (yes completely) off its 2 post, 4 point style hoist like this in a death roll on just two of its supports (diagonally opposite each other as explained earlier).
It literally rolled and slid diagonally off the hoist because the safety lock restraining one of the other support arms from swinging out from under the car, was not functioning at the time (for reasons undisclosed). The MX5 was supported at the jacking points in a similar configuration examined in yesterday's posts.
The full sequence of events is not entirely clear but involved weight shifting back and forth between the unrestrained support arm and its diagonally opposite number exacerbated by removal and replacement of heavy items like wheels for example. In that process, somehow the unrestrained and obviously unloaded arm found itself swung out just enough to create a faulty support surface for when the load came back on (by say removal of tyres on the other side) just
Seconds from Disaster.
Eventually and inevitability, the weight came down on that faulty support and it suffered a functional
Failure on Demand by dislodging further sideways with no warning. The now absence of a support function from underneath, allowed the death roll to then run to its full completion under that relentless force of nature,
we call gravity.
The helpless forum member could only look in agonizing disbelief as the house of cards came tumbling down with
no apparent cause for the car to suddenly and inexplicably roll over and suicide dive off the hoist into such devastation and calamity reverberating all around him.
It was a wake up call to better maintain the safety lock on the swing arm and to always pre-adjust for even contact, all 4 support pads up under the body of the MX5 using the threaded adjustment provided before raising the car; then once in the air check them again for a nice snug fit up at all four points and check the centre of gravity does not move too far forward or rearward while fitting and removing heavy objects like transmissions and diffs, because our good friend Kyle sure knows how
to lift it right !