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Exhibited at the Scottish Show in November 1934, the Trusty forward-control four-wheeler was rated for a 7.5 ton to 8 ton load (7,620kg to 8,128kg) and was offered in diesel and petrol versions. The diesel Trusty was powered by the 5,261cc DC4 rated at 65bhp@2,200rpm, while the petrol version had the 5,173cc overhead-valve AC4 giving 76bhp@2,400rpm. Both engines were four-cylinder units. In line with engines used, vehicle designations were PE/AC4 and PE/DC4. Engine and four-speed gearbox formed a single unit mounted at three points on rubber. Mountings comprised a central front mounting and two mounting feet bolted to the bell-housing. Power was transmitted through a two-piece open propeller shaft to an overhead worm type rear axle with fully floating shafts.

The Trusty tractive unit was available with six-cylinder diesel or petrol engines.

Both Trusty models introduced in 1934 were continued into 1935 and, later that year, were supplemented with six-cylinder options, with diesel (DC6) and petrol (AC6) alternatives, PE/DC6 and PE/AC6, respectively. The ‘sixes’ could be identified externally by their short bonnets, needed to house the extra length of the longer engines. The 65bhp DC4 engine of the four-cylinder diesel option was replaced by the 85bhp DC4/1. As a portent of things to come for 1936, a long-wheelbase Trusty was shown in November 1935 at the Commercial Motor Show, Olympia, London. This vehicle was built for Thomas Allen Ltd, with a six-cylinder AC6 petrol engine and a load rating of 7 tons to 7.5 tons (7,112kg to 7,620kg).

A Trusty PE/DC4/1 forward-control chassis with a four-cylinder DC4/1 diesel engine.

For the 1936 model year, the Trusty range was expanded from four options to eight, as a result of offering long-wheelbase versions of the four models listed for the previous year, still all PE forward control models. Petrol engines comprised the AC4 and AC6, while diesel DC4/1 and DC6 engines were also offered. Six of the eight vehicles were listed as 8 tonners (8,128kg), but the normal and long wheelbase six-cylinder diesel versions were rated at 6.75 ton to 7 ton capacity (6,858kg to 7,112kg).

Thornycroft entered 1937 with a greatly expanded, not to say bewildering, range of Trusty options beyond the not inconsiderable eight variants offered the previous year, with 24 options for 1937. The eight forward control control vehicles (PE) of the previous year were carried over to 1937 and supplemented by corresponding normal control versions (OE). In addition, four six-cylinder heavy duty UD forward-control models were introduced in normal and long wheelbase forms, with diesel and petrol options powered by 125bhp DC6/1 and 104bhp AC6 six-cylinder engines, respectively. Four normal-control PD models corresponding to the forward control UD models were also introduced. Load capacities in the range varied from 6.25 tons to 7.75 tons (6,350kg to 7,874kg), depending on version. Then, in July, came the Trusty four-wheel six-cylinder tractive unit with petrol (UD/AC6/1) and diesel (UD/DC6/1) options, suitable for articulated outfits with a 13 ton payload (13,208kg).

This forward-control six-cylinder Trusty PE/DC6 was used by a well-known brewer.

Careful study of the progression of the Trusty range from the two lorry options initially offered in 1934 to the 24 listed in 1937, shows that the range developed along logical lines. However, Thornycroft pruned the range down to 16 options for 1938, dropping the UD and PD heavy duty four wheelers. However, both UD tractive units were retained. This range remained the same for 1939, except that the diesel version of the UD tractive unit was dropped, leaving the petrol-powered UD/AC6/1 as the only Sturdy tractive unit. All four-wheelers were rated at 6.5 tons to 8 tons (6,604kg to 8,128kg).

In 1936 The Commercial Motor journal carried out a road test of a normal-wheelbase 8 tonner (8,128kg) powered by a four-cylinder DC4/1 diesel engine. A Williams and James engine-driven exhauster (i.e. vacuum pump) powered the brake servo system, in the absence of the required level of vaccum in a diesel inlet manifold. Recorded figures included acceleration of 0 to 30mph (48.3kph) in 45 seconds and, running on Shell Diesoleum, fuel consumption was 13.64mpg (20.3 litres/100km) on a 26 mile (41.8km) out-and-return course, over undulating main roads at an average speed of 20mph (32.2kph). A strong headwind was encountered on the outward run. Stopping distance from 30mph (48.3kph) was 50ft (15.2m), which was considered good for the vehicle class, and was claimed as evidence of the futility of the prevailing 20mph (32.2kph) speed limit for vehicles weighing over 2½ tons (2,540kg) unloaded. Test staff reported no sign of exhaust smoke, considered important for other road users; global warming was not the issue in 1936! Cab noise was described as medium in comparison with other vehicles.

A normal control Trusty PE/DC6 powered by a six-cylinder DC6 diesel engine.

DC diesel engine comments: introduced in 1934, Thornycroft’s 5,261cc DC4 diesel engine was a four-cylinder unit with indirect injection giving 65bhp@2,200rpm. The firm introduced an uprated version in 1935, the DC4/1 rated at 85bhp, an increase of no less than 31 per cent over its predecessor of the same capacity. This power increase was all the more impressive for being achieved without rpm increase. Modifications included the Ricardo arrangement of indirect injection. A six-cylinder DC6 version of the DC4 was introduced in 1936 displacing 7,892cc and giving 99bhp. In due course, this engine was redesignated DC6/1, after uprating to 125bhp@2,200rpm with the Ricardo system of indirect injection applied to its smaller DC4/1 brother.


“Trusty” Class 6½/7½ ton (6,604/7,620kg) chassis, oil-engined types “PE/DC4/1” & “PE/DC4/1 long”

December 1936


  • Four-cylinder type DC4/1 watercooled diesel
  • Bore 4.125ins (104.8mm)
  • Stroke 6ins (152.4mm)
  • Swept volume 5,261cc
  • Maximum BHP 85@2,200rpm

Monobloc construction, assisting rigidity of engine. The cylinder head is easily detachable for decarbonising and grinding-in the valves. Renewable wet cylinder liners, aluminium alloy pistons, overhead valves and detachable exhaust valve seats are fitted.

Valve Gear
Operated by push rods and adjustable rockers.

Dynamically and statically balanced and carried in five white-metal lined bearings of large diameter.

Forced feed system from a rotary gear pump, delivering oil to the main and connecting rod bearings, also to the camshaft bearings and overhead valve gear. Before returning to the sump, which has a capacity of 3½ gallons (15.9 litres), the oil passes through a large metal strainer.

C.A.V.-Bosch injection pump governed at maximum and idling speeds.

Cooling System
By centrifugal pump and belt-driven fan mounted on the front of the cylinder block. The tension of the belt is adjustable. The radiator is rubber mounted.


Single plate dry type with a particularly smooth action when taking up the drive.

Unit with engine and clutch and providing four forward speeds and a reverse speed. The gear shafts are carried on ball and roller bearings. The change speed lever is on the driver’s left hand.













Propeller Shaft
Open, tubular type with universal couplings and intermediate bearing.


I-section axle body, forged in one piece. The king pins are supported on taper roller bearings. The track rod is adjustable.

Of the full floating type with a drop forged casing and overhead worm gear. The worm gear and differential can be withdrawn without removing the road wheels. Both the worm shaft and differential are carried on ball bearings and the road wheels on taper roller bearings. Final drive ratio is 8.25.

Made of alloy steel to ensure easy riding and secured to the axles by our patented type of relieving plate (Patent No. 199,522), which relieves the holding-down bolts of stresses due to flexing of the springs.

The spring dimensions are:

  • Front springs, 3ins (76.2mm) wide, 4ft 0ins (1.22m) centres.
  • Rear springs, 4ins (101.6mm) wide, 5ft 0ins (1.52m) centres.


Operates on all four wheels through triple vacuum-servo cylinders. One pair of internal expanding shoes operates in each brake drum. Front brake shoes are 3ins (76.2cm) wide and rear brake shoes 6ins (152.4cm) wide. The diameter of the front and rear brake drums is 17ins (43.2cm). The brake drums are removable without disturbing the hub bearings.

Employs the same set of shoes in the rear drums as the foot brake through an independent means of operation without vacuum servo assistance.

This is of the cam and roller type providing easy control for the driver. The turning circle is approximately 50ft (15.2m). (Long wheelbase chassis, 60ft/18.3m).

The frame is of pressed steel with substantial crossmembers giving an extremely rigid construction without employing excessive weight. The maximum frame depth is 9½ins (24.1cm)

Fuel Tank
A 30-gallon (136.4 litres) steel tank is carried on the nearside of the chassis frame. A vacuum tank draws the fuel from the main tank and delivers it by gravity to the injection pump.

Wheels And Tyres
The standard equipment is 36ins x 8ins (91.4cm x 20.3cm) R.T.A. tyres, single front, twins rear, fitted to detachable pressed steel disc wheels. All the wheels are interchangeable. The standard position for carrying the spare wheel and tyre is between the frame members at the rear.


Taxation Class £70.

Weight of Chassis
With 36ins x 8ins (91.4cm x 20.3cm) R.T.A. tyres, spare wheel carrier, battery, standard lamps and dynamo, oil in engine, gearbox and rear axle, but excluding fuel, water, spare wheel and tool kit 3 tons 8cwt 2qrs (7,672lbs/3,480kg)

  • Standard body allowance - 15cwt 0qr (1,680lbs/762kg)
  • Weight of chassis with body allowance - 4 tons 3cwt 2qrs (9,352lbs/4,242kg)
  • Ditto “Long” chassis 4 tons 5cwt 0qr (9,520lbs/4,318kg)

12 volt, 5 amp electric lighting set with head lamps, combined tail and “stop” light, 105 amp-hour battery, 260 watt dynamo, 24 volt axial starter, electric horn, fuel gauge, spare wheel, tyre and carrier, illuminated instrument panel with speedometer and mileage recorder, oil pressure and dynamo charge indicators. Radiator blanking-off sheets, front mudguards, kit of tools including jack, driver’s instruction book and parts list.

Extra Equipment
The following can be supplied at extra charge:

Mechanical Tyre Pump
A mechanical tyre pump driven from the gearbox, with sufficient tubing to reach all tyres.

Power Take-off
Bolted to the chassis gearbox and transmitting up to 6hp or up to 28hp.

  • Driver’s Seat.
  • Mate’s Seat.
  • Non-Skid Chains.
  • Radiator Muff.
  • Trafficators.

Standard Cab Equipment
Includes sliding windows in doors, safety glass windscreen, electric windscreen wiper, driver’s mirror, licence holder, and front and rear number plates.

Forward Control Cab
A special type of lightweight cab has been designed to suit these forward control chassis, and purchasers who desire to make their own arrangements as regards bodywork will find it advantageous to order the Thornycroft cab at the same time as the chassis. However, where the cab is not ordered from us, we wish to make it clear that the chassis is supplied with a full-width dash, engine bonnet, floor boards for driver’s compartment, front mudguards and combined engine compartment rear panel and cab base. Both the head and side lamps are fixed in position and wired up to the instrument panel.


Information for these pages comes from contemporary Thornycroft technical and other data, as well as contemporary copies of The Commercial Motor.


Trusty outline diagram 43kb pdf