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Old 02-24-06, 04:27 PM   #1
thomasbien
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Centering 105 brakes...

I am building up a bike for my wife and last night I began brake and brake cable installation. I installed Shimano 105 dual pivot brakes onto the frame and fork, but I am curious about centering the brakes over the rims.

Front wheel as an example: I snug the nut holding the front brake, eyeball the spacing on between left and right brake pads and rim, and tighten the nut. Then I installed the front brake housing and cable. When I turn the handlebars 90 degrees in each direction, to see if I have a proper length of housing, the force of the brake housing pushes the brakes out of center. Thinking that I do not have the nut attaching the brakes to the fork tight enough I get out the torque wrench and set it to 87 in-lbs (Shimano specs 69 - 87 in-lbs) and find that I have already tightened the nut past 87 in-lbs.

It seems to me that a lock washer or even rubber washer between the brake assembly and mounting point on the fork would go a long way in preventing the brakes from spinning so easily but no such pieces came with the brakes.

What am I missing here? Suggestions?

Thanks.
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Old 02-24-06, 05:01 PM   #2
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Your housing should never get tight enough to move the brake caliper off center. Apparently you cut the housings and cables too short.

The recommended torque to hold the calipers is more than enough under normal circumstances amd you do not need, or want, lockwashers or any other type. The problem is housing length and I'm afraid you are going to have to redo them.
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Old 02-24-06, 05:41 PM   #3
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For fine-tuning the centering of the pads against the rim, there is a hex screw above the caliper arm pivot point. In the image, it's above the right brake pad, & hex screw head is hidden in the recessed opening that is still part of the left caliper arm. Makes sense?
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Old 02-24-06, 05:56 PM   #4
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The nut that tightens your talking about tightens the brake caliper to the fork. On some Shimano Dual Pivot brake calipers there is a knurled collar that sits on the main pivot shaft that the springs are mounted to that has a set screw in it to holds it's rotational orientation on the shaft. It sounds as though that set screw is loose.

Your caliper should not rotate (un-center) easily by hand when the mounting anchor nut has been tightened to the torque you have mentioned.

It is hard to tell without pictures or specific model info, but basically there are adjustments on these brakes to change how much play is in the arms on the front half. Set too loose in some models and they can actually rotate.

After tightening the set screw you should be able to set the rough centering by hand or wrench on the main mounting anchor nut and then do fine centering adjustments with the small bolt though the top of the one pivot arm.

When properly mounted the caliper body should not be able to rotate on the mounting shaft unless intentionally forcing it (~Kinda Hard) by hand. Free movement? - means loose adjustment along main shaft.

Then worry about the housings.
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Old 02-24-06, 06:42 PM   #5
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Once off-centered, use a cone wrench to hold and re-center the caliper and re-torque. Using a cone wrench makes this centering business so easy....
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Old 02-24-06, 06:58 PM   #6
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With these new calipers from Shimano, one cannot use cone wrenches. Campy's are still OK though.
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Old 02-24-06, 07:00 PM   #7
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Quote:
Originally Posted by Jeprox
With these new calipers from Shimano, one cannot use cone wrenches. Campy's are still OK though.
Oops......thanks....I learn something new everyday..
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Old 02-24-06, 08:17 PM   #8
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Quote:
Originally Posted by The Fixer
Once off-centered, use a cone wrench to hold and re-center the caliper and re-torque. Using a cone wrench makes this centering business so easy....
That advice was correct for the former single pivot design. DP brakes are easily centered by hand and no tools are needed.
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Old 02-24-06, 10:58 PM   #9
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Thanks for the replies and helpful suggestions.

I do not think the housings are too short, but I have attached pictures of the front and rear arrangements to confirm this. The front seems to approximate the routing of my bike that was setup by the LBS. The rear looks different due to the fact that the frame is smaller. I didn't think it should be any shorter else the housing would enter the brake at an angle. Should I adjust the length of the front or rear housings?

I know about the adjustment screw on the top of the brake. I have used it to tweak the clearance between pads and rim. Then when I squeeze the brake lever and let go the whole brake seems to turn on the bolt and no longer be centered.

Psimet2001: I do not see an obvious set screw as you have described. These are new (presumably 2005) Shimano 105 brakes. Do you know if there is indeed such a set screw on this brake model?
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Old 02-24-06, 11:11 PM   #10
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Quote:
Originally Posted by thomasbien
Psimet2001: I do not see an obvious set screw as you have described. These are new (presumably 2005) Shimano 105 brakes. Do you know if there is indeed such a set screw on this brake model?
Yeah, I apologize for being vauge earlier. Here's the deal: Shimano Dual Pivot calipers are comprised of what I'll call 3 arms. These three arms are the two on the "outside" which hold the brake pads, and the one shorty closest to the fork that hold the spring.

If you look underneath the small pivot arm, in the center, there is a recessed 2mm set screw. If this is loose then the entire 3 arm assembly is free'er to rotate around the center shaft of the assembly.

I just went down and loosed mine to duplicate your results. Tighten that recessed set screw. This should fix your problem.

Let me know if you have trouble finding it, or if it doesn't fix your problem.

Hope this helps.
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Old 02-25-06, 07:37 AM   #11
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Uh, why are you turning the handlebars 90 degrees in each direction relative to the fork? Once the stem is tightened down, the handlebars will never move relative to the fork and front brake, and therefore the cable housing will never force the brake one way or another.
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Old 02-25-06, 12:52 PM   #12
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If you look underneath the small pivot arm, in the center, there is a recessed 2mm set screw. If this is loose then the entire 3 arm assembly is free'er to rotate around the center shaft of the assembly.
I think you have the right answer. I'll bet the set screw is loose.

Looking at the pictures, the front brake cable seems to be routed about right so it shouldn't pull on anything as the bars are rotated and the caliper arm shouldn't hit the frame.
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Old 02-25-06, 03:34 PM   #13
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Thank you Psimet2001, I tightened that set screw you described and the brake does not pivot anymore. I did not even know about that screw, the installation instructions from Shimano do not mention it.

Thanks again!
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Old 02-25-06, 04:10 PM   #14
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Quote:
Originally Posted by thomasbien
Thank you Psimet2001, I tightened that set screw you described and the brake does not pivot anymore. I did not even know about that screw, the installation instructions from Shimano do not mention it. Thanks again!
Glad it solved the problem. The reason Shimano's instructions don't mention it is that it's not supposed to be loose ever unless you are completely disassembling the brakes so it's not an installation item. I don't know how it got loose on your brakes but it must have been a fluke.
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Old 08-17-12, 11:46 PM   #15
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I know I'm digging up an OLD post, but I used the search to find it rather than posting a new topic that's been covered before. I've been dealing with this same issue for a long time but it never bothered me enough to do anything about it. Today I got caught in a very heavy rainstorm so I put the bike up on the stand and gave it good dry off and clean and lubing. Obviously it was soaking wet and covered with sand from all the puddles, so it was urgent. (An air compressor and blow gun are a huge help in this area) When I was spinning the chain to clean it I was once again reminded of the off center brake issue (rear, in this case) I was convinced that my cable housing was too long because if I pulled it out of the stop it would be more centered, it seemed the cable housing was pushing the brake down on one side due to its length.
Then I came back in and re-read this thread and saw that if the brake is mounted tightly enough it should NOT move freely, side to side; that you should be able to put it in a position and it should pretty much stay there. I wondered if I had even tried that. I went out and tried pushing it to one side and saw that it very easily moved and certainly did not stay there, in fact it was kind of wiggling around a little. I went to the back side of the brake to the 5mm allen head mounting bolt and tried to see if it had room to tighten, and it sure did. Not that I could get my hand in there, but I would call it barely hand tight. I was able to tighten it up a good full turn, almost. Now, I was able to center the brake, even with the cable housing engaged in the stop. I think I had the spread on the caliper artificially wide to accommodate for this offset to try to reduce the brake dragging, now I should be able to tighten that up a bit and have a shorter throw on the brake lever, I'm pretty pleased.
Again, I'm sorry to dig up an old thread but I think it has some very useful information and I think other people may find it useful. I'm actually glad I got stuck in that storm because now my bike is in better shape than it was before, and I'm glad I finally joined this forum. I try to do any bike repairs and upgrades I can handle myself because I love knowing how things work and when you're out on the road and something breaks it sure is nice to be able to fix it yourself, and continue on instead of having to call a "tow truck". Tomorrow I'm going to attempt my first bottom bracket job...
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