Brake Fluids

Every driver knows that automotive fluids need to be regularly flushed and changed. Motor oils and coolants should be changed following the recommended maintenance schedule outlined in the owner’s manual, and such things as transmission fluids need to be inspected and changed regularly as well.
What about brake fluid?
If you ask a driver, they will likely look at you quizzically: Brake fluid? That has to be changed? Don’t you do that only when you get new brakes?
The reality is brake fluid needs to be changed regularly, just as motor oils, transmission and coolants need to be changed. The challenge for independents is educating drivers on making brake fluid  changes a part of a regular maintenance schedule.

Educating the Customer

The biggest hurdle a service writer will face is first explaining to a driver why changing brake fluid regularly is something that has to be done regularly. Most drivers know that not changing your motor oil or coolant regularly won’t kill you; it will just hit your pocket book very hard as contaminates build up and damage critical systems in an engine. The problem is that not changing brake fluid regularly will not only be costly it could very well cause the diver to have an accident.
So the first thing that has to be done is make sure the vehicle owner understands that changing brake fluid regularly is not just a maintenance issue, but a safety one as well. It will be productive to first give a quick explanation to the vehicle owner of what brake fluid is as most have no idea that there exist different kinds of fluids and what brake fluid does or how it behaves over time.
The thing to first remind a vehicle owner is brake fluid acts as corrosion protection and lubricates the brake system components. A regular change of the fluid also helps the fluid better withstand the heat produced during braking. Old brake fluid will be less able to do so.
There are two common kinds of brake fluids used in today’s automobiles, those based upon Polyalkylene Glycol Ether and those containing Silicone or Silicium-based Polymer. Polyglycol Ether-based fluids are the most common brake fluids out there and come in a variety of designations, DOT 3, DOT 4 and DOT 5.1.
What is unique about these fluids is that they are hydroscopic. This means that they can mix with water and still perform their function in the brake system. Silicone-based fluids, referred to as DOT 5, are non-hydroscopic, so they will not absorb or mix with water.
Water is the enemy
So what does all of this mean to the driver of the vehicle?
Wally Marciniak, director of technical service with Affinia Under Vehicle Group provided a useful overview to SSGM Magazine of the safety issues surrounding brake fluids that will help a service writer answer this for a vehicle owner.
Take the issue of moisture. You can’t avoid it. It is all around us, from rain to the moisture that is in the air. Ethylene Glycol-based brake fluids will over time absorb moisture from the surrounding air. That does not sound like much of an issue, but in reality it is. Brake fluid is made to have a high boiling point to withstand the high heat produced when  the vehicle brakes. When new and without any water in the mix, brake fluid will boil at about 260°C. When moisture gets into the system that boiling point drops and can drop to the level close to that of ordinary water.
When this happens, the brake system is compromised.
Now, it has to be admitted that old brake fluid will work well for most normal driving conditions. When applying the brakes, the brake fluid will get warm, but it will likely never get to its boiling point which has been reduced by the accumulated moisture. The problems happen when the brakes have to work much harder than normal, say in a sudden brake stop from a high speed on the highway, for example; or when pulling heavy loads and the brakes have to work much harder and longer in order to stop the vehicle and the load it is pulling. Or when the car has to operate in very hot weather and there is a lot of stop-and-go traffic.
In badly deteriorated brake fluid the driver may discover that when applying the brakes the car simply does not stop.

Is there a safe amount of water?
Because moisture is the enemy, it is recommended that service shops regularly check and change break fluids every year or two years. A good ‘rule of thumb’ to follow is that if the fluid tests has two per cent moisture, it is recommended to change the fluid; if it gets to three percent, the brake system must be changed. According to the Car Care Council, two years or every 24,000 miles is the recommended change interval, and brake fluid should be changed every time new brake pads and shoes are installed on a vehicle.
To break it down for the vehicle owner, remind them brake fluid will absorb about one per cent of moisture per year, so by the time a vehicle reaches two years, the brake fluid could have a moisture level of two or three per cent. A two per cent level of moisture in the brake fluid will reduce the boiling point of Polyalkylene Glycol Ether DOT 3 brake fluid to some 75°C and DOT 4-rated fluid to 45°C.
In any case, when it comes time to change the brake fluid, the whole system must be flushed. Drivers will sometimes confuse brake bleeding with flushing. There is a difference, and not just in terms of cost. A brake bleed normally involves a bleeding the air out of the system. Flushing is different as it is removing the old brake fluid and replacing it with new brake fluid. It is a more time consuming process and more expensive, but it has the important advantage of make sure contaminates are flushed out of the brake system and new fluid is now operating those systems for improved braking performance.