Tech FAQ: Park Tool Tech Tips
There were tech tips galore to be gleaned from the second annual series of hands-on mechanics’ seminars comprising the 2010 Park Tool Tech Summit. Here are some of them:
All hydraulic disc brakes:
Always clean around the outside of the piston (a Q-Tip with the brake fluid of that brake system on it works well) before replacing pads or before pushing pistons back in that have pushed out too far.
It goes without saying that you never put DOT (automotive) brake fluid in a brake designed for mineral oil, or vice versa, as the seals will be ruined.
DOT fluid absorbs water. Once you have opened a new container of DOT brake fluid (like for Hayes or Avid brakes), do not use it again once it sits more than a few weeks, even if the container is tightly closed. And if you leave the container open only for a few hours, that brake fluid is no longer usable. In a humid environment, you can leave a glass of DOT fluid on the counter for a day and it will overflow as it absorbs water.
Water in the DOT fluid will lower its boiling point substantially, causing it to boil at normal operating temperatures for the brakes. If the fluid ceases to be a fluid (because it is boiling), a hydraulic brake will no longer work. Hydraulic systems depend on the non-compressibility of fluid. Gas is compressible (or you wouldn’t use it in your tires) and will not push out the brake pads when the lever is pulled. Boiling fluid in the system is called “vapor lock,” and if it happens to you, you can get some braking on a DOT fluid brake by pumping the lever to get home and bleeding the system with new DOT fluid once at home. On a mineral oil brake, you just need to let the brake cool down.
Metal pads deal with heat better and last longer; resin pads give better control (modulation) of wheel speed and wear faster, especially in wet conditions.
To burnish (i.e. “burn in” or “bed in”) new pads, apply one brake at a time firmly and evenly (while the bike is moving, obviously) without letting the brakes get too hot, which can cause glazing of the pads. Bedding in the pads properly reduces squealing problems.
Shimano’s mineral oil is a brake fluid unique to Shimano. Do not use mineral oil made for another brake system, like Magura, because it is not the right viscosity. And for this exact reason, do not use mineral oil from manufacturers other than the brake manufacturer that advertise that their oil works on all mineral-oil brake systems.
The bleed kit for the Stroker line of Hayes hydraulic disc brakes is the same as for the Mag, HFX9, Sole and El Camino brakes, with the exception of the thread-in tip. And instead of just leaving the lever as the highest point the entire time, you now rotate the lever down, up and middle position on the handlebar a few times while squeezing the bottle of fluid attached to the caliper.
Bed in new pads by bringing the speed down from 10mph to 2mph ten times followed by ten times of bringing the sped down from 14mph to 2mph.
Check out SRAM Tech on YouTube.
To free the shaft from the outer leg on the damper side to pull the outer leg casting off of a 20009 Manitou fork, you do not loosen the bolt at the bottom of the leg counterclockwise and tap it with a hammer as with most forks. First, remove the rebound knob: screw the knob in all of the way (clockwise), and remove the screw inside the knob with a 2mm hex key (counterclockwise). Insert an 8mm hex key into the end of the damper shaft and turn it clockwise until it is free of the casting and can be pushed in.
With Mavic mountain or road freehubs, use only a few drops of 10-weight mineral oil on the teeth and pawls. Phil Wood Tenacious Oil is also recommended, but don’t use lighter weight oils than 10W, since they will flow out and leave the mechanism unprotected. Don’t grease the pawls, as it could stick them down, and don’t grease the outer seal, which would attract dirt that could make its way inside the freehub.
The full description of the 2010 Park Tool Tech Summit is posted in my column on www.velonews.com.
Technical writer Lennard Zinn is a frame builder (www.zinncycles.com), a former U.S. national team rider and author of numerous books on bikes and bike maintenance including the pair of successful maintenance guides “Zinn and the Art of Mountain Bike Maintenance” – now available also on DVD, and “Zinn and the Art of Road Bike Maintenance,” as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.”
Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn.
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