Bicycle Mechanics - BB7 tri-align washers rubbing. Help!
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11-25-08, 11:47 AM
I'm setting up some Avid BB7s on a surly big dummy. The discs are mounted to phil wood hubs. Unfortunately, I'm running into a problem with the front brake. Following proper procedure, the tri-align washers on the bottom hit the rotor arms. By using a wedge while I set the pivot, I was able to get it to not rub, but the clearance is so tight that when you put extra lateral force while riding the bike uphill, they hit. It looks like the adaptor is running too close to the disc, so much so that it causes the caliper to run too close to the disc. I have run into this before with other brakes. Have you? Any solutions? I have already measured the hub, which runs at 101.5 mm, same as the dropouts.
11-25-08, 02:44 PM
set them up and then grind or file them down
11-25-08, 06:43 PM
Good suggestion. The only problem is, when properly set up, I'd have to take out about 1 mm or more to make it work. Yikes! The other solution is grinding off a layer from the mounting bracket, but that is also risky as it compromises the aluminum's integrity.
Is this the result of a slightly misaligned bracket brazed to the frame? The only way to tell, I guess, is to mount a different wheel, and then a different caliper, to see if the problem persists.
11-27-08, 12:52 AM
Can the inner brake pad be 'backed off' so that it has more clearance between it and the disc rotor?
If it can then you might be able to adjust the calliper by moving it outwards away from the rotor to give you more clearance.
A washer put on the axle so that it sits between the inside of the fork end and the hub would give some clearance also.
11-27-08, 08:25 AM
Call around and find a shop that offers disc tab facing, or if you have a spare $125 lying around...buy the tool (http://www.parktool.com/products/detail.asp?cat=14&item=DT%2D1).
After having the same frustrating issue you're dealing with many, many times (especially on Giant and Surly products for some reason) I purchased one for our shop and use it regularly. On high end bikes I face the tabs for firmer contact between the caliper and frame to reduce squealing and increase power, even if no alignment issue exists. On bikes with no tri-align feature, it sure beats playing with shims. If like your bike the tabs are too close to the rotor, removing material can be the only way to fix the issue.
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