The Motor YEAR BOOK, 1954     BRITISH CARS OF 1953
BRISTOL 403

Externally, the difference between the Bristol 403 saloon and the preceding Type 401 is confined to small items of decoration. Mechanically, a number of changes have been made having an important effect upon the performance, road holding and habitability, so much so that this model comes on the border line between modified and an entirely new type.
It is, however, treated as a modified concept on account of there being no change in basic dimensions. This notwithstanding, engine output has been increased by over 17 per cent. by raising the peak r.p.m. to 5,250, at which speed 100 b.h.p. is realized whereas the peak of the 401 was found at 4,500 r.p.m. where it developed 85 b.h.p. This has followed a redesign of the cylinder head, bringing larger inlet valves-a change it is claimed which does not impair either flexibility or fuel consumption. To cope with the increased bearing loads at the higher speeds the crankshaft is counter-weighted and runs in larger main bearings of the copper-lead strip type. The sump has been enlarged to carry 1½ gallons of oil and the oil pump has a greater capacity so as to circulate the oil more frequently and at higher pressure. The mechanism of the gearbox is unchanged but the propeller shaft now has "Layrub" universal joints which cushion the drive at low speeds. An important change has been effected in the suspension system by the provision of an anti-roll bar connecting the front wheels. The strength of this bar has been calculated to provide a reasonable but not excessive degree of understeer - an important point in a light car of moderate dimensions which may at times be called upon to carry a heavy load of luggage placed behind the rear axle centres. The twin facts that a heavy load can be carried by the car, and that the low wind resistance results in little retarding effect at high speeds, has made close study of the braking system imperative. Pedal pressures have been reduced by increasing the mechanical advantage of the driver's shoe over the brake shoe and the danger of fade has been made remote by the use of finned light alloy drums into which the cast iron liner is bonded by the Al-fin process. The interior of the car has not been changed, but modifications have been made to the ventillation system. Air enters from just in front of the radiator and after passing through heat exchangers enters the body at floor level on both sides. By moving a control, air from the upper half of one of the heater elements can, by an electric fan, be blown either up to the windscreen or down to the driver's feet. Moreover, to meet conditions when the ambient temperature is very low or the speed of the car insufficient to supply enough warm air, it is possible to close the ducts and recirculate warmed air to the windscreen and the feet. Minor changes of real worth are improved venting which permits the 17-gallon fuel tank to be filled rapidly, easier access to the trickle charger which is included as standard equipment, and adjustment to the rack and pinion steering gear.

BRISTOL 404

The basis of the new Bristol is an extremely rigid box-section frame in 14-gauge steel, similar to that of the 403 but 18 in. shorter, giving a wheelbase of only a fraction over 8 ft. Tapering sharply from about the mid-point to the front, the frame has side members 6¼ in. deep, and measures 47 in. across at the widest point. The box section is continued for the front and rear cross-members, with extra rigidity provided in the centre by a 3-in. diameter steel tube, which incidentally carries the rear extension of the combined engine, clutch, and gearbox assembly.
From the widest point the side of the frame is continued rearwards, in drilled girders of smaller section, sweeping upwards over the rear axle as in the 403, but instead of extending behind the axle, it is carried vertically upwards immediately above the "arch" to provide an anchorage for the very large telescopic shock absorbers. The whole chassis is further strengthened by an integral floor, welded to the frame.
This emphasis of stiffness, which is, of course, helped by the reduced length of the chassis, is necessary because the 404 Bristol, unlike most saloon cars, and the Type 403 in particular, does not derive any of its strength from the body. Whereas the fourseater saloon is built up on a complex arrangement of small diameter tubes with boxsection steel side pillars, the new car is panelled in 18-gauge light alloy on a body frame of wood while the wide and very light doors have alloy frames. In this way the dry weight has been kept down to 20½ cwt., which promises an excellent performance with either the standard engine, developing 105 b.h.p., or the alternative 125 b.h.p. sports engine.
As with all Bristols, the body design shows many traces of aircraft influence, being developed largely in the wind tunnel at Filton, and despite the full-width style, the frontal area is small.
The suspension differs only in detail from the previous arrangement. At the front a built-up bracket at each corner of the frame carries a single, slightly inclined and slightly trailing wishbone, between the arms of which passes the telescopic damper, hinged at the bottom to the outer end of the single transverse leaf spring. This has more leaves than on the larger car, but is actually rather softer because of the reduced weight. An orthodox torsion anti-roll bar is carried in rubber bushes below the chassis frame, and the spring and all joints are protected by water-resisting gaiters.
As before, the rear suspension is by longitudinal torsion bars running forward to an anchorage in the tubular cross member, and the axle is located by these and by a triangular stabilizing bracket mounted on top of the differential casing. All the friction surfaces in the rear suspension are lubricated automatically from the rear axle, while the remainder of the chassis has a one-shot system worked by a pedal on the toe-board.
Considerations of space under the low bonnet have led to the unusual forward-tilting attitude of the radiator which, like the engine, is rubber mounted and actually gives slightly better cooling than it would in a vertical position.
A modified Borg and Beck 8-in. single dry plate clutch transmits power to the Bristol four-speed gearbox, which is fitted with an exceptionally smooth and positive remote control change. An extension behind the gearbox which forms one of the engine mountings also makes possible a very short propeller shaft, fully balanced and provided with Layrub universals to cushion the drive.
To cope with the very high speeds which should be obtainable not only on long open roads but under ordinary give-and-take conditions, special attention has been given to heat dispersal and long life from the brakes. A new design of "Al-fin" drum is fitted at the front, with a bonded, cast-iron liner and a single large cooling fin which is dished to the shape of the pierced disc wheel. The front drums measure 12 in. by 2¼ in. and the brakes are of the two-leading shoe type, with automatic adjusters to take up wear. Single-leading shoe brakes operate in 11 in. by 1¾ in. Al-fin drums on the back wheels, and all linings are of anti-face material, ¼-in. thick. A Lockheed tandem master cylinder is now used, so that there are two balanced but independent braking systems, on front and rear brakes. A pull-up handbrake between the seats works on the back wheels only.
The steering is of the usual Bristol rack and pinion type, and so arranged that the car can easily be produced with either right- or left-hand drive.
The thickness of the doors is used for two large pockets, and there is a lockable glove box in the facia on the driver's side, but the major space for luggage is on a platform under the very large rear window. When only two passengers are carried, this space can be considerably enlarged by folding down the back of the occasional seats.
The light alloy fuel tank is mounted below this platform, behind the rear axle, and has a central filler with a cap released from inside the car. There is no other opening at the rear, for the spare wheel has been ingeniously fitted in the near side wing; just behind the front wheel arch, and is reached by swinging the whole of this panel, below the chromium rubbing strip, out and upwards to a vertical position. On the offside a similar weatherproof compartment encloses the 51-amp.-hr. battery.
The Motor Year Book 1954