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We usually remember to replace the brake pads, but the brake fluid is a bit less frequent, and practically no one remembers to replace the hoses... until the brakes unexpectedly fail or the diagnostician extends the technical inspection.
The condition of brake hoses should be checked by a diagnostician during a periodic technical inspection, as well as by a mechanic when carrying out ongoing repairs.
The average age of passenger cars on our roads is still over 14 years, so corrosion is a significant problem in some vehicles. There's no strict rule about how often hoses should be replaced. Their condition should simply be regularly checked. It's common for hoses to leak during the maximum braking performance test , which is mandatory during a periodic inspection by a diagnostician.
Inspecting the condition of hoses, both metal and flexible, should be performed much more frequently in off-road vehicles, as they are highly susceptible to damage. Damage to hoses can also occur in relatively new vehicles. This can be caused by improper or broken mounting, which can cause the hoses to rub against the wheel during cornering, quickly leading to abrasion and leaks. Increased attention is recommended, especially after installing higher-profile or significantly wider tires. Brake hoses operate in very harsh conditions, as they are located under the chassis, and in winter, the high salinity of the environment significantly accelerates corrosion and further prolongs the retention of moisture in the chassis.
Be careful with water!
Rubber hoses should be replaced if even the slightest cracks or abrasions appear, or as a preventive measure every 3-4 years.
In the case of metal pipes, when any mechanical damage or corrosion occurs - in practice this means a maximum period of 8-9 years.
Brake lines corrode not only externally but also internally. This phenomenon becomes more severe the less frequently the brake fluid is changed (the fluid is hygroscopic and tends to absorb water from the environment).
Water enters the braking system primarily through flexible brake hoses. This may be difficult to imagine, as these same hoses maintain a tight seal even at pressures exceeding 350 bar. The reason lies in the porous rubber material from which the hoses are made. The simplest way to explain it is as follows: brake fluid "absorbs" water from its immediate surroundings, i.e., the brake hose. To maintain its flexibility, the rubber brake hose seeks out lost water from its surroundings, i.e., the air.
And so the story repeats itself: the brake fluid absorbs water from the flexible hose again, and the hose replenishes the lost water from the air. The water absorption rate through the brake hose depends on the type of rubber material used and the hose length. In recent years, manufacturers have been systematically improving the composition of the mixture, gradually reducing this effect, thus extending the service life of the products.
The boiling point of brake fluid should be checked at every visit to the workshop. The permissible boiling point of brake fluid should not fall below 180°C (measured in the reservoir). Experience shows that the boiling point of the same fluid measured at the wheel can be approximately 30°C lower due to fluid waterlogging.
Wherein lies the hidden danger?
Glycol-based brake fluids are hygroscopic. This means they absorb water from the environment. Water entering the brake fluid lowers its boiling point. This can lead to the brake fluid boiling during frequent braking, leading to the formation of vapors in the braking system. Such air pockets in the braking system deform easily, preventing hydraulic pressure from being transferred. This results in significantly reduced braking efficiency – in critical situations, even down to zero.
Replacing hoses isn't difficult, provided you have good access. However, it's possible that the hoses are so corroded that attempting to unscrew the flexible hose will result in the metal being damaged. This should be taken into account when undertaking the repair, and you should be prepared for any additional costs.
sources
motofakty.pl
wikipedia.org