The Big J4 Series covered a gross vehicle weight range of 16 to 32 tons, for rigid, drawbar and articulated use.

They were well suited for use as skip loaders, lutons, horse boxes, drop-siders, and tippers and included heavy duty suspension with long semi-elliptic springs, big and powerful brakes and a load sensing device on tractor models to ensure controlled progressive braking by matching braking effort to road and load conditions. This minimised the risk of jack-knifing.

The standard petrol tank had a capacity of 46 gallons, but a larger 63 gallon tank, or two dual 46 gallon tanks were available for long distance use.

The cab featured wide doors with a grab handle and a step at a convenient height for easy access. Routine maintenance was made easy because the engine cover was quickly removable, and oil and water levels could be checked within the cab. Grease points were easily accessible and kept to a minimum.

The Big J4 was available as a four-wheeler, load carrier and tipper.

The Big J4 had a V6 diesel which produced 170bbhp at 2,600rpm or an AV 505 (right hand only) engine which produced 170bhp at 2,400rpm or the AV,471 (right hand only) which produced 150bhp at 2,400rpm. The clutch was a single plate, cushioned drive unit linked to a five-speed constant mesh gearbox.

The suspension consisted of semi-elliptic springs. They were 54" long by 4" wide at the front and 58" long by 3½" wide at the rear. Telescopic shock absorbers were available on front axle only. The frame was made of high tensile alloy steel side members. It has pressed steel cross members. Cross members and spring brackets attached to frame side members by high tensile bolts. Frame width 34" international standard.

There was a 24 volt insulated return system of wiring. 35 amp alternator fitted as standard. A circular tank of 46 gallons capacity was fitted. The cab was of all steel welded construction with a forward entrance, and one piece screen with a generous area giving good visibility. A shock absorber type driver and passenger seat, available as optional extra. A sleeper cab was also available on export models.

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