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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