I've spent a number of hours 'deep cleaning' my Giant Defy 4 road bike and it looks really good.... with the exception of the rust which is visible on the brake caliber screws/bolts. Are they replaceable? What size? Where can I buy them? Or do I need to replace the calipers?
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1i can think of a couple of different bolts associated with a couple of different types of brake calipers. please include a photo.– Paul HCommented Feb 15 at 0:09
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2 Answers
Below you'll find an Exploded View diagram of a BR-R2000, the Claris caliper brake. Note that the bolts, numbered 1, 8, 9 and 12 are pertinent to the caliper itself, while number 11 is a bolt for the brake pad. By each number is a description of the part and, in the case of a bolt, the metric size and length are given. A well-equipped hardware or home store should have a variety of metric bolts in their bolt bins.
It's likely you won't find an exact match to the Shimano bolts at a store. Details such as the shape of the head, the presence and length of a shoulder (non-threaded area of the bolt between the head and the threads. Number 1 is such a bolt), and length may differ from the original part. Typically one can get a bolt that differed in these parameters to work (ie: one can cut or grind a bolt thats too long). However, one aspect of the replacement bolt that must be the same in addition to the diameter (the M #) is the thread pitch, or the distance in millimeters between thread peaks (or valleys). This number is not given in the Exploded View, but will have to match the original bolt for a replacement to work. There are generally two pitch standards per bolt diameter, a coarse standard and a fine standard. The coarse standard is most commonly used and typically what is found both in use on the bike and available at a hardware store. Commonly used diameters of M5 and M6 bolts often times have BOTH the coarse standard and fine standard pitches available in bolt bins I have experience with.
A bolt with an incorrect pitch will usually start to thread into the hole one to two turns but then meets resistance as the threads become misaligned. Continuing to thread the bolt against the resistance will mess up both male and female threads, damaging the caliper.
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The pivot bolt might be tricky, but the rest should all be replaceable with stainless. You might need to get something a mm or two longer, and be prepared to grind or file it down to length. The pivot bolt looks to have a very low head and a shoulder. While I know of a supplier of both, I'd hesitate to recommend buying anything without the parts in my hand and my vernier calipers in the other.– Chris HCommented Feb 15 at 15:10
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The reason the pitch isn't stated is almost certainly because it's standard (i.e. coarse) - M4x0.7, M5x0.8, and M6x1. I know that's the case for the equivalent of items 1, 8, and 12 on other shimano assemblies. Even they don't use more expensive uncommon pitches without good reason.– Chris HCommented Feb 15 at 15:13
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1@Chris H Yes, exactly. I mused about trying to include this info within my answer where I mention the equivalent pitch requirement. I have found that standard pitches are typically used. I'm going to edit my answer as this is a very relevant point when searching for a substitute bolt.– JeffCommented Feb 18 at 20:18
Surface rust is generally not an issue, it is merely a visual blemish.
If the rust was deeper than a light surface dusting then that can be an issue for safety.
To clean surface rust you can try
- Wire wheel or wire brush to knock off the rust. A small brass bristle tip in a rotary tool might be enough. Then add a thin smear of sealant on the outside - I have a recent preference for Lanocote, but keep your braking surfaces and pads absolutely clean.
- Rust treatment products that convert the red iron-oxide rust into something more stable, like iron-phosphorous molecules which are black and inert.
- Outright replacement of bolts, but be sure to get the same thread and diameter, and the metallurgy of the bolt should be no-weaker than what was there (ie avoid the cheap bolts in a box-store) The bolt's head dimensions and driver also have to fit. Be mindful of the length too - neither too long nor too short.
You don't need to replace the calipers, though do check pads for wear and replace those if needed.
