Road and workshop
Page 45
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by Handyman
Vehicle recovery: tricks, trucks and tactics (24)
• As a final item to this series on vehicle recovery, it is fitting that we should have a look at our main tool, the recovery unit itself. Throughout road transport history, few firms except certain garages have ever bought a completely brand new wrecker or salvage unit. Every eight years or so, one can see a nice, shiny crane-cum-workshop job standing on the forecoUrts, although a closer look would invariably find the actual chassis to be somewhat longer in the tooth than its new body.
Up to the last war, a haulier's recovery vehicle was usually a tough old goods vehicle that was outdated for general freight, written down to E1 on the books but considered fit for the task of bringing in the cripples. These units almost always had their tails "bobbed off" right up to the rearmost spring hanger, together with the heaviest springs and tyres they would take. Invariably the jibs and tackle would be by Harvey-Frost and most often manual, although where a pto could be fitted, an additional hauling drum and cable would be added.
These old units did yeoman service, and at this moment I still possess a 33-year-old Harvey-Frost twin-block crane unit that is now on its fifth chassis, and as reliable as ever, needing only a cable change as per insurance inspection. This is now mounted on a fourwheeled, air-braked chassis. With the advent of the artic, the main need in most cases is to lift the front end of a motive unit, and so this size of crane is coming back into popularity for general tow and carry work, although there wilk always be a need for the really big job to de-ditch. However, ex-War Department tackle came on the market, and a variety of British and American fourand six
wheeled wreckers are still around, although the lifting and hauling powers claimed by some advertisers are somewhat ambiguous. A check on their tyre size and cable section makes one feel inclined to erase one or two Os from their suggested capacities! Make no mistake about this, size and gross weight is most useful, but the true measure of capacity is still determined by the wires, blocks and gears that have laid-down limits, and when an experienced firm such as Harvey-Frost says 8or 10-ton capacity, this is it—they know what they're talking about.
However, as the WD equipment begins to fade out—and this is already happening—general haulage people will again make up their own wreckers from sound, used chassis, because this is still the most economical approach. Where consideration is being given to producing a recovery vehicle from this source, there are certain important points to aim for. I spoke of "bobbed" off tail ends and this is important, as the actual load bearing point is the hook, and since this has to be rearwards of the rear axle centre, the distance or overhang between rear axle centre and a line dropped from the hook is critical in relation to both the distance between front and rear axle centres, and the weight forward of the rear axle. Thus, if the weight forward of the rear axle is, or is almost cancelled out by the overhang and the load on the hook, the vehicle will tip or be far too light on the steering.
So, if a home-brewed recovery unit is to be used to the limit of its lifting tackle, it is important to establish the weight forward of the rear axle, and this weight must be safely in excess of the combination of top working load on the hook, and the effect of leverage exerted by overhang.
Shortening the overhang has the same effect as front-end ballast, therefore for those considering a "brew-up unit" to their own particular liking. I suggest that they first study the simple formula shown left. This is prepared by Harvey-Frost for the guidance of home-builders of mobile cranes, wreckers, etc., and there is no safer yardstick.
One final word: the efficiency and effectiveness of any salvage unit still rests in the hands of its operator—he can make or mar its true usefulness. Therefore when choosing your chassis and the tackle to suit your purpose, do this with care, and never hesitate to consult the experts, they are always glad to help. Above all select with equal care the man who really matters and who can make it all worthwhile—your recovery operator.