KNOW T
Page 58
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Watch those brakes
THE specifications laid down in the Motor Vehicle (Construction and Use) Regulations 1972 for brakes on motor vehicles and trailers are extremely complex, and I do not propose to bore readers with the exact details of the requirements but rather to deal with the subject in a general manner.
The Regulations themselves can always be consulted if more detailed information is required.
Every motor vehicle must have either an efficient braking system with two means of operation, or two efficient systems each with its own separate means of operation. A parking brake must be provided to prevent at least two wheels (one if a three-wheeler) revolving when the vehicle is not being driven.
Motor vehicles first used after January 1, 1968, must have a parking brake with a means of operation independent from that operating the primary brake, which maintains the brakes in action by direct mechanical means (eg by rod or cable).
It must also be without the intervention of any hydraulic, electric or pneumatic device, and able to hold the vehicle stationary on a gradient of 1 in 6.25 without the assistance of stored energy. This represents a braking efficiency of 16 per cent.
Rigid four-wheel vehicles, first registered before January 1, 1968, must have a main braking system, usually but not necessarily the footbrake, with an efficiency of at least 45 per cent, and a secondary system with an efficiency of at least 20 per cent.
The secondary system is usually the handbrake. but any other means of operation, including a dual-line split foot brake which still gives 20 per cent braking efficiency when half the system fails, is permissible.
Vehicles first registered after January 1, 1968, must have an efficiency of 50 per cent on one system and 25 per cent on the other. Several special exemptions are made for vintage vehicles and for certain works trucks.
Steam wagons have a pragraph all to themselves in the braking requirements. The engine of these old-timers is deemed to be an efficient braking system, with one means of operation if the engine is capable of being reversed.
On newer wagons, ie those registered on or after January 1, 1927, this concession applies only if the engine "is incapable of being disconnected from any driving wheels of the vehicle, except by the sustained effort of the driver."
Regulation 55 deals with tyres for heavy motor cars, and lays down as a general rule that pneumatic tyres must be used.
Exceptions are made for vehicles first used before January 2, 1933: vehicles exceeding 4,070kg (4 tons) unladen weight, mainly used on rough ground. vehicles used for street cleansing, collection or disposal of refuse, or for the collection or disposal of the contents of gullies or cesspools.
All these vehicles may be fitted with solid rubber tyres. Turntable fire escapes, tower wagons and works trucks may also be fitted with solid tyres.
Regulation 56 says all heavy motor cars must be fitted with wings or other similar fittings in order to catch so far as is practicable, mud or water thrown up by the wheels, unless adequate protection is afforded by the bodywork of the vehicle.
Exemptions are made for the rear wheels of artics employed in carrying round timber, works trucks and unfinished vehicles travelling to works for completion.
Whether -adequate protection is afforded by the bodywork" is a question of fact — the fitting of mud-flaps could provide the necessary extra protection to comply with the law. The law concerning wings for motor cars is identical with that just described for heavy motor cars.
Regulation 56 is the last section in the regulations which deal specifically with heavy motor cars.
Regulations 68 to 73 deal with trailers, and the first of these regulations lays down their overall length as 7 metres (a fraction short of 23ft). If the following conditions are observed this length limit is extended to 12 metres (39ft 41/2in): (a) The trailer has not less than four wheels and the .distance between the foremost and rearmost wheels is not less than three-fifths of the overall length; and (b) It is drawn by a motor vehicle having an unladen weight of 2,030 kg or more (2 tons).
The restriction on length does not apply to a trailer used for the conveyance of indivisible loads of exceptional length; to land implements; to trailers forming part of an artic; to a broken down vehicle being towed in consequence of the breakdown; to a trailer which is a trolley vehicle in the course of
construction or delivery or to certain trailers which are machines used in connection with tar macadam road making or repair. The exemption for semi-trailers does not mean that an artic can be of any length because Regulation 9 limits the total weight of an articulated vehicle to 15 metres (49ft 21/2in). In calculating the length of any trailer the drawbar and drawbar fittings may be excluded.
Section 69 states that provided a trailer is fitted with pneumatic tyres it can be up to 2.5 metres (8ft 2in) wide on condition that the drawing unit is a locomotive, motor tractor or heavy motor car also fitted with pneumatics, and that the trailer edge does not extend more than 305mm (12in) outwards beyond the edge of the tractive unit.
Trailers not complying with the foregoing conditions are limited to 2.3m (7ft 6in) width. This width may be exceeded by 380mm (15in) in the case of a trailer used by a travelling showman before January 15, 1941, and by 150mm (6in) on trailers manufactured before January 1, 1933, and which have been converted from solid to pneumatic tyres and whose width exceeds 7ft 6in because of the conversion. The width of 2.5m is permitted for semitrailers forming part of an artic, the motive unit of which is a motor car exceeding 2 tom unladen weight.
With some minor exceptions pneumatic tyres are required or trailers. The rear wheels, or ir the case of a two-wheeled trailel both the wheels must be fittec with wings. Exceptions to thi: rule are made for trailers in ar unfinished condition travellinc to a works for completion; lanc implements and theil conveyors; living vans; wate carts; railers used for carryinc round timber; fire brigade traile pumps; broken down vehicle and vehicles limited to 12mpl or less.
Trailer brakes are dealt witf in Regulations 70 and 71 and will deal with these in my nex article.