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Technical focus: Motorcycle brake fluid


motorcycle brake fluid

It plays a major role in the braking quality of your motorcycle and yet it is often forgotten. Motorcycle brake fluid transmits the force you apply to the lever to the wheel. Do you know its specificities? Which fluid to choose for your motorcycle? When and how to replace it? We explain it all to you here!

What is the purpose of brake fluid?

Brake fluid is a hydraulic fluid used in motorcycle braking systems (and other vehicles for that matter) to transmit the force exerted from the brake control to the wheels. When the brake lever is squeezed, brake fluid is pushed by the master cylinder into the hydraulic circuit. It causes the movement of the pistons in the calipers which ultimately compress the brake pads against the disc(s) attached to the wheels. This instantaneous sequence causes the motorcycle to slow down and ultimately stop.

Hydraulic front brake of a motorcycle

Who says hydraulic braking says brake fluid – Photo Emmanual Thomas

We mainly require three qualities of a good brake fluid:

  1. Incompressibility, which allows the force exerted on the brake controls to be transmitted as efficiently as possible to the calipers.
  2. Good fluidity cold or hot, like engine oil. A liquid that becomes viscous would add dangerous resistance to pressure transmission.
  3. A high boiling point, so that it maintains its incompressibility properties under extreme temperature conditions. If the fluid boils, it loses this quality. This temperature can vary depending on the mixture used to make the brake fluid.

Brake fluid is hygroscopic, meaning it easily absorbs water from the air. It thus deteriorates little by little, irremediably. The presence of water lowers the boiling point and can also lead to the oxidation of certain components of the braking circuit. Reasons why this consumable must be replaced regularly with new product.

DOT, what does that mean for brake fluid?

All motorcycle brake systems (but this also applies to other types of vehicles, including airplanes) use DOT fluid. DOT is the acronym for “ Department of Transportation", the US Department of Transportation, which defines a performance standard for hydraulic braking fluids: performance of resistance to boiling, lubrication of moving parts, miscibility of liquids, compatibility with materials (metals, plastics and seals).

DOT liquids marketed in France must also meet ISO, AFNOR, SAE and FMVSS standards.

Different fluids and motorcycle parts to be replaced periodically

Brake fluid is one of the motorcycle consumables

The different types of brake fluid

DOT 3 liquid is a basic brake fluid, which appeared in the era of drum brakes.
Boiling point: approximately 205°C under good conditions

More advanced, dOT 4 liquid reacts better in the presence of water than DOT 3. It is the most common on our motorcycle brakes.
Boiling point: approximately 230°C under good conditions

DOT 5.1 liquid is a high performance product often used in competition motorcycles. It offers better performance in terms of temperature and lifespan.
Boiling point: approximately 250°C under good conditions

DOT 5 liquid paradoxically has nothing to do with DOT 5.1. Made from silicones, it is intended for certain types of specific braking systems, such as those of Harley-Davidson. Its purple color visually distinguishes it from the previous liquids.

Nissin brake fluid reservoir cover

The required DOT type is sometimes listed on the cover of the brake fluid reservoir

What type of fluid should I choose for my motorcycle?

Let's talk little, let's talk well: as with the rest of the parts related to braking, we often advise against choosing a "more efficient" fluid for " upgrade » your motorcycle as you would do with a suspension kit prepared to replace the original, for example.

To choose the correct DOT fluid, consult the user manual or maintenance manual for your motorcycle. Sometimes the information is directly on the lids of the brake fluid reservoirs.

The costs

Prices are between 20 and more €98.33 per liter depending on the quality of the products, knowing that DOT 3 motorcycle brake fluids are generally less expensive than DOT 4 and themselves than DOT 5.1.

Pay attention to the volume of the container: if the price of a container is much higher than its competitors, it may be due to a larger quantity of product!

Big brands : Motul, Castrol, Ipone, Motorex, putoline, Brembo , elf…

See our motorcycle brake fluid offer

replacing motorcycle brake fluid

Replacing motorcycle brake fluid is recommended at least every two years

When to replace your brake fluid?

The porosity of the joints ends up allowing humidity in the air to mix with the brake fluid, with the consequences mentioned above. We therefore advise you to replace the brake fluid on your motorcycle every two years at least, or even more often if you are a heavy rider.

When purchasing, choose small quantities of liquid. It is in fact not recommended to keep the liquid for a long time once the bottle has been opened, again because the liquid absorbs humidity.

Periodically, remember to check the level. As with the engine oil level, it is generally framed by “minimum” and “maximum” marks on the reservoir.

Be careful, this fluid can be aggressive with paints or varnishes. If spilled, wipe immediately with a cloth.

Motorcycle front brake with ABS

ABS systems can sometimes make bleeding difficult – Photo Hans Ripa

Bleed the brake fluid on your motorcycle

Bleeding used brake fluid and replacing it with new fluid are among these operations accessible to everyone with little tools. Be careful though if you have a front-rear coupled braking system (Dual CBS Honda type), which risks making bleeding more complex. Likewise, some motorcycles with ABS require more handling. If you have the slightest doubt, call a professional: you can't play with the reliability of your brakes!

If you get started, for less than €19.67, a brake fluid bleeder can make your life easier, but is not obligatory either. The bleeder is a valve that prevents the return of used liquid and air during the draining operation. It saves you time and new fluid.

How to purge? As is often the case in motorcycle mechanics, a good mechanical video tutorial is better than a long speech.

There you go, you know everything about brake fluid! Don't hesitate to ask your questions in the comments if you can't find the answer here.

Featured photo: ipone

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Loic

Editor and tester for Motoblouz , I am an unconditional fan of roads with bends. For me, the motorcycle is a means of escape as well as a means of transport.

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