Stop It! Brake Fluid 101

I was working on a forklift this morning, and when I checked the brake fluid, I grimaced involuntarily. While the level was fine, it had the appearance of a strong cup of black coffee. I enjoy my java strong and black, but brake fluid should never have that appearance.

black brake fluid

Anyway, it got me thinking about brake fluid and maintenance. So, here’s an overview of the 4 types of fluids used in material handling equipment. Plus I have a link where you can find brake fluid here.

DOT 3: This is the most common brake fluid in forklifts. It is also what is normally used in cars. Dot3 fluid is very hygroscopic, which means it absorbs moisture from the air. This absorbed water will build up in the system and  cause rust and drastically reduce the boiling point of the fluid. This can cause spongy or failed brakes if the fluid is heated during hard braking. Systems designed for DOT3 are NOT compatible with oil or silicone based types of brake fluids. Any oil in the system will cause seals to swell and fail. Usually the first sign is a master cylinder that will not replenish. If oil gets in the system, it must be flushed out and all rubber components replaced.


DOT 4: This is compatible with DOT3. They are both polyglycol base, but DOT4 has some extra additives to raise the boiling point. This also raise the viscosity somewhat. The extra temperature tolerance is usually an unnecessary factor for material handling equipment. Originally designed for high performance  cars, it is common now in many passenger vehicles.

DOT 5: This is the oddball of the group. DOT5 is chemically different from DOT3&4. While the other two are polyglycol based. this one is silicone based. DOT5 is rarely used in cars, as it compresses slightly, giving a spongy pedal feel, but is common in electric forklifts. It is not hygroscopic, meaning it does not absorb water. Seals in a DOT5 system are not compatible with other fluids.

Mineral Oil:  This is most commonly used in rough-terrain lifts, but is also used in internal disc systems. Again, beware of contamination with glycol-based fluids. I once installed a master cylinder on a LiftKing, only to have it fail within a very short timeframe. Upon “autopsy”, I found that the part manufacturer had mistakenly used glycol-resistant seals. They had promptly swollen, started breaking down, and blocked off the replenishing port in the master cylinder. After installing a new master cylinder( with the proper seals), I had no more issues.


All types of brake fluids are subject to contamination and breakdown, and should be flushed at regular intervals. DOT3&4 should be checked often with a moisture meter or test strips to detect unseen water contamination.

If you need brake fluid here is a link to a great source page:

Brake Fluid

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What have you seen with improper fluids or contamination issues? Let us know, leave a comment below!

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6 thoughts on “Stop It! Brake Fluid 101

  1. Great article. Brake Fluid is often overlooked, which is sad considering it transfers the force we need to be able to stop our car. And just as important, brake fluid protects our brake system from corrosion. High levels of copper corrosion inside brake fluid will tell you when to change it.

    Liked by 1 person

  2. +1 on Jeremiah’s comment.
    In fact, be cautious in the retail world urging customers to change brake fluid based on moisture content . . . To mt knowledge, no vehicle manufacturer provides a guideline on this.
    There are however test strips that test the copper content of the fluid. The copper leaches out of the steel brake lines.
    To quote: The Automotive Maintenance and Repair Association (AMRA) recommends to its members that (1) auto Brake fluid be tested for contamination at OEM recommended brake system inspection intervals, and (2) that a Brake fluid replacement service be performed, for most vehicles, when testing shows copper content exceeds 200 ppm. The AMRA Technical Committee reached these conclusions after extensive study of industry data, including a review of SAE Papers, US Government reports (NHTSA and NIST) and independent laboratory studies, among other resources. The data showed that this increased presence of copper contamination predetermines the rapid growth of iron contamination and corrosion which has shown to impede future brake system performance. ”
    Bob Miller
    Train Them Now, LLC

    Liked by 1 person

    1. Great observations. In fact, I am going to contact Pheonix Brake Systems (the strip manufacturers) and ask them to provide 10 samples that I can give to my subscribers (chosen randomly) to help them see the value of this important test. Stay posted!


  3. Update: Pheonix Systems has kindly offered 10 free kits for my subscribers! Subscribe today for a chance to get YOURS!
    Much thanks to Pheonix Systems…I was impressed by the generous attitude and great customer service.


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