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Hydraulic Disc Brake Bleed Tips from Formula Brakes

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This is excerpted from the December email newsletter from Formula Brakes.  Check out their new 2010 brakes from Sea Otter and Interbike to see the latest stoppers.

Hydraulic Fluids 101. Part of your proper bike maintenance schedule should include having your brakes bled. This can be one of the most important things you can do to keep your brakes performing like new. We generally recommend having your brakes bled at least once a year, but if you are one of the lucky few who is riding more than 2-3 days a week, every 6 months is recommended. After you finish reading and decide your brakes need a good bleeding, check out our bleed instructions.

Why bleed? As your fluid ages, not only do the heat resisting properties of the fluid slowly diminish, decreasing the performance of your brakes, but debris accumulates in the fluid, causing accelerated seal wear. Because the performance degradation occurs gradually over a period of months, you often will not even notice it occurring. DOT fluid is hydrophilic, which means it absorbs water and moisture, even directly through rubber membranes such as seals and diaphragms. The more water and moisture your fluid absorbs, the worse the performance properties of the fluid get. Old fluid can cause lever pump up on descents, inconsistent lever contact points, and debris can hamper fluid transfer from between your reservoir and main chamber.

Fluid Choice: Your Formula brakes come stock with a high performance Shell DOT 4 fluid. It is also what we recommend to use during service bleeds. While we recommend name brand fluids from Shell or Castrol, in a pinch you can use any glycol based DOT fluid (such as DOT 3 or DOT 5.1). If you are faced with a myriad of choices, pick the DOT 4 fluid with the highest wet boiling point. Your local moto shop is a great place to look for the potent stuff. Remember to flush the old fluid out as completely as you can and be sure to use a fresh bottle as one that has been opened is already pulling in moisture. To recap:

  • Good: DOT 3
  • Better: DOT 5.1
  • Best: DOT 4

Warning!!: You should NEVER use silicone based DOT (such as DOT 5) or mineral oil (great natural laxative, but not so great for high performance disc brakes). Using mineral oil or silicone based DOT will RUIN every seal on your brakes – DO NOT USE IT! Trust us, rebuilding every seal is about as fun as pulling nose hairs.

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