You should check your cables regularly for corrosion, kinks and damage to the outer casing. Over time, dirt and water creep into the cables. It happens slowly so you hardly notice the brakes are getting harder to pull on and are not releasing properly. Fitting new cables is easy and you will feel the difference instantly.
Cables generally come in either standard or fancy versions. The luxury versions tend to be either lined or protected by a sheath that runs from shifter to brake. Luxury cables can make a significant difference if you ride in very muddy environments, as they stop grit from creeping into the gap between cable and outer casing. However, they are generally much more expensive. All cables come with comprehensive instructions though, so we’ll stick to standard cables here. You can either buy brake-cable sets in a pack, with cable, outer casing and ferrules – Shimano make a good value pack – or you can buy the parts separately. Ferrules are the metal caps that the end of your outer casing sits in. Either way, you’ll need a decent pair of cable-cutters to cut the casing to length; every bike has a different configuration of top tube lengths and cable-stop positions so the casing needs to be cut for each one. The key thing to remember when cutting casing is to make a square cut across the tube so that the end of the casing sits firmly inside the ferrule. Look into the end of the cut casing and make sure there isn’t a stray tang of metal across the hole. This will catch on the cable every time you pull and release the brakes, making your brakes feel sluggish. Use the sharp point of a knife to open out the end of the white lining that runs through the casing as it gets squashed shut as you cut the casing. Occasionally, you come across cheap, unlined casing. Don’t fit this to your bike – it will feel terrible. It’s fine for lawnmowers, but the extra money you spend on proper lined casing will make your brakes feel at least twice as good. You’ll notice throughout this text that we’re keen on ferrules. They cost almost nothing, protect the ends of your casing from splaying out and make your brakes feel crisp. Yet they are often treated as an optional extravagance. The only place you won’t usually need a ferrule is the end of the section of casing that fits into the V-brake noodle. The noodle has its own built-in ferrule.
Fitting new brake cable to a flatbar lever
Before you start taking things apart, have a good look at how the cable is currently set up because you need to recreate that later with the new cable. Snip the cable end off the old cable and undo the cable pinch bolt. Unthread the old cable from the brake noodle and outer casing, leaving the casing in place. When you get back to the lever, have a good look at how the cable fits into it. It helps to pull the lever back toward the bars, to look up at it from below.
Step 1 : Turn the lockring on the barrel-adjuster, and then the barrel-adjuster itself, so that the slots on both the barrel and the lockring line up with the slot on the body of the brake lever. Then pull the cable gently outward, or down, to release it.
Step 2 : The nest, where the cable nipple sits, normally has a key-shaped hole so the nipple cannot pop out when you’re braking. The most common fitting has a pivoted nest riveted to the lever blade, with a slot in either the front or the underside of the lever. Wiggle the cable so the nipple lines up with part of the hole that it can pass through, and pop it out. You may have to twist the cable so the end of the barrel lines up with the key hole.
Step 3 : Some Shimano levers use a variation where the nipple is trapped behind a lip halfway along the lever blade. Once again, line up the slots on the lockring and barrel-adjuster with the slot on the body of the cable. You will need to flick open the plastic cover on the back of the lever blade, then push the cable towards the outer end of the lever. Once there’s a bit of slack, you should be able to wriggle the cable out from behind the lip.
Replacing outer casing
Clean out the brake lever; in particular, wipe dirt from the nipple nest. Remove each section of outer casing in turn. Measure and cut new sections to fit. Take care when cutting the sections of outer casing. It’s important that the ends are cut square and that you don’t leave a tang hanging across the opening. If the casing lining has been squashed where you cut it, use the point of a sharp knife to open it out again. Fit a ferrule on each end of each section, except the brake unit end of the final section because the noodle will usually have a built-in ferrule. Occasionally these are bigger than normal, so if the casing is floppy in the end of the noodle, try fitting a ferrule. If you can fit one in, you need one. The ferrules protect the end of the casing from splaying out and keep braking crisp. If there is no old casing to measure up against, you have to decide how long each section of casing should be. Ideally, sections should be as short as possible without binding. Make sure the handlebars and suspension can go through their full range of movement without pulling on the cable. Sections of casing should approach cable stops so that they are already lined up with the cable stop. Sharp curves cause sluggish brake performance. Refit the nipple in the brake lever, using the reverse process you needed to get it out. Line up the barrel-adjuster slots and tuck the cable back into the barreladjuster, then give it a quarter-turn to trap the cable. It’s important not to let the new cable drag on the floor and pick up dirt as you fit it. Slide the cable through each section of outer casing in turn, with a drop of oil on portions of the cable that will end up inside casing.
“It’s fine for lawnmowers, but the extra money you spend on proper lined casing will make your brakes feel at least twice as good”
Step 4 : When you get to the final section, feel the cable through the casing, then through the noodle. Ensure the section of cable inside the noodle has a little drop of oil. Fit the noodle into the key-shaped hole in the brake unit. Make sure it’s lodged securely, with the entire nose of the noodle sticking out of the hanger. Slide the black rubber boot over the cable and push it firmly onto the nose of the noodle. Pass the brake cable behind the pinch bolt.
Step 5 : The cable normally clamps on above the bolt, but there will be a groove in the unit where you put the cable. Put it there. Pull cable through, so there is a gap of 2–3mm (around 1⁄8 inch) between brake blocks and rim. Steadying the cable with one hand, tighten the clamp bolt with the other. Leave about 5cm (2 inches) of exposed cable, cut off the excess and crimp on a cable end; i.e. ’squash it with pliers’. Tuck the loose end behind the brake unit.
Step 6 : Test the brake; pull the lever hard twice. The cable might give slightly. Ideally, the brake should lock on when the lever is halfway to the handlebar. Use the barrel-adjuster to fine-tune; undo the lockring and turn it twice, away from the brake lever body. If the lever pulls too far, turn the top of the adjuster toward the handlebars. Do a couple of turns and retest. If the blocks rub on the rim, turn the top of the adjuster away from the handlebar.
If you run out of adjustment on the barrel-adjuster (either it’s adjusted so it jams on the brake lever body, or it’s at risk of falling off), go back to the cable clamp bolt, undo it, pull through or release a bit of cable and retighten. Then go back to the barrel-adjuster and make fine adjustments. Pull firmly on the brake lever again and check that it locks the wheel when it’s halfway to the bar. Make sure that the brake blocks don’t rub on the rims as the wheel turns. Check that every bolt is tight. You’re done.
People are often confused by barrel-adjusters. They’re a common feature of cable-operated brakes and are used to adjust the indexing on derailleurs as well so it’s worth getting you head around how they work. The barrel-adjuster on your brake lever is easiest to deal with because you can see it all. The barreladjuster acts like a cable stop, holding the casing still, while allowing the cable to pass freely through a hole in the middle. Since the barrel-adjuster is threaded, whenever you turn it, it moves further in or out of the body of the brake lever. If you turn it so that it winds out of the brake lever, more of the barrel-adjuster thread is visible. The cable inside has to travel this extra distance between the nipple, where it lodges in the lever, and the bolt that it’s clamped to at the other end. This increases the tension in the cable, drawing the brake blocks closer to the rim. The lockring serves only to stop the barrel-adjuster rattling loose, so it is wound finger-tight against the body of the lever when you’ve finished adjusting.
Source : BIKE MAINTENANCE TIPS, TRICKS & TECHNIQUES