Here I've used my original "pick-up truck" as the basis for a tow truck with pneumatic towing boom. The original model is otherwise almost unchanged, apart from obvious changes to the rear cargo bed, plus modifications to the suspension to carry the extra weight.
Truck has full suspension, rear wheel drive, 4 cylinder engine, 3-speed gearbox, and Pitman-type steering.
About this creation
Both pneumatic spring pumps, posing as exhaust towers, are plumbed in and fully functional. The boom can be controlled using either, or both, of the pumps.
Close up of left hand side boom controls - pneumatic valve deploys tow bar, lever to left is ratchet release for main crane hook.
White object at bottom right is boom brace in stowed position.
Right hand boom controls. Main crane hook is operated by a rubber wheel from a Lego Space lunar module.
Loading the broken-down vehicle
With boom braces in place - pneumatic pistons are strong enough for light cars like the 8860, but might not be for other vehicles - so this truck has a set of braces it can apply to the boom to provide additional support for very heavy loads. Boom braces fold forward and lie fat on the truck bed behind the pneumatic rams when not in use.
Boom is set up to allow unimpeded use of crane hook whether axle jack is raised or lowered; hook operates in gap between left and right side of jack.
Also visible here are the yellow rear springs to firm up the rear suspension.
Front suspension has been augmented by two yellow springs, whilst the central long grey spring has been eliminated, and the long grey springs to each side have been replaced with long black springs. The result is a much more satisfactory smooth operation of the front suspension.
Newly-added front winch is kept in check by the ratchet at top centre of this shot. Lever at top right is ratchet release, crank just below it is crank for winding in the winch.
Quoting Nick Barrett
Effective looking system, pneumatics can bear more weight than they're sometimes given credit for. A compressor solves many problems...
Cheers Nick. I'd certainly trust pneumatics over many of the alternative lifting systems used in models of the 80s like the wheeled front end loader 8853 and the front bucket of the 8862 JCB (the latter of which was particularly weak), but the rack and pinion lift used in the main body of the bulldozer 856 did a jolly good job with the gearing not overloading any given component - there was more risk of the chassis popping open (due to lack of proper bracing behind the "radiator") than the mechanism snapping!