Disc brake pads usually last much longer than V-brake pads. The material in the disc rotor is much harder than the material in the rim, allowing the disc brake pad to be much harder as well. Were you to use the material in the disc brake pad as a rim brake, the rim would wear away in next to no time. The harder material also means that the pad can touch the rotor as the wheel spins without slowing down significantly – so you don’t have to worry about a slight rubbing noise when you spin a wheel with a disc brake.
Make sure you get the right pad for the brake; the fittingsand shapes vary between makes, and between modelsfrom the same make. Take the old ones along to your bike shop for comparison if you’re not sure. Even if you know the make, the shape will vary from model to model and from year to year. After fitting, new pads need to be bedded in – they don’t work properly until you’ve braked a few times. Once you’ve got the new pads in, find somewhere you can ride the bike safely with limited braking power. Ride along slowly, haul on the brakes and bring the bike to a halt. Repeat at increasing speeds, until you’re satisfied. This may take 10 or 20 repetitions.
The pads on mechanical brakes sometimes wear unevenly. The most common design has the cable from the brake lever pull an actuation lever (mechanic’s term for ’lever that does something’), which pushes the outer brake pad onto the rotor. The rotor flexes under the pressure, gets pushed against the other disc pad, then ends up firmly trapped between two pads. This can cause uneven wear, but you must still change both pads at the same time even if one looks more worn than the other. They should be replaced when either of the pads has less than 0.5mm (1/16 inch) of thickness left from any direction. You may need to take them out to check how they’re surviving. If in doubt, follow the procedure for removing them below, and refit them if they have life left. Clean your rotors whenever you fit new pads.
Changing brake pads
Drop the wheel out of the frame. Look at the brake calliper. You’ll see that it has a slot into which the rotor fits. Most often, the pads will pull out in the same direction that you pulled the rotor out of the slot – towards the centre of the wheel. Some will pull out of the top of the brake calliper, away from the centre of the wheel. Have a good look at the calliper before you start and draw a picture if necessary to help you put everything back together. There will be a pad on each side of the rotor, and it will often have little ears or tabs to pull it out. Use these to manipulate the pads, rather than touching the pad surfaces.
Step 1: Often the pads will not pull straight out; they will have some kind of device that stops them from getting rattled out as you ride. This will normally be a pin that goes through the opposite side of the pad, so look on the other side of the calliper for a retaining pin or split pin. (If
necessary, use pliers to bend the ends of the split pins straight.)
Step 2: Pull out split pins, retaining pins or P-clips – keep them safe because you need to fit them back at the end. There may be one or two retaining pins. Split pins need to be bent gently straight with pliers before you can pull them out
Step 3: Gently pull the pads out, either by grabbing the little ears that poke out of the slot, or by pulling on the corners of the pads. If you’re not sure of the correct replacement pads, take the old ones to your bike shop to match them up
Step 4: The pads may have a retaining spring; make a note of its position and orientation, and refit it with the new pads. Take care when fitting the new pads that the arms of the spring sit beside the pads, not over the braking surface. It’s easiest to squash the spring between the pads, then fit both into the slot together, rather than trying to get the pads into the slot one at a time
Step 5: Slide the new pads back into the calliper, pushing them in until the holes in the pad line up with the retaining pin holes in the calliper. Refit the retaining pin or pins, bending over their ends, so that they don’t rattle out. Then pull the pads firmly to make sure they are held securely in place.
Step 6: Refit the wheel, wiggling the rotor back into the gap between pads. You may need to readjust the cable because new pads will be thicker than the old ones. Pick up the bike and spin the wheel. It should spin freely, without binding. However, it’s fine if you can hear the pad rubbing slightly on the rim – this won’t slow you down. If the rotor drags or the brake lever pulls back to the bar without braking, go to the adjustment section.
“New pads need to be bedded in – they don’t work properly until you’ve braked a few times”
- Ensure you have the correct replacement brake pads before you start – they vary between make, model and year of manufacture.
- Most pad set-ups rely on a return spring that sits between the two pads to help them release when you’re finished braking. If you don’t get a new one with the new pads, clean the old one before reusing. Ensure that the side arms of the spring sit beside, not over, the brake pad surface.
- Pads will need replacing when there’s less than 0.5mm (1/16 inch) of brake pad left. Don’t leave it too late – once you wear through to the metal backing, it will tear up the surface of your rotors.
- If there is life left in the old pads, wrap them up and put aside for emergencies.
- You can freshen up the surfaces of dirty pads by cross-hatching them with a clean sanding block. However, once the pads become contaminated with oil, they will need replacing.
- Resin pads are cheaper than sintered, but wear out more quickly. They’re more suitable for commuting than off-road use – on long descents they may overheat, diminishing your braking power. Sintered pads are recommended for off-road use.
- Titanium-backed brake pads are lighter, but also disperse heat buildup more effectively that standard pads.
Keeping pads and rotors clean
Your rotors should be a routine step in your regular bike cleaning-routine – they’ll last longer and stop you better with a bit of care on the braking
surfaces. Indications that attention is overdue include squealing when you apply the brakes and deterioration in your braking performance.
The most common contaminant is stray oil from overzealous chain lubrication – one of the many good arguments for drip application! They’ll also pick up oil from your fingers, from any leaky seals in the brake calliper or from diesel spills on the road. If you suspect anything’s found its way onto your rotors, act swiftly – rotors can be cleaned, but if the contamination spreads to your brake pads, you’re more likely to be looking at replacement.
Recommended cleaning fluids include isopropyl alcohol and dedicated bike brake cleaner. Muc-Off make a goodvalue, effective version. Just don’t be tempted to use car or motorbike disc cleaners, they’ll leave a residue on your rotors. Use a clean cloth or fresh kitchen towel to wipe the rotors.
If you’re still getting a squeal after cleaning the rotors, check they’re securely bolted onto your wheels – loose rotors will vibrate noisily as you brake. In particular, for six-bolt rotors, loosen off all the fixing bolts so you can wiggle the rotor from side to side. You’ll be able to feel that the bolt holes are slightly larger than the bolts, so you can rotate the disc just slightly back and forth as well. To minimize brake squeal, roll the rotor
backwards as far as you can (clockwise as you look at the face of the rotor) before tightening the six fixing bolts in sequence to torque (2-6Nm). This helps reduce the potential for vibration under heavy braking.
Source : BIKE MAINTENANCE TIPS, TRICKS & TECHNIQUES