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Dirt Rag Fresh Dirt
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2.9.2007
Microbytes: Disc Brake Alignment and the Tools to Get 'R Done
By: Brad Quartuccio
It is incredibly important for your disc brake caliper and the disc rotor itself to be in alignment with each other. The brakes pads should contact the disc perfectly flat, and each side should touch at the same time, for consistent power and minimal squeal. Its all about the alignment.
Sometimes this is easier said than done though. The included shims and/or conical washers may not be enough to get particular bike's caliper and rotor in plane. Excess paint, misaligned tabs and variances in manufacturing specs may only add up to a millimeter or two, but sometimes that's all it takes to make loud, grabby brakes into consistent, silent ones. Wheel swaps and brake induced heat make it all the more complicated.
The first "tool" is also the simplest, and more of a diagnostic one. Just a yellow Post-It Note, or any other piece of lightly colored paper. Whatever you have around in the scrap bin or otherwise will do. Holding it behind the rotor allows you to easily see the rotor and pads, and the space in between them. Squeeze the lever and see if your disc pistons move independently, or if one is a bit sticky. Visual feedback on adjustments is key, and this simple tip can make it much clearer.
Next up are Disc Shims from Syntace (www.syntace.com). About $20 buys you the set of eight .2mm shims for under your disc rotor, between it and the hub. These are easier to use than a stack of brake-tab shims to get your rotor and caliper positioned correctly with one another. They can also make wheel changes easier between multiple sets by allowing you to make the rotor fall in the same spot in the caliper on each set. Definitely a good idea that needs to get some airtime.
With International Standard (IS) disc tabs it is imperative that the faces of the tabs are in the same place as each other. Sometimes the paint is visibly thick, or the tabs not aligned just right. Magura (www.magurausa.com) makes the $300 Gnann-o-mat disc brake optimizer. It's similar to a bottom bracket or headset facing tool, and is more of a shop than consumer item. But with it you can make sure that an IS tab is in proper alignment in respect to the rear axle, making setup a breeze. If you've tried a bunch of solutions to no avail, see if a local shop has one of these, or stop by the Magura truck at a race and ask real nice. Or maybe nudge your Richy Rich riding buddy into believe he needs one.
Sometimes its even the disc itself that is warped, either from banging it on rocks or just the heat of a (literally) smokin' downhill. Paul Morningstar (www.morningstartools.com) sells his Drumstix to help get those rotors straight again. The set of three tools goes for $27 – the two outside levers stabilize the disc with the middle one straightens just the bent section. Have a drink when you're done with the included opener.
Well, that covers some of the most common disc brake problems and solutions. There are plenty of other potential disc brake problems out there. Those will have to wait for a future Microbyte.
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