A brake fluid flush is one of the most frequently forgotten car service items. Many motorists don’t even realize that a brake fluid flush is a vital item that is on their service schedule and others feel as though their mechanic is trying to take advantage of them or sell them a costly service item that they do not need. Let us assure you that on the good advice of Ate, the inventor of the hydraulic disk brake system, nobody here is trying to take advantage of you; a vehicle’s brake fluid does need to be flushed periodically and without doubt will help prevent costly brake system repairs.

The primary reason brake fluid should be periodically flushed is because it is hygroscopic, meaning that it readily absorbs and retains moisture, actually within the chemistry of your brake fluid. This just happens like the carbon dioxide gas that dissolves into your cola or even beer.  It may vanish from sight but it is no different to the water hiding between the grains of sand in a bucket of wet sand. This might seem a bit odd as a goal but, that is exactly what we want the brake fluid to do. Understanding that many of the brake system components are made from metal, we can quickly see that moisture is the enemy that can and does cause corrosion. Brake fluid, by absorbing any moisture that gets into the system and retaining it, helps to prevent this moisture related corrosion and failure of internal brake system components. Chemistry being an exact science, even the highest quality brake fluid can only retain so much moisture, so it must be periodically purged from the system and replaced with new fluid. The difference between new and contaminated fluid does become obvious after a while, just look at the image below!

There is specialist test equipment available to help determine when the fluid needs to be changed but this sort of testing is somewhat of an overkill. The hygroscopic nature of brake fluid means that it deteriorates over time, it always happens, it happens to every make and model of car and there is nothing we can do about it. Remember that the moisture that is absorbed into your brake fluid is moisture which is no longer corroding your brake system. Failing to flush away the contaminated fluid is just removing this important safeguard.  Left in contact with the internal metal components of your brakes this moisture makes an ugly mess!

As a good general rule of thumb the service interval for your modern vehicle’s brake fluid flush is every two years, especially as all of our vehicles are now equipped with ABS braking systems and brake based vehicle stability controls. Years ago, prior to the advent of antilock brakes, flushing the brake fluid was not as much of a concern. The more intricate fluid circuitry of the hydraulic control units on today’s antilock brake and traction/stability control equipped vehicles are is more sensitive to moisture and small particulate debris. Your badly contaminated fluid can be heavy, thick or even waxy in texture, especially where it is hidden away in your brake calipers. This will ultimately cause seized brake parts or even complete failure of the ABS function on your car which is an instant NCT fail. Few motorists are remotely aware of the temperatures that braking generates either, temperatures that simply accelerate the breakdown of your brake fluid. 

“What does all of this mean?” you ask. Well simply put, your brake system efficiency will deteriorate, something that the NCT test will hopefully detect for you as the other likelihood is a failed component such as a caliper, ABS system or brake proportioning valve. Completely aside from the obvious risk to yourself and others while your brakes are defective, repairs to any of these brake system components could cost hundreds of Euro so the small amount of money spent on a brake fluid flush every two years is well worth the price and of course, that peace of mind.