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Fast lap times and horsepower are pointless if you can’t stop your motorcycle. And you can’t do that if your brakes aren’t working.
(And no, “laying her down” isn’t an option.)
But how do your motorcycle brakes actually work? What is it that actually makes your bike stop?
In this blog post, you’re going to learn:
- How your motorcycle brakes work
- Components of Disc and drum brakes
- The differences between DOT 3, 4, 5, and 5.1 brake fluid
- About something deadly that might be in your drum brakes.
How do motorcycle brakes work?
Most motorcycles use a hydraulic brake system. What this means is that you squeeze the front brake or step on the rear brake pedal, the following happens:
- A pushrod is pushed into the master brake cylinder
- The piston’s movement generates hydraulic pressure, transmitting it through the brake lines to each wheel’s brake assembly
- Once the pressure reaches the brake assembly of each wheel, the brake’s caliper pushes the pistons towards the rotor (or disc)
- The pistons in the brake caliper press the brake pads against the rotor, bringing the motorcycle to a halt.
Disc brakes components (and what they do)
In 1969, Honda released the CB750 – the first mass-produced motorcycle equipped with a disc brake as standard.
Since then, most modern motorcycle brakes have used disc brakes.
Compared to drum brakes, disc brakes are much more effective at dealing with heat and require less maintenance.
A disc brake consists of a:
- Brake caliper
- Brake pad
The brake caliper
The brake caliper houses the brake pistons and brake pads into position.
There are two types of brake calipers: floating and fixed opposite-piston:
- Floating caliper: has one or more pistons inside on side that moves in a linear pattern as the brake pressure increases
- Fixed opposite-piston caliper: has a piston mounted on one side
The rotor (or just “disc”)
The rotor connects to the wheel hub. When the brakes are applied, the brake pads press against the rotor rather than directly against the wheel.
This friction between the pads and the rotor is what makes the bike stop.
The brake pads
This is the part of the disc brake that does the most grinding work. When the brake pad presses against the wheel to stop the motorcycle, it “grinds“ against the rotor, bringing it to a stop.
Because of this, brake pads thin over time. As a general rule of thumb, it’s a good idea to replace brake pads when their thickness is below 3 mm.
Drum brake components (and how they work)
Drum brakes were common on older motorcycles. Some modern ones are still fitted with this type of brakes, although usually only at the rear wheel.
Given how powerful disc brakes are, if you have a rear disc brake and you apply the rear brake too hard, you could lock up the wheel.
If this happens, it could throw you over the bike in what’s often called a “high-side.”
A drum brake consists of:
- A pair of brake shoes
- A wheel cylinder
When you apply the brakes, the brake shoes expand, which brings the bike to a stop.
After you release the brake, the return spring releases the brake shoes.
As simple as the mechanism is, drum brakes are more prone to overheat than disc brakes.
And now for the big question:
What could be in your drum brakes that could kill you?
Do you have an older motorcycle? Like, say, one that was made before 1970?
In that case, pay close attention – you’ll thank me.
Older motorcycle brake shoes sometimes contain a little extra ingredient called “asbestos.”
Yes, you read that right – asbestos – as in that thing that:
- Destroys your lungs over time
- Causes suffocation
- The song “Blue Sky Mine” by Midnight Oil is all about
It’s not a guarantee that your drum brake contains asbestos, but given how even a small dose can be hazardous to your health – be extremely careful when you’re dealing with drum brake shoes.
If you disassemble your drum brakes, make sure you wear gloves and either a face mask or some kind of anti-asphyxiation mask.
What Brake Fluid Do I Need?
Regardless of whether your motorcycle has disc or drum brakes, you need a certain fluid that runs through the hoses and pipes in your braking system.
That certain fluid is brake fluid.
Since brake fluid has an important task, it must among other things have:
- A high boiling point (above 230 C or 446 F)
- A low viscosity level (especially if your bike has ABS)
- The ability to not damage any parts in the braking system (e.g. rubber gaskets)
Brake fluid is divided into four categories:
- DOT 3
- DOT 4
- DOT 5
- DOT 5.1
Generally speaking, the higher the DOT number, the higher the boiling point will be.
DOT is glycol-based, but since it has a low boiling point (around 205 C or 401 F), this brake fluid is largely outdated.
Just like DOT 3, DOT brake fluid is glycol-based. However, unlike DOT 3, DOT 4 brake fluid has a higher boiling point (270 C or 518 F), and is, therefore, the most commonly used type of brake fluid.
Most modern motorcycles are built to run on DOT 4 brake fluid.
DOT 5 is different from all the other brake fluids in the sense that it’s silicone-based. Because of this, DOT 5 brake fluid doesn’t offer much protection against corrosion.
It also has a high viscosity, meaning that it’s not appropriate for modern motorcycles with ABS.
Here’s where things get complicated. DOT 5.1 is often confused with DOT 5 – but they’re not the same.
First of all, just like DOT 3 and DOT 4 brake fluid, DOT 5.1 is glycol-based.
It also has a high boiling point (about 270 C or 518 F), but absorbs water more easily, and must be replaced more often.
Glycol vs. silicone-based brake fluid
As I just mentioned, most of the brake fluids listed above are glycol-based. But what does this mean?
It means that they:
- Absorb water over time, which negatively affects the braking system.
- Are corrosive and damaging to paint
- Can be mixed with other glycol-based fluids (although this is not recommended)
DOT 5 on the other hand is silicone-based, meaning that:
- It’s not corrosive to paint
- It doesn’t absorb water as glycol-based fluids do
- Requires more maintenance than glycol-based brake fluid
IMPORTANT: Never mix glycol and silicon-based brake fluids. If you do this, your brakes will be very unstable.