Importance of Breathers in Gearbox and Other Car Components

The design of modern cars includes a large number of components and assemblies, which are filled with technical fluids and lubricants. During operation, these fluids heat up, in other words they increase in volume, thereby increasing the pressure inside the car components and internals. Such car components as engine, gearbox, and axles are sealed (there is no venting to the atmosphere), thus there are pressure differences between the pressure rates inside car units and the air pressure. This pressure difference must be leveled out to prevent depressurization, fluid leaks, and damages of car elements. For this purpose, some car components are equipped with a special valve, known as the breather.

Breathers are installed on the following components:

• Gearbox
• Engine
• Front and rear axles
• Transfer Case

Cross section of the original breather valve

It is worth noting that breathers perform almost the same functions regardless of their installation place. In this article, we will consider the gearbox breather, its purpose, design, and principle of operation.

Breather: principle of operation and its peculiarities

A breather (or breather valve) is a special accessory which helps sealed car components (gearbox, engine, axles) to be vented to the atmosphere and maintain pressure balance.

On the one hand, breathers allow to relieve excess pressure (level the pressure during heating or cooling), and on the other hand, they prevent fluid leakages. When the gearbox (or engine) cools down, breathers prevent dirt, moisture, and dust from getting inside the gearbox. Thus, this small element became an indispensable part in design of modern gearboxes. The gearbox breather is mounted on the gearbox housing.

DPO/AL4 Breather for Peugeot Citroen Renault OEM

The car gearbox is responsible for torque conversion from the engine and its further transmission to the driving wheels. Gearboxes are filled with fluid, which expands its volume in the course of the gearbox operation. As a result, the pressure inside the transmission increases, and it must be released. If the pressure is not released, it will lead to the fluid leakages via gaskets and seals.

Breather located on the Allison transmission case

Fluid leaks inevitably lead to reduced lubrication of transmission elements, resulting in their premature wear. Initially, the process of gear shifting becomes more difficult, after that drivers may hear abnormal noises (roaring, vibrations). If car owners disregard these symptoms, then they will have to deal with failures of synchronizers, bearings, gears and other transmission elements.

Learn more about crankcase breathers

As for an internal combustion engine, the pressure in this component grows quite rapidly, due to high temperatures, and a part of end gases inevitably penetrate into the engine housing. To prevent engine oil leaks caused by increased pressure, this pressure is released through the breather. When the engine stops operating, the pressure inside the engine crankcase and in the atmosphere levels out by the airflow from the atmosphere through the breather. The engine breather prevents dirt and moisture from getting inside the engine case. Thanks to this quality, breathers became indispensable for off-road vehicles.

Transfer case breather

Front and rear axles also operate with the help of oil, and their internal space must be open to the atmosphere in order to avoid pressure increase inside the unit. For this purpose, the design of front and rear axles includes axle breathers.

Rear axle breather

Another important feature of the breather (on transmission, engine, or axles) is protection from dust, dirt, water, etc. It is especially important for the car axle, because it is an exposed element (for example in SUVs) and can be dipped in water or dirt during off-road driving.

Useful Tips

As a rule, it is necessary to regularly check the condition of all breathers installed on your car (engine breather, gearbox breather, axle breather). The thing is that oil particles can be squeezed out through breathers, and it may lead to severe contamination. In practice, breathers must be timely dismantled and cleaned of dirt and remaining oil.

The process of cleaning includes the following:

The breather is mounted on the gearbox housing

You will need a wrench to remove the gearbox breather

Then you have to remove the breather and O-ring

Wash out the breather ( you can use gasoline for this purpose) and reinstall it

If we talk about the gearbox breather, it is also necessary to know how to remove the breather accurately. On some cars, it is enough to remove the rubber cap and clean the valve. On other models, the breather (without a rubber cap) is located on the 5-th gear cover. It is also necessary to carefully clean the installation seat of the breather from dirt (so the new breather won’t fail prematurely). It is necessary to ensure that the breather cap can move freely in all directions.

Transmission fluid leak through the breather cap on the DSG7 transmission

In case if the cleaning procedure does not bring positive results (oil still leaks) then it is likely that the breather is damaged and it must be replaced. Drivers should pay particular attention to the rear axle breather. This breather is usually subjected to severe contamination. If the breather becomes contaminated or stops operating properly, it will lead to increased pressure and as a result, oil leakages. In this case, you should start with cleaning. After that, it is recommended to drive 20-30 kilometers. If it doesn’t help, then you have to replace the axle breather. If this measure also does not solve the problem, then the issue is not related to the breather.

Summary

In the light of the information provided above, it may be asserted that the gearbox breather, in spite of its apparent simplicity, plays an important role in operation of the whole unit. Thus, it is necessary to check regularly the condition of this element. It is especially important for SUVs, trucks, and special vehicles, which have breathers mounted on gearboxes and engines, and also on axles. Such vehicles often operate under harsh conditions, and as a result, the gearbox breather or axle breather can be contaminated or fail much faster (especially axle breathers) than in passenger cars.

If the gearbox breather gets out of order, it may lead to serious failures of the whole gearbox unit. Therefore, each visit to the repair shop for a regular check-up and maintenance services must include checking and cleaning of all breathers mounted on different car components. Finally, it is worth noting that regular monitoring of the breathers state makes it possible to prolong the service life of the gearbox (engine, or axles). If breathers are heavily contaminated, then it’s better to replace them instantly, since breathers have affordable prices.