The bodies and underframes were built as an integral structure, the complete body and underframe being capable of carrying all the superimposed loads normally encountered in service and a 200% overload. The main body pillars were of a 16 s.w.g. thick mild steel pressed top-hat section, with the flanges located against the outer skin to form hollow box sections. These were connected by light and waist rails together with intermediate 16 s.w.g plate of angle and "z" section, and the 1/8 in plate cantrail. The main carlines were of similar section and thickness as the pillars, and were tied together by purlins of shallower top-hat section.
The body side, end and roof panelling was 16 s.w.g. steel, and these were stitch welded to the body framing in cast iron jigs to minimise distortion and buckling of panels. All joints between adjacent body side and end panels were welded and ground smooth after assembly to provide a completely flat exterior. The underframes were a conventional design of mild steel rolled sections and plates, with members spaced to accommodate the power and transmission equipment, and fabricated by electric welding. Standard BR drawgear and light alloy Oleo hydraulic self-contained side buffers were fitted, although some were fitted with spring buffers mounted on adapter brackets until receiving the one piece Oleos during overhaul in the late '70s.
The standard BR swing bolster bogies were used, and were fitted with Timken roller-bearing axleboxes and lateral control bolster dampers. 22 inch vacuum cylinders were carried in the power car bogies, although they were later changed to the standard 21" rolling ring type. Trailer cars had 18" cylinders and one bogie and carried a dynamo. On the power cars these were driven by V-belts from the transmission. Brakes were the Gresham & Craven quick release vacuum type, with two Clayton exhausters also driven from the transmission by v-belts. There were brake valves in the guards van, and in each cab, the cabs also containing the handbrakes. The TBS vehicles had a vertically mounted hand brake wheel by the corridor connection door but these was later removed.
BUT supplied their standard engine and transmission equipment, with each Leyland 680 engine driving a final drive on the inner axle of the nearest axle via a freewheel, four speed epicyclic gearbox, and cardan shafts. An air compressor was mounted on each engine to supply air for the electro-pneumatic controls. Radiators, mounted on the side of the frames were cooled by fans driven by a right angle drive on the engine. Each exhaust system had two silencers to cut down on noise.
Horsepower per ton of tare for a 3-car set (86 tons) was approx 7.0, and fully laden would be about 6.0hp per ton.
For heat and noise insulation cars were sprayed with asbestos, 1/4 inch thick on the inside of the side, end and roof sheeting, and 3/8 inch thick on the underside of the aluminium dovetail floor sheets. These were covered with 1 3/16 inch thick cork, to give better protection against noise, onto which the linoleum was laid.
J Stone & Co (Deptford) Ltd provided the lighting equipment, with 60W 24V lamps in the saloons powered by 150 amp Tonum generators. Standard BR A2 type lead acid batteries were used which had a capacity of 440 amp/hour. Destination and route indicator boxes could also be illuminated.