In many cases replacing breaking system components is the best course of action but there are occasions when it is possible to repair or service certain pats of the braking system instead. Below we attempt to differentiate the two:
Lubing a cable is often a good idea and can help to prolong its life – a tired and old cable will appear dirty and therefore probably lost its galvanised sheen. This said however, if you find that you’ve applied plenty of lube and that the improvement of the cable performance is not noticably better, it is probably time to replace that cable.
WORKSHOP TIP: It is important to lube and replace cables regularly – i.e. cables should be lubed monthly and replaced at the bike’s three monthly service, or at the very most six monthly intervals (if the bike has been well looked after and the cables regularly lubed.) All cables have a service life – once the cable reaches the end of its life it will snap. Usually this happens next to the barrel end and results in total braking failure.
If the cable is frayed you must also replace it as nothing can be done to repair it in any way.
Brake Blocks and Discs
Classically, brake blocks are replaced when you can no longer see the groove on the pad. Brake pads need replacing often as they wear so fast.
With discs, the general rule of thumb is to replace them when they have 1/2mm of pad left on them. Experienced mechanics can distinguish this by simply holding the wheel up to a light source, pulling the brake lever and peering into the disk caliper to test for wear. We would recommend taking the disk out however and having a good look for yourself.
WORKSHOP TIP: It is very dangerous to let the pad wear down to metal as, when it rubs against the rim which is also a metal surface, grooves are worn in the braking surface. Over time, this can make the rim slightly concave, and the rim may collapse under pressure while being ridden. Rims will often have an indicator in the braking surface to show when it needs replacement – for example many rims have coloured dots in them, and when these dots disappear you know it is time for replacement.
If the brake studs become very rusty you will need to replace them. The problem with this is that some bikes (i.e. BMX forks) do not have replaceable studs and the whole fork would need to be replaced. It is possible to replace the studs on cantilever brakes.
Likewise, many older cantilever brake forks were manufactured with 8mm threads of the brake studs, whereas most modern machines now take 10mm studs. It can be difficult to find the replacement for the older technology and may result in you having to also replace the whole fork.
Generally, you would not attempt to repair high end racing bike brake calipers or disk brake calipers. This is because, if you dismantle them, they are made up of many different parts and are very complicated to put back together. Also, the spring tension in them is often machine set and impossible to reset back by hand. Replace these calipers if you assess they are a part of the braking problem.
With other types of brakes however such as Cantilever, V Brakes and BMX U brakes, you can service the calipers first. If you do this however and still find that there is very little braking power, you are probably going to have to replace the caliper anyway. Most bicycle workshops would replace the caliper as a matter of course if they thought it was playing up.
WORKSHOP TIP: Many cheap bikes are fitted with plastic calipers. Plastic is a material that will eventually bow and buckle under the constant pressure of the cable. You are much better upgrading such a caliper when you can – it is really a false economy as these components make the bike cheaper, but they do not stand the test of time.
It is possible to true a warped rotor as discussed in the servicing task. However, when a rotor is well and truly warped into an S shape, or simply it is taking so much time to tinker with to get right that it would be a more economical solution to simply replace it, then it is recommended that you just fit a new one.
Truing rotors can be a very fiddly task and, unfortunately, they often come straight out of the packet slightly bent from transit. A workshop mechanic can often find themselves trying to remedy this problem.
Obviously if the cable housing is ripped in any way it will not be able to offer the protective passage that the cable needs in able to do its job properly – it may get snagged or impede the cable in some way.
Likewise, if the cable housing becomes clogged with dirt and old grease it will also prevent the cable from moving freely. It is not an expensive part to replace and we would recommend that you do so at a bike’s 3 monthly service. See Cable Housing Preparation and Measuring the Cable Housing.
If a noodle is bent or broken in any way it will kink the cable inside. Cables need to travel in as straight a line as possible to the brake and if it is caught on the inisde of the noodle then the noodle must be replaced also.