IMPROVEMENTS IN AN AMERICAN TWO-TONNER.
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TEM number of American chassis on the British market compared with that of only a few years ago is small. It is only those particularly suited to our conditions of service and of outstanding merit which have been able to face the competition of our own producers, but amongst the most successful has always been those produced by Dodge Brothers, and coupled with them are the Graham Brothers vehicles built by the truck division of Dodge Brothers, Ltd. These vehicles have proved to be fast and reliable, and they are used for many arduous services, such as newspaper delivery and the transport of films.
Recently, the Graham Brothers 2tanner has been greatly improved. It now embodies an engine differing in certain respects from the previous design and capable of developing more power, a four-speed gearbox in place of the one previously employed (which gave three speeds only), and four-wheel brakes operated on the Lockheed hydraulic system. The M.D. model has a wheelbase of 11 ft. 5 ins., whilst that of the L.D. model is 13 ft. 6 ins.
As a result of utilizing an extra gear, it has been found possible to raise the axle ratio so that a better performance
1326 on the level can be obtained, whilst, for hill-climbing, slightly more recourse can be had to the gears, although with the more powerful engine this may not be necessary. The final-drive ratio is 5.1 to 1, which is top gear ; third gear is 10.608 to 1; second gear, 20.400 to 1; first, 33.150 to 1; reverse, 38.675 to 1.
The two-piece propeller shaft is, of course, retained, but there is now a parking brake on the transmission, just behind the gearbox. The use of this brake for parking only is emphasized, as it is so powerful that its employment for ordinary service is not recommended. It is of the external-contracting band type with a wide band lined with bonded asbestos. The brake shoes in the wheel drums are totally enclosed, and the drums are of exceptionally large size. The master cylinder of the Lockheed system is of the latest pattern, completely immersed in oil, and any losses are automatically met by oil entering the cylinder, instead of it being necessary to supply it from a separate reservoir on the dash, as was formerly the case.
The frame is straight in the horizontal plane. but curves in towards the front. It is 7 ins, deep at the maximum, has 3-in, flanges and is .-in. thick. Graham Brothers' vehicles are well known for their excellent riding capabilities, and in this latest chassis the rear springs are 4 ft. 6 ins, long and 3 ins, wide, whilst the front springs are 3 ft. 1 in. long and 2 ins. wide ; all are of the standard semi-elliptic pattern and ore rslun g.
A carrier for a spare rim and tyre ie built under the rear of the frame, and a special cross-bearer carries the centre bearing of the propeller shaft.
Reverting to the power unit, this hue L-headed cylinders cast en bloc, with tin detachable heads forming a single cast ing. The cylinders are integral witt the upper half of the crankcase, thin making the construction very rigid Porged from chrome-vanadium steel the crankshaft is machined all over am ground. It runs in five main bearings Light alloy pistons of the Invar-stru pattern are utilized. These permit ex ceptionally small clearances betweet piston and cylinder, so that knocking i: avoided, even when the engine is cold Silchrome steel is used for the exhaus valves. A silent chain drives the timim gear and dynamo, whilst the spindle o the dynamo is extended to carry a fabri. flexible joint through which the drive taken to a centrifugal-type water pump mounted at the rear of the cylinders, so that the cooler water is supplied to the hotter end of the engine.
Lubrication is effected by the combined pump and splash system ; a feature is that if the filter becomes clogged the pump can draw oil from the sump through a by-pass.
The electrical gear is all of North East make, and the distributor is mounted above the cylinders. A separate starter is mounted in the flywheel housing.
Cooling is assisted by a large-diameter Fan driven by a V belt which is adjusted by swinging the fan bracket.
Carburation is improved by embodyng a hot-spot -arrangement, the inlet !onnection being bolted to the exhaust nanifold. Petrol is supplied through an kutortte.
On the footboard is a special greaser or the withdrawal race of the single)late clutch. A small Hyatt roller bear-, ng is provided for the clutch-shaft ;pigot.
All the gears and shafts in the gearox are are made from forgings of chrome7anadium steel ; alloy steel is, of course, ilso employed for the spiral bevels of
he final drive. Incidentally, the rear axle has a vertical banjo casing with a thoroughly well webbed steel casting carrying the gearing. Timken bearings are utilized for the differential, rearaxle shafts and front wheels.
Steering is effected by a Ross cam and lever gear, the axle being of the reversed Elliott type with the tradk rod behind. All steering connections, shackles, etc., are lubricated on the grease-gun system.
The turning circle has a 30-ft. 6-in. radius to the left and a 27-ft. 6-in. radius to the right. Single pneumatic tyres of 32-in. by 6-in, dimensions on Firestone detachable rims are fitted all round.
A point in connection with the frontwheel braking is that the whole wheel assembly can be bolted complete on to the axle, thus making for easy maintenance. In the Lockheed braking system all the piping is covered with braided material to prevent vibration and its evil results. Only one connection goes to the rear axle, the tube there being branched to the sides and protected by a light channel-steel cover.
The standard position for the petrol tank is under the driver's seat. It is rectangular and has a capacity of 12 gallons.
The maximum load to be imposed upon the chassis, including the weight of the body, is 5,680 lb.
The appearance of the chassis is enhanced by domed, pressed-steel front wings and running boards of the same material.
The equipment includes a tyre pump driven from the constant-mesh wheel of the layshaft, and a foot-brake-operated stop light.
It may be interesting. to refer to the care taken in producing a reliable vehicle. At the factory the main bearings are all reamered out in line in-the crankcase. A hardened steel ball is drawn through every bearing ; this closes in the grain and gives a hard skin to the white metal. The cylinder walls are honed, not ground, and very close fitting of the pistons is demanded ; the standard clearance is .0025 in., and the tolerances are .002 in. minimum and .003 in. maximum. Great use of drop forgings is made throughout the chassis, these replacing steel castings wherever possible.
At the works of Dodge Brothers (Britain), Ltd., at North Acton, London, N.W.10,-every engine is run on the bench under its own power for two hours, during which time everything is checked.