THEORY OF OPERATION
1. The purpose of this work package is to provide a general description of the 7 1/2 Ton Crane and an overall
view of its components and their functions.
2. This section explains how the systems and components of the crane work together. A functional description
is provided for each major component and system.
1. The 7 1/2 Ton Crane is a self-contained vehicle, featuring 7.5 ton maximum lifting capacity, optional four-
wheel drive, outriggers for added stability during lifting operations, and three different steering modes: front
wheel steering for normal driving, crab steering for diagonal moves, and four-wheel steering for minimum-
2. Power originates from an in-line, four-cylinder, diesel engine mounted at the rear of the vehicle. The
transmission is mounted directly on the engine and is used to turn driveshafts and to power the tandem
hydraulic pump. One-half of the tandem hydraulic pump supplies hydraulic pressure to winch, and other half
supplies hydraulic pressure to actuate the boom telescope cylinder, boom hoist cylinder, boom swing motor,
outrigger cylinders, axle lockout cylinders, and steering controls. It also provides hydraulic assistance for
The boom is a two-section telescope-type with rotating boom support. Two large-diameter, double-acting hydraulic
cylinders telescope and hoist the boom assembly. A hydraulic swing motor and worm gear rotates the upperstructure.
The cable and hook block assembly are operated by hydraulic winch. Hydraulic and electrical systems on the
upperstructure are connected to the rest of the vehicle by a hydraulic rotary manifold and electrical collector ring.
1. The transmission is capable of four-speed shifting in both forward and reverse. Direction and speed are
selected through hydraulically actuated multiple-disc clutches. The clutches are power absorbing, allowing
shifts under full engine power in both forward and reverse. The clutches are hydraulically controlled and
spring released. Hydraulic control makes the clutches self-adjusting. Each clutch is made of friction plates
and polished-steel reaction plates.
2. The transmission receives power from the engine through the torque converter. The torque converter is fluid
driven, creating a smooth and shock-free drive. Fluid drive also eliminates engine stalling and lugging when
vehicle has a heavy load. With light loads, the torque converter can transmit engine power directly to the
transmission at most engine speeds with no torque multiplication. This provides variable and automatic
speed ratios, reducing need for shifting gears.