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How moisture is a hazard to your brake fluid
By Jack Biddle • 21/03/2015
REGULAR SERVICING IS IMPORTANT, WRITES JACK BIDDLE
Vehicles used to give some sort of feedback or warning signals to the driver when it was time for a tune up or general service.
Engines started to run rough, a rattle from the exhaust meant a bracket or mount had broken while the brake pedal often needed a couple of good extra pumps to regain a firm feel beneath the driver's right foot.
The big positive from the repairer's perspective then, was that when owners drove away, there was an instant and noticeable difference.
With the new motor vehicle that's no longer the case. Modern technology means brakes self-adjust, electronic ignition has replaced distributor points while fuel injection has removed the need to clean and retune the carburettor.
Yes, you are still expected to take the car in for a service but it's getting a lot harder for workshops these days, particularly for those owners who have that "if it ain't broke, then why fix it" mentality.
One of those must-do jobs recommended by mechanics is usually replacing the brake fluid.
Why bother? The brake pedal probably feels fine. The pedal is firm, the vehicle stops perfectly well on request, plus there have been no braking issues in the past when it came to Warrant of Fitness time.
Hydraulic brakes work on the theory that you can't compress a liquid, so a specific type of brake fluid is used which has a high boiling point to withstand the temperatures that can at times build up in the brake system.
For example, heavy and repeated braking when descending for long periods can raise the brake fluid temperatures significantly.
The danger of not changing the fluid regularly is its boiling is lowered because brake fluid is hydroscopic and therefore can, and will over time, absorb moisture. The main source of the moisture absorption is through the flexible rubber hoses.
So when the brakes get a hard workout and the fluid temperatures rise, water within the system can reach its boiling point and vaporise.
And while you can't compress a liquid you can compress a vapour - the end result is a spongy brake and a drop in braking performance.
Have you ever noticed the brake smell from some vehicles when standing at the bottom of a long and steep hill? The smell is an indication of just how hard those brakes have been working which translates into a rise in brake fluid temperature.
Reputable garages can test the brake fluid and check the moisture content, while others will stick to the manufacturer's recommendations.
While brake fluid has corrosion inhibitors added, over time they will become less effective which leaves the internals of a brake system vulnerable to corrosion because of the introduction of the moisture.
So once the brake fluid has been changed are you going to notice any immediate difference? The answer is highly unlikely, but if changed for the right reasons it will make the vehicle a lot safer and reduce the risk of brake-related problems caused by corrosion further down the track.
Note: Changing brake fluid is not a recommended DIY job on the modern motor vehicle.