Brake Fluid Flush

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Reader Question

I brought my 2000 Chevy S10 for a routine oil change. I got talked into
having my brake fluid flushed at a cost of $89.00. The mechanic said it
was dirty and needed flushing because of the ABS anti-locking brakes. I
told him I never heard of that before. My truck only has 23k miles on
it. Was I ripped off?

Thank you,

Joseph

Hi there Joseph,

I know you must have been a little surprised to hear your truck needed to have the brake fluid replaced. But actually, this mechanic was probably doing you a good deed.

Brake fluid attracts moisture, and this moisture can rust the insides of the brake system. This moisture was not that big of deal 10 years ago, but on ABS brake systems of today, the rust and other debris that accumulates in the fluid can do lots of internal damage and can be very costly.

Brake fluid can also break down over time from excess heat that is created from within the brake system.

At my shop we recommend flushing the brake fluid system about every 30,000 miles, or whenever we are performing a brake job. To do this flush, we open the brake lines located at each wheel and allow the brake fluid from the brake master cylinder to “gravity bleed” as we continue to feed new fluid to the master cylinder until the fluid runs clear at all wheels.

By gravity bleed I mean without the assistance of anything other than
allowing the fluid to slowly drip from the lines by the natural force of
gravity.

You are probably familiar with the term “bleeding the brakes” when talking about a brake job. When the brake lines are opened or any work is performed to the brake system that can allow air to get trapped within the lines, the brakes must be bled of air.

In the earlier days, the mechanic would bleed the brakes by having someone pump and hold pressure on the brake pedal as he opened the brake lines located at each wheel. This method of bleeding the brakes is not a recommended procedure for newer brake systems (discussed later).

What is the difference between flushing and bleeding?

Flushing is just that, flushing the old dirty fluid out of the system and replacing it with new clean fluid. Bleeding usually consists of removing just enough brake fluid to get out the air pockets that have become trapped in the system, and usually does not focus on the time consuming process of removing the dirt and old fluid from the system.

One side note learned by experience. If you are interested in doing a brake fluid flush on your own vehicle, be warned of the potential dangers. Foremost, follow the brake bleeding procedures outlined in the repair manual you should be using.

Stepping on the brake pedal with the brake lines cracked open can cause the dirt and debris to be pushed into the body of the master cylinder, thus causing damage to internal parts and seals of the master cylinder and the anti-lock brake components.

Stepping on the brake pedal as someone under the vehicle opens each brake line at the wheel used to be the way you bled brakes, but not anymore.

Gravity bleeding does take a little longer to perform and can require a lot of new brake fluid to push out the old dirty fluid, but the risk of doing internal damage to the anti-lock system is greatly reduced. They also make vacuum assisted brake bleeding and flushing equipment to help speed up the process.

How can you tell if your vehicle is due for a brake fluid flush?

They make special test strips which can detect high levels of moisture present in the brake fluid, but I prefer the old fashioned eye ball method personally. Remove the brake master cylinder cap and visually inspect the condition of the fluid.

Brake fluid (picture) should be clear or a slight yellowish tent, so black or dark
colored dirty fluid should be quite obvious even to the untrained eye.

You can get excellent tips like this and advice on how to not get ripped off by your mechanic from my ebook “What Your Mechanic Doesn’t Want You to Know”

Click Here to learn more.

Blessings,
Austin Davis

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Posted in: Brakes

About the Author:

Austin Davis, consumer car repair advocate. "Hi there! I love to help people solve their car repair problems and I hope my site was helpful to you today. Thank you for stopping by."

6 Comments on "Brake Fluid Flush"

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  1. Yes some moisture and debris can get inside the lines. Gravity bleeding each wheel for about 2-3 minutes should be enough if you have a constant drip of flui (dont let the reservoir go empty). Can be hard to tell when new fluid has been reached, a styrofoam coffee cup sample works well but each vehicle is a little different due to its past maintenance intervals and wear and tear. Removing moisture is the main focus

  2. james weigand says:

    this is one of the first suggestions that makes sense. I change the fluid in the reservoir whenever it gets dark[and wipe the rubber "gasket/hat" to remove condensation.] does the fluid in the lines really get exposed to moisture? Will gravity bleeding clear all those ABS “loops” what is best way to know when fresh fluid reaches wheel cylinder if not real dirty ? [dealer mech let on they only change fluid in reservoir-helps prevent creating new problems]but this sounds like the way to go !

  3. Austin Davis says:

    Start with removing all 4 wheels and check wheel cylinders, brake hoses and metal brake line fittings and brake calipers for leaks. Then make your way to the brake master cylinder on the drivers side firewall under the hood and inspect for leaks there too. Sometimes a master cylinder can leak INTERNALLY and cause a spongy brake pedal and turn the red brake warning light on, although there are no external fluid leaks.

  4. josephine ertell says:

    not sure where break fluid is leakin from know the light is on

  5. Austin Davis says:

    You want to start with the farthest wheel away from the master cylinder, should be the right rear. Then the left rear then right front one at a time.

    It should be fine to bleed this system, just do not mash down on the brake pedal which pushes all the dirt and rust etc. into the master cylinder bore and can cause internal leaks.

    But honestly, unless you are doing brake pad replacement I don’t really see the need to do this at this point just for maintenance. I would wait until you do a brake job then do it.

  6. Nathan says:

    Hi Austin, I have a quick question regarding gravity bleeding the brake system. I understand the process where you just allow the fluid to run out from the valves until you begin to see clean fluid coming out.

    My questions are:

    1-can you gravity bleed all 4 valves at the same time or do you have to do 1 at a time?

    2-if you have to gravity bleed each valve one at a time, does it matter which order you go in or is there a specific order you follow?

    3-finally, I have an old 1994 Mitsubishi 3000GT (non-turbo) with about 103K miles on it and I honestly don’t know if the brake system has ever been flushed or not. Would it be a bad idea to flush the system at this point since new fluid can possibly cause cracks/leaks in the old brake lines?

    Please let me know your thoughts and the best approach to my situation.

    Thank you in advance for all your help.

    -Nathan

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