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need help - newly installed brake pads do not align with rims

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need help - newly installed brake pads do not align with rims

Old 08-16-14, 11:23 PM
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totalnewbie
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need help - newly installed brake pads do not align with rims

Tried replacing brake pads for the first time - Shimano Tiagra Caliper on road bike. Unscrewed the small screws that held the pads in place, slid them out and slide in the new ones. Tighten the screw. Then I noticed when I squeezed the brake lever tight, the pads are not perfectly parallel to the rim. When seen from above, I can see the back side of the pad touching the rim, then hairlines towards the front with a <1mm gap. the brake pad is not fully engaged with the rim.

I checked to see whether the brake pad was slide in correctly. It seems so since I can see the interlocking hook between the back side of the pad/shoe locking together correctly. I tried squeezing the brake tight against the rim before I tightened the single screw that holds the shoe in place. But when I release the brake lever, the shoe "bounces" back into the non-parallel condition. I also tried adjusting the brake cable length. Nothing helps. The brake shoes on both sides have the same symptom. This happens only on the rear brakes, the front seems OK.

Aside from the screw that holds the shoe in place, I don't see any adjustment I could make to modify the "tilt" (what is the correct term to describe this?) Should I be concerned? Or should I just wait until the pad wear out to such a point that the surface is parallel to the rim?
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Old 08-17-14, 12:35 AM
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Originally Posted by totalnewbie View Post
Aside from the screw that holds the shoe in place, I don't see any adjustment I could make to modify the "tilt" (what is the correct term to describe this?) Should I be concerned? Or should I just wait until the pad wear out to such a point that the surface is parallel to the rim?
Tilt---might that be "toe-in"? That's where the leading end of the pad/shoe is closer to the rim than the rear/trailing end. Not a lot, a lot of folks use a business card as a feeler gauge to set the distance. I haven't searched, or personally used, your specific calipers----do they not have this adjustment? This would not be where the pad slides into the holder but where the whole shoe assembly screws to the caliper arms.
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Old 08-17-14, 12:54 AM
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Loosen the screw that holds the brake pad holder to the caliper arm. You may find the holder can then be adjusted. In most cases there is a domed washer that allows the holder's angle to be changed. Adjust so that when the front end (tip, or toe) of the pad touches the rim, there is a slight gap between the back end (tail, or heel) of the pad and the rim. That is called "toe in". Then tighten to screw to hold the pad in that position. Make sure the pad doesn't touch the sidewall of the tire. With older brakes, you used to have to bend the caliper arm to achieve toe-in. Now almost all modern brake pad holders are adjustable.
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Old 08-17-14, 07:44 AM
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Even with slip-in replaceable pad new pads sometimes require minor alignment adjustment. As the old pads wore down they conformed to the rim or were never perfectly aligned when installed so the new pads need a bit of realignment.
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Old 08-17-14, 09:04 AM
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Some pads/shoes don't have provision to adjust toe in, no ball and socket between the shoe and the caliper arm. It's easy to get shoes w/ pads that do have this adjustability. Andy.
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Old 08-17-14, 05:38 PM
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i took the caliper/brake shoe apart. There are two washers but both of them are flat so there does not seem to have any way to adjust the "toe-in".
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Old 08-17-14, 06:13 PM
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Originally Posted by totalnewbie View Post
i took the caliper/brake shoe apart. There are two washers but both of them are flat so there does not seem to have any way to adjust the "toe-in".
If you don't mind the minor expense, replace the stock holders with Kool Stop "Dura Type" holders and pad sets. The Kool Stop holders have the concave washers needed to adjust the pads in any preferred alignment with the rims.

Get these: Kool Stop International - High Performance Bicycle Brake Pads Since 1977 After that, all you will need are the inserts when the pads wear out.
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Old 08-18-14, 03:43 AM
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thank you. I will look into that. though I am still perplexed why my stock tiagra brake pad holder does not provide a means to adjust the brake pad, it seems like such a basic safety need.
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Old 08-18-14, 05:55 AM
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Originally Posted by totalnewbie View Post
thank you. I will look into that. though I am still perplexed why my stock tiagra brake pad holder does not provide a means to adjust the brake pad, it seems like such a basic safety need.
Toe-in is not a safety feature, it is mainly to allow the pads to remain quiet when the brakes are applied.
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Old 08-18-14, 07:37 AM
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still curious: why is brake pad alignment (or toe-in as you referred to) not a safety thing? If only my rear 20% of the brake pad is engaged with the rim when the lever are pressed, doesn't that mean my brake has only 20% of stopping power, thus leads to a less safe situation?
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Old 08-18-14, 07:44 AM
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Originally Posted by totalnewbie View Post
still curious: why is brake pad alignment (or toe-in as you referred to) not a safety thing? If only my rear 20% of the brake pad is engaged with the rim when the lever are pressed, doesn't that mean my brake has only 20% of stopping power, thus leads to a less safe situation?
The amount of friction generated is proportional to the force applied and has no relationship to the surface area. For a given lever force, otherwise identical pads of various lengths will provide identical stopping power.

The concave/convex washers that allow toe-in adjustment are a relatively new thing. In theory, the hole in the fork is on the same plane as the rim, so a brake caliper made correctly with the shoes aligned parallel to the mounting bolt would also be parallel to the rim. That's theory, but nothing is perfect, so the standard remedy is to use a wrench and gently tweak the brake arm to square things up. The tweak option isn't possible for canti brakes because the arms are too short.

Lastly, no matter what you do, the brake will establish it's own wear pattern, and the shoes will end up wearing roughly parallel, since the areas touching will wear faster than those not. I said roughly parallel because the brake flexes and twists under load so the rear of shoes wears faster than the front.

In your shoes, I'd leave things alone if the shoes are close to parallel
, but not perfect, and let wear sort things out. One test for whether good enough is good enough is to note the amount of force needed to press the shoes flat. If it's less than what you normally use to top it's fine.
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Old 08-18-14, 08:18 AM
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ok, i will take your advice for now... or maybe i will take a wrench to tweak the wheel rim so it is parallel to my brake pad, if the caliper arms won't budge.
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Old 08-18-14, 08:40 AM
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You cannot modify the wheel rim.
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Old 08-18-14, 08:41 AM
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Originally Posted by jyl View Post
You cannot modify the wheel rim.
I suspect that the problem is probably with the calibration of your irony detector.
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Old 08-18-14, 09:06 AM
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If you do bend them where they are parallel to the rim and they start squealing you will know they need to be bent back to where they were. I always toe mine in slightly.
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Old 08-18-14, 09:13 AM
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Originally Posted by FBinNY View Post
I suspect that the problem is probably with the calibration of your irony detector.
I have been reading too many Stuntex threads.
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Old 08-18-14, 10:42 AM
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Originally Posted by jyl View Post
I have been reading too many Stuntex threads.
I figured that his problem was related to why he chose that name, and gave up on him long ago.

They're not even worth following for entertainment value.
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