Tinker Talk – September 2019: Gimme a brake

By Justin James

The moment a soccer mom all jacked up on wine and prescription meds whips into your lane is not the best time to test your brakes. A soft or spongy feel at the lever is a clear indication that your brakes will not react or grab at full power in a moment of need. Depending on the type of brake fluid your bike utilizes, over time it will either break down or absorb moisture, leading to a poor feel and loss of performance. Luckily, this can often be remedied by simply bleeding the brakes as follows.

• Obtain a suitable brake fluid for your application. Never mix DOT 5 (silicone) with DOT 3, 4 or 5.1 (glycol). DOT 3, 4 and 5.1 can be

interchanged in a pinch but this will alter the boil point as well as the feel. Refer to the brake fluid chart.

• Remove the rubber cap on the caliper bleed fitting. In some cases, there will be more than one (Photo 1).

• Remove the cap from the fluid reservoir. Sometimes it is helpful to unsecure the reservoir and move it to a more accessible location (Photo 2).

• Affix a clear line to the bleed fitting(s). I like to use a 1-way check valve to speed up the process, but the brakes can be bled just fine without one. Route the hose into a container to catch the fluid (Photo 3A).

• Adjust the fluid level so that it is between the low and high marks on the reservoir. Try to maintain this fluid level throughout the entire process. If you allow the fluid level to drop too far you may introduce more air (which is what you are trying to expel) into the system (Photo 3B).

• Pump the brakes a few times, then give them a good squeeze and hold the lever. While holding the lever, use

a small wrench to open the bleed fitting. If there are no obstructions in the brake system you should see a combination of fluid and air bubbles coming through the line (Photo 3C). Release the lever and close the bleed fitting. You will need to repeat this process until the lever pressure increases and there are no air bubbles visible in the clear line. (Photo 3D).



• Verify that the final fluid level is between the high and low marks on the reservoir and reinstall the reservoir cap.

In a healthy braking system, fluid should shoot out of the bleed fitting under pressure and lever resistance should increase as the air purges. If this ends up not being the case after a proper bleed, you may need to advance to flushing the system or overhauling the caliper(s) and/or master cylinder. Examine your brakes regularly!!!

Tinker, Shred, Destroy, Repeat

-Justin James (follow more of my Tinker shenanigans on Instagram @justinjamesmoto)

*You can now purchase my products to aid in your Tinkerings from www.usapartsco.com