Brake Fluid Flush: Why Should You Care?

How brake fluid flush or replacement ends up in the mind of motorists is usually a mechanic recommends it. When the mechanic tells you that it is going to cost you $60 to $100, you think ”Hey, my car stops fine. Why should I care about that!?”

I could tell you that the National Traffic Safety and Highway Administration  (NTSHA) found that over 20% of  vehicles in a sampling had moisture content in their fluid that exceeded 5%. Or that in a Car Care Council survey found brake failure was on the minds of over half of the motorists they surveyed.

Unfortunately it is hard to understand something like brake fluid needing replaced when you can’t relate to it. Let’s try to understand some simple things to unravel it, shall we?

The brake fluid is the hydraulic fluid that is used to apply pressure via the calipers or wheel cylinders on the brake pads and or shoes to stop the car. That fluid does a great job, but looses it’s effectiveness as it absorbs moisture. The higher the moisture content, the lower the boiling point of the fluid and the more prone to brake fade your brakes are. Now you can understand that moisture (water) in the fluid lowers the boiling point possibly to a very dangerous level.

To further place things into a perspective that you can relate to, a normal stop from 60 mph generates enough heat to move a 1 cubic foot block of ice through the stages from ice to steam in under 5 seconds. That is a lot of heat! In a panic stop from that same speed the heat is even greater.

If we have old fluid in the system that has been heated and cooled many times during the normal operations of braking, that fluid becomes contaminated with moisture, dirt, rust and other things which attacks all the hydraulic components including master cylinder, ABS pump, calipers, wheel cylinders, lines, etc.

Most manufacturers have some suggested interval to perform a brake fluid flush. These intervals vary from 2 to 4 years and mileages from 24,000 to 60,000 miles. Experience has taught me this is too long between services.

Years ago when we performed brake services, it was a standard practice to “bleed” the brakes at each wheel when collapsing the caliper or cylinder to install new pads or shoes. Unfortunately two things have stopped this beneficial practice; the first is the manufacturers are no longer suggesting it be done; the second is as mechanics we have to work within the constraints of the shop owner and the customer. The shop owner wants it done faster and the customer doesn’t want to pay for it.

These items have significantly increased the cost of brake service because we now have more hydraulic parts being replaced and more brake discs (rotors) being replaced when the hydraulic component seizes and destroys them as a result of failing to perform a brake fluid flush.

If you want to have a safer car and one that is less costly to repair the brakes, then opt to have your brake fluid replaced about every two years or at least have the old fluid bled off at the wheels once a year.

There are lots of tools to check for moisture from strips to electronic testers like the Wagner Brake Fluid tester. Where the problem arises in using this equipment is that the mechanic must drain some fluid from one of the wheels (preferably a front) to test otherwise the readings are going to be false. They typically don’t want to do this as it takes their time and most car owners are under the false impression that “the mechanic is just trying to sell them something.” So if they do anything at all it is usually to test at the master cylinder. I have personally tested this at a wheel and the master cylinder and found a large discrepancy in the boiling points indicated. Want to guess which one had a lower boiling point?

Some would question why hasn't the car makers included a sensor that could be scanned using an OBD2 Scan Tool like the 2X80S in the brake fluid line to test brake fluid. But if they did that it would open up them to more law suits as the sensors fail from too much moisture attacking them, or from leaking which could reduce braking performance and or cause accidents. Some car makers have included a moisture sensor but it was placed into the fluid resovoir.

For The Professional:

Use whatever equipment you have in your shop and if you don’t have any then don’t be afraid to take this service on as you are doing your customer a very large service to increase or protect their car’s stopping power by performing this needed service. It does not require any of the sophisticated brake bleeding equipment to either bleed off some old fluid or a complete brake fluid flush. All that is required is a sufficient amount of fresh brake fluid and follow the manufacturers’ guidelines in bleeding the brakes manually.

Most times that procedure is to keep the master cylinder full with fresh fluid and start at the farthest wheel from the master cylinder. Allow the fluid to drain until it runs “clear”. Clear is defined as that golden look new fluid has. Close this wheel bleed screw off, go to the next closest, repeat the process. Continue the procedure until all wheels have been flushed.

I personally like turning a 12 ounce plastic bottle inverted into the master cylinder to supply the fluid until it gets exhausted, then switch to a new bottle. I have tested both procedures (equipment vs manual) for time needed to perform properly and both require almost the same time.