Sunday, Jun 03, 2012 at 17:07
Axle - You obviously didn't see the video of the D10 Cat dozer pulling the near-new Brambles Mack apart (taken in the early '90's), in the Northern Goldfields of W.A. (the video doesn't seem to be around anymore, and it did make "Australia's Funniest
Home Videos").
To recap, the Brambles float driver arrived at a minesite with a near new Mack, pulling a platform low-loader, to move a big mining excavator (I seem to recall the ekky was around 150 tonnes).
They dug a bit of a depression (about 300mm deep) and backed the platform float into it, so the ekky could climb on easier.
When the Mack went to drive out, she couldn't get enough traction to pull the float out of the slight hole it was in.
So all the smart boys called up the bloke on the D10 to come and assist the Mack out of the low spot with a tow.
They duly backed the D10 up to the Mack, attached the hefty tow chain to the "proper", factory-installed tow hitch, that was mounted in the centre of the bullbar (and which was firmly attached to the front chassis cross-member).
At the "go" signal, the smart dozer operator roared off, full throttle - and the entire front pull hitch, front chassis cross-member, radiator, grille, and all associated components - all parted company with the Mack!
What happened was that the severe overload on the hitch simply guillotined all the rivets holding the front chassis cross-member, and its angled braces, in place - and the entire front section of the Mack, just took off by itself!
'Twas rather embarrassing for Brambles, and the dozer operator, and the entire crew - when the video made the rounds for everyone to have a good guffaw at!
The simple fact was the combined gross combination weight of the Mack & float (probably around 180-200 tonnes), plus the small depression, added up to a drawbar pull needed that the dozer could deliver - but which the hitch was never designed to withstand!
So it goes with many deeply bogged 4WD's. Few people understand that the limits of recovery points are rated to withstand the maximum drawbar pull of the average 4WD.
If you jerk the snatch strap/wire rope/tow chain, you're doubling the load on the recovery points and the strap/rope/chain.
Add in a BIG 4WD, or something larger (tractor), and you can easily exceed the rated load, of even the best quality aftermarket recovery attachment point.
Cheers - Ron.
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