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Rear brake modulation is terrible after component swap to new frame.

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Rear brake modulation is terrible after component swap to new frame.

Old 11-12-17, 11:45 PM
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willydstyle
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Rear brake modulation is terrible after component swap to new frame.

I switched all of my components, including wheels, to a new frame. This involved installing fresh cables and housing. The brakes are new manufacture dia compe centerpulls. The brake levers are a new manufacture IRD aero model.

I think the new frame may have originally been meant for 27" wheels because I had to move the brake pads down in the brake arms a few mm, but other than that these are the same brakes on the same with the same levers, and this braking system worked flawlessly on the previous build.

The problem is that the rear brake modulation is basically non-existent. I'll pull the lever, and I'll feel the brake contact the rim, but then suddenly the brakes will be full power. I have to brake incredibly carefully not to lock up the rear wheel. The front brake is performing up to expectations. Does anyone have any clue about what might be causing this?
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Old 11-12-17, 11:59 PM
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dabac
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Has the toe-in of the pads changed?
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Old 11-13-17, 12:03 AM
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Separate the various parts of the brake system and look at each's function. Move the lever without the cable attached. Does it move freely? Next is to pull/push the cable through the casing using your hands at each end to hold the inner cable. Does it slide freely? Next is the caliper, squeeze it together and wiggle the arms WRT the backing yoke. Do the arms move freely in only the plane of rotation to the rim or do they also slop fore and aft?


Your description usually means the caliper arms have enough slop in their pivots so as the pads contact the rim and the rim's rotation acts on the pads the arms rock with the rim a bit. This movement of the caliper arms/pads can cause sudden changes to the "power" of the system. But the condition of the cables can also have some of this effect. If a cable casing end has a casing coil not well cut/finished end it can cause a snag on the inner cable. This will make the inner cable move in bits and spirts as it's weavings snag of the casing burr. Andy.
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Old 11-13-17, 06:46 AM
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Make certain that the brake pads have not developed a lip at the bottom (due to being set too low) which can catch under the rim, causing the symptoms you describe. The lip can be easily removed with a utility knife and cleaned up with a file.
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