SOUND CONTROL

R H Johnston

The A30/35 was never a quiet car by modern standards though it was not unduly noisy for a small car of the period. Those who have become accustomed to more modern transport may consider that it is worthwhile trying to make their cars quieter.

Primary Sound Control

The first step to a quiet car is to ensure that there is as little noise generated by the mechanical components as possible. A car in poor mechanical condition is difficult to quieten using sound deadening materials alone. So let us consider the main sources of excessive noise.

The Engine If the engine is in good condition then there should only be a small amount of valve train noise, and little else at tickover. Except for timing chain rattle, which is most prominent at tickover, the noise from excessive clearances tends to become louder as the engine speeds up. Excessive tappet clearances, other valve train wear, worn bearings, loose fitting pistons or a slack timing chain all contribute to engine noise. Poor engine mountings can cause extra vibration. Apart from these aspects of primary maintenance, there is little that can be done to make the engine itself inherently quieter. There is however one ancillary which produces a lot of noise at high engine speeds. This is the fan. To get an idea of just how much noise is produced, remove the fanbelt and run the engine briefly. The engine runs very much more quietly than normal at high speeds. This is how much of the quietness of modern car engines is often achieved. For optimum quietness, fit an electric fan controlled by the water temperature. This also helps to keep the engine at the optimum temperature. Alternatively, some more modern engine driven fans produce less noise as they are better designed, and are driven at a lower rotational speed using a larger pulley. Fan noise depends very much on the speed of the tips of the fan, so reducing the rotational speed makes the fan quieter, but it then has to be designed to pass more air to compensate for the reduced speed. A Marina fan, together with its larger pulley may be suitable, but may need spacing out: it is not suitable for 1275 engines with the oil separator on the timing cover because there is insufficient space between the engine and the radiator.

Gearbox A rushing noise usually arises from worn bearings, but the worst noises are caused by broken teeth, especially in first and reverse gear.

Rear axle The rear axles were never quiet even on new cars, as testified by contemporary road tests, a whine being common. Additives such as Wynn's can help here, but growling probably means a need for a replacement unit.

Propshaft This component can give heavy vibration if it is bent or the universal joints are worn. No amount of sound deadening will cure this!

Steering and Suspension Knocks when travelling over bumps are caused by looseness, sometimes within components, sometimes because the bolts are loose. Shockabsorbers, particularly the rear ones are prone to this problem. Exceptionally, wheel bearings can become noisy, but this does not seem to be too common a problem on this type of car. The rubber bushes in the front suspension can eventually become soft and allow excessive looseness and should be replaced if this occurs. On the rear suspension, early cars had only a thin fibre pad between the axle and the spring, later ones have rubber pads, which are more effective at keeping the road and axle noises out of the car.

Squeaks and rattles Loose components on the bodywork, including pipes and cables can cause squeaks and rattles, and sometimes resonant noises too, and can be difficult to find. I once had an irritating 'zzz' which eventually turned out to be the petrol pipe vibrating against the bodywork just in front of the radiator. Rattling doors and windows not only cause this noise, but normally then contribute to wind noise and draughts.

Secondary Noise Control

Secondary noise control is what we usually think of when we start to try to make a car quieter. There are two main areas of attack: prevention of noise reaching the car interior, and absorbing what has arrived in the car once it is there.

Keeping noise out Ensure that all the rubber grommets are fitted correctly between the engine and passenger compartments, as sound travels much more easily where there is no barrier. For the same reason ensure that there are no holes in the heater air tubing. Engine noise is also reduced substantially by lining the bonnet with thick, soft woollen felt. I glue it in place with copydex. (NB The material must be a type which is reluctant to burn, hence a woollen material must be used.) A further layer of felt is placed on the passenger compartment side of the panel through which the pedals come, but make sure that pedal travel is not reduced as a result. There are alternative treatments for the upper part behind the parcel shelf. Either put felt on this panel on the engine side, or if the car is dismantled anyway, the felt can be put on the passenger compartment side where it is hidden by fascia and parcel shelf. These are the most important places. Further smaller reductions can be achieved by putting felt on the front wheel arches where they are visible within the car, and by putting felt on the underside of the parcel shelf, which helps to reduce reflection of the remaining noise which enters the car. To reduce the penetration of gearbox noise the front part of the tunnel where the gearbox is can be lined with felt on the underside. This needs the gearbox out. Use a waterproof glue for this situation. Alternatively, felt the top of the tunnel, but this may be less aethetic as it makes the carpet bulky over the tunnel. Wind noise can be reduced by renewal of the seals on the doors and windows, and by making sure that the doors and windows all fit properly - this also reduces rattling. Little can be done about preventing road noise entering the car but I have never found it a great problem, and absorption within the passenger compartment is the best solution.

Absorption of sound already in the passenger compartment. Use thick felt under the carpeted areas, and choose a carpet which has a soft surface. Once the noise is inside the car, the main task is to absorb the noise, and soft surface materials are best for this. There is only a limited extent to which this can be done in an A30/35 without customising it, because the original surfaces were mostly hard, either exposed steel or rexine. Modern cars have a very high proportion of textile surfaces. When replacing the headlining, ensure that the felt is attached to the roof, because this provides a major amount of absorption against drumming. If a non-standard headlining is acceptable, the headlining can be replaced by glueing foam to the roof and then gluing material directly on top of it, producing a soft sound absorbant surface. Further absorption can be obtained by felting under the rear seat squab, though the effect on rear axle whine penetration is minimal. Naturally, using soft padded material for the door panel trim and covering the interior metalwork with sound absorbant material would make the car quieter would make a substantial further reduction in noise levels. There does not seem to be any benefit from felting the boot area.

Vans are inherently much noiser because of the large nearly flat panels, but padding the carrying area with felt should reduce drumming substantially.

In conclusion, there is a limit to what can be achieved. Unfortunately the saloons (I have no direct experience of vans) have a whole body resonance which is brought in by an engine speed of about 4500 rpm, and I have found no way of eliminating this. If it occurs at an inconvenient speed, the solution is a change of rear axle ratio, but this affects the vehicle's performance.

Whilst great care is taken to ensure that the technical information and advice offered is of the highest standard, neither the author, nor The Austin A30/A35 Owners Club, or the Officers of the Austin A30/A35 Club accept any liability at law for any death, injury or loss whatsoever arising from the use of advice contained in this article.