Heavy Recovery Wrecker

Overview

A heavy recovery wrecker is a purpose-built truck used to recover, right, and tow large vehicles, such as articulated lorries, buses, and coaches that have broken down, crashed, or overturned. Ordinary tow trucks cannot handle these weights. The wrecker combines several recovery tools on one heavy chassis: an underlift for towing a casualty by its axle, a telescopic recovery boom for lifting and righting, and a multi-drum winch system for dragging vehicles back onto the road. Operators are commercial recovery firms and highway authorities who clear incidents involving heavy vehicles.

The truck is built on a reinforced chassis with a powerful diesel driveline. All recovery functions run from a single hydraulic power system, and outriggers plant the truck firmly so it can lift heavy loads without tipping.

Underlift

The underlift is the everyday towing tool. A telescopic underlift beam extends rearward from under the body, and a cross bar with two adjustable L-arms cradles the casualty vehicle's axle or wheels. Hydraulic underlift cylinders then raise that end of the vehicle clear of the ground so it can be towed on its remaining axles. Because the underlift carries the casualty's weight on a long cantilever, the beam is fabricated from high-strength S960QL plate and the L-arms are forged 42CrMo4. Wheel lift grids support the lifted wheels when towing by the wheels rather than the axle.

Recovery boom

For lifting and righting, the recovery boom provides vertical reach. An inner boom hinges off the body and a telescopic section extends from it, driven by an extension cylinder. Two lift cylinders raise the boom. At the tip, a sheave head carries the winch ropes over rope sheaves. With the boom set up and outriggers down, the wrecker can lift an overturned truck and roll it back onto its wheels.

Winch system

The winch system supplies the pulling force for both dragging and lifting. The main winch uses a high-line-pull hydraulic motor through a planetary reduction to spool 22 mm wire rope off a drum, delivering tens of tonnes of line pull. Two auxiliary drag winches handle separate pulls, for example holding a load steady while the main winch lifts. Snatch blocks double the effective line pull, and forged recovery hooks terminate the ropes.

Hydraulic power

Every recovery function runs on hydraulics. A power take-off drives an axial piston pump of around 90 cc per revolution at 350 bar, drawing oil from a 200 L reservoir. The directional valve bank routes oil to the underlift, boom, winches, and outriggers as the operator selects them. An oil cooler handles the heat of sustained winching, and four-spiral hoses feed the cylinders and motors.

Superstructure and stability

The recovery gear mounts on a welded superstructure with a work deck and equipment lockers for chains, straps, and rigging. Lifting heavy loads on a boom would tip an unsupported truck, so four hydraulic outriggers extend and plant foot pads on the ground to widen the support base. A scene light mast illuminates night-time recoveries.

Materials and load paths

A wrecker concentrates very large forces into a few structural members, so material grade follows the load path. The underlift beam and telescopic boom section use S960QL, the highest-strength structural steel in common use, because they are long, slim, and carry bending loads at full extension. The fixed inner boom and the body subframe use S690QL and S700MC respectively. Components that take direct contact loads, the L-arms, hooks, and cross bar, are forged from 42CrMo4. Pivot pins are induction hardened so the joints survive the grit and water of roadside work.

Variants and capacity

Wreckers are rated by boom lift capacity and by underlift towing capacity, and the two are specified separately because they are used in different recovery situations. A mid-range unit on a 26 t chassis might offer a 25 t boom and a 12 t underlift, while a top-end 8x4 machine pushes the boom past 50 t. Some operators add a rotator, a turntable between the boom and chassis that lets the boom swing to the side for off-road recoveries, and a rear spade or anchor that digs in to resist the reaction of a heavy winch pull.

Driveline, electrical and use

The driveline is a large inline-6 turbo diesel near 13 L with a 6-speed automatic transmission and retarder for descending with a towed load. The electrical system runs at 24 V and drives amber warning equipment: a light bar, roof beacons, and scene work lights managed by the function controller. A dual-circuit air brake system with disc brakes stops the heavy combination. In service the wrecker responds to highway incidents, sets up its outriggers, recovers the casualty with the boom and winches, then tows it away on the underlift.