How To Change your sled’s brake fluid, and why you should ... regularly

Materials – Just a few hand tools, a clear plastic hose, a clear container, and some new brake fluid is all you will need to do this necessary maintenance project.
There’s no question that your snowmobile’s braking system is important, but it’s often neglected. Here’s why it shouldn’t be, and how to keep it in top shape.

Brake fluid is an integral part of the system, yet many manufacturers don’t even offer any recommendations for changing it. They all say to inspect the braking system and check the fluid level and if it’s up, then all is OK. However, changing your brake fluid regularly can protect your system from expensive corrosion damage and ultimately extend your snowmobile’s life.

The right brake fluid
In the U.S., the Department of Transportation (DOT) regulates brake fluid specifications. DOT specifies all criteria and certain specifications that different fluids should meet, such as; the ability to flow in cold weather, the boiling point and compatibility with different types of materials within the brake system. DOT labels the fluids according to how they meet its different classifications, with DOT 3, DOT 4 etc. Today most snowmobile manufacturers use DOT 4 type brake fluid because it has a higher boiling point than other grades.

Brake fluid is glycol-based and hygroscopic, meaning it absorbs water. If you leave a container of it open, it will absorb water from the air. In the brake system, it will slowly (over years) absorb water through the rubber hoses and parts, which is not good as it changes the performance characteristics of your braking system.

When adding new brake fluid, be sure to check the owner’s manual or reservoir cover and make sure it’s the appropriate type for your vehicle. Don’t substitute DOT 3 for DOT 4 if your sled specifies DOT 4. However, if DOT 3 is recommended for your sled, you can use DOT 4 in it without problems.

Castrol also markets a brake fluid called LMA, for Low Moisture Absorption. This is formulated to last longer than conventional types because it takes longer to reach its saturation point, and also boasts a higher boiling point.

Finally, it’s important to note that DOT 5 brake fluid, which is silicon-based, is NOT compatible with conventional fluid and should NEVER be added to a system using DOT 3 or 4. DOT 5, which has a purple color, doesn’t absorb moisture, and has a higher boiling point.

Why change fluid?
Flushing your brake fluid is preventative maintenance because conventional glycol-based brake fluid absorbs water over time. Flushing keeps condensation from occurring in the brake system and causing corrosion.

Eventually, the brake fluid in your sled will absorb all the moisture it can hold, reaching its saturation point. Several things can happen then. Unabsorbed moisture can begin to collect in the system, causing corrosion in critical areas, water can cause seals to swell and deteriorate, further contaminating the fluid, and the fluid’s boiling point will drop beyond recommended levels. This means that under high-heat braking conditions, such as during hard braking or quickly repeated brake application, the fluid will boil sooner, which will reduce braking performance. The lever can begin to feel spongy, and as braking efficiency drops, basically it takes longer to stop your snowmobile.

How do you know when brake fluid should be flushed?
It’s recommend you change the fluid every two years, because of the climate and the constant changes in temperature in our sport. However, your eyes can tell you as well because fresh brake fluid is transparent and has a slight amber color. As the fluid absorbs moisture; it takes on a darker, cloudy appearance.

You also can verify that you need to change your fluid with a Brake Fluid Tester that can determine the boiling point of a fluid sample. Fresh brake fluid has a boiling point of about 400 F or higher. However, as it absorbs moisture the boiling point will gradually drop. It’s recommended you change the fluid if a tester shows a fluid’s boiling point below 330 F. These testers are expensive and not many shops have them, the cost of simply buying a bottle of brake fluid is much cheaper and more practical.

You often hear the phrase “steel-braided brake line” when people are talking about the specs of high-performance sleds. Steel-braided lines are superior to the braking feel of rubber hose brake lines. For example, if your friend has an X package MXZ, which has steel-braided lines, your standard MXZ (rubber lines) will never deliver as solid a feel in the lever as his X package.

The reason? The rubber hose expands under braking, while the steel-braided line remains solid.
How to change brake fluid
How to Change Brake Fluid

The Process - Find the master cylinder reservoir and notice the DOT 4 marked on its cover (1). Before cover removal, clean around the lid to prevent dirt from falling into the reservoir. Then taking the cover off (2) is easy. As you start the process, being able to see through the clear tubing and clear container (3) will be helpful. Make sure your fluid (4) is LMA (Low Moisture Absorption). It’s formulated to last longer than conventional brake fluids because it takes longer to reach its saturation point, and also boasts a higher boiling point. Try to keep the fluid level in the master cylinder above the minimum mark when flushing your brakes. As you flush you’ll notice air bubbles in the line (5), keep flushing the system until these bubbles are pushed into the container. You’ll discard the darker dirty brake fluid (6) and know you’re completely flushed when you see the clearer new fluid (7).
Brake flushing is much like bleeding air from the system. The most common method is the tried-and-true two-person procedure. It’s easier done than described and can be completed in 10-15 minutes.

STEP ONE: Remove the master cylinder’s lid from the left side of the handlebar (be sure to clean around the lid first, to prevent any dirt from falling into the system’s reservoir).
Step Two: Slip a piece of clear plastic hose over the bleeder valve on your brake caliper; it should fit snugly. Place the other end of the hose into a clear container, such as a glass jar or plastic milk
carton; submerged in brake fluid. (Being able to see through a clear container will be helpful.)
Step Three: Have the second person pump the brake lever a few times to build up pressure, then on an inward stroke, hold the lever in slightly.
Step Four: While your assistant is holding the lever in, use a wrench to open the bleeder valve just enough to let a surge of brake fluid escape into the hose and container.
Step Five: Your assistant should then slowly squeeze the lever and hold it there long enough for you to immediately close the bleeder valve again to prevent air from being drawn back into the lines. Repeat this procedure several times.
Step Six: The key is to keep the fluid level in the master cylinder above the minimum mark by repeatedly adding fresh fluid. Once you begin seeing fresh, clear fluid coming out of the clear tubing (with no air bubbles) that comes out of the bleeder valve (no longer old, dark fluid), you can tighten the valve. That’s it, you’re done.

Be careful not to spill any brake fluid, it can act as a paint remover so be sure to have a good clean up. Knowing that your brake system is in good working order will give you peace of mind and the ability to enjoy your ride.
Bob Island is a veteran snowmobiler and former Canadian snowmobile magazine editor who lives, and rides, in Ontario.
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