Mountain Bike Maintenance

Rotor Cleaning

The most important tool for cleaning rotors is Isopropyl Alcohol (Isopropanol or Rubbing Alcohol are other names for the same thing). I buy it in a 500ml bottle and transfer it into a small ‘dropper’ bottle which lives in my tool box.

** Isopropyl Alcohol is highly flammable and is also harmful to your health **

From Rutgers University Center of Alcohol Studies:

Isopropanol, common rubbing alcohol, is also quite toxic. Small amounts, as little as several ounces, can cause permanent damage to the visual system, and eight ounces is usually lethal. Some alcoholics may consume methanol or isopropyl alcohol, intentionally or unknowingly, with potentially lethal consequences.

Whatever containers you use, store them carefully and keep them well away from children and idiots.

Drip the IsA all around the rotor face…

I use my thumb to spread it about, concentrating on any areas where dirt or contaminates may have built up*. Use a clean, thick cloth to wipe away the fluid, carefully ‘polishing’ it until the surface of the rotor is clean and free from smears. Repeat this process on the flip-side and then return to the first side for a final wipe.

*If you’re finding baked on, black grime on your rotor, it’s possible that there is some brake pad contamination from hydraulic fluid. If there is any kind of oil contaminating your pads; WD40, DOT, mineral, then it’s highly likely that you’ll be able to see black smudges, or streaks, on your rotors. Also check the pads to see if they have a ‘wet’ feel to them. Basically, any oils on the pad/rotor will combine with the dust produced from the pads under braking to create a paste, which then gets deposited onto the rotor or gunks up the pads, or both (more likely). This ‘paste’ is now your braking surface, hence the drastic drop in performance, possibly accompanied by unusual squeaking.

A spill of oil/fluid can usually be washed off with IsA if you catch it straight away. Once you’ve used the brakes with a contaminated pad, as far as I’m concerned the pads are finished and should be replaced. However, if you do a search around the Brake Time forum, you’ll find examples of baking/heating/burning the pads to get the oil out.

Oil/fluid on the rotors can just be wiped away with a cloth and some IsA. If it has got to the ‘black streak’ stage, you can just scrape the marks off with your fingernail, before cleaning it up with the IsA.

Oil/fluid on the rear of the pads may indicate failure of the piston seals or loose bolts/fittings on the caliper. Check all your fittings, wipe the inside of the caliper clean with tissue and cotton buds to get around the pistons, then make sure the rear of each pad is properly cleaned and dried, refit, and check them again after a bit of riding. More oil? Time to investigate a seal change.

It is possible to freshen up your brake pads using a fine-grade sandpaper, I find 180 works well. Remove the pads from the calliper as per the manufacturers’ instructions. Put the sandpaper on a flat surface and, using a circular or figure eight motion sand each pad until the surface is clean and even. After doing this your pads will require bedding in again.

Bedding in is the process whereby the surfaces of the pads and rotor wear away a little until the profiles of each match each other. As the pads are the ’softer’ of the two materials, their surfaces will be carved out to match the profile of the rotor as it rotates, although some microscopic changes will also occur on the rotor surfaces. Once they have bedding into the rotor, the effectiveness of the pads is at its best. Here’s my method for bedding my brakes in…

Refit the pads head outside with a bottle or pint glass of fresh, clean tap water. Get up a head of steam and brake hard. Pour water liberally over the caliper. Pedal off again, this time with the brake applied lightly. As you pedal you’re going to feel the pads bedding in to the rotor. Keep going, pulling the brake gradually harder as you have to pedal harder. Do this for 20-30m and then pour water of the caliper again. Repeat a mix of hard stops, water; brake/pedal, water until your brakes are how you like them. I can get both of my brakes bedded in in under 10mins using this method. They’ll improve further after a little trail time, but at least you’ll have decent braking to begin with.

It’s worthwhile keeping an eye on the interior of the disc brake caliper. It may not be such an issue for cable actuated brakes, but the piston seals on hydraulic brakes will be affected, over time, by the ingress of dirt and brakes dust, especially if you ride often in the wet. You may not even need to remove the caliper, but with the pads out of the way, take a cotton tip around the interior of the caliper, paying special attention to the exposed surface of the piston and the point where the piston and caliper body ‘meet’. A little (very small amount) of brake fluid (DOT or mineral as appropriate) can be used to soften any built up crud. If you find yourself needing to push pistons back fully into the caliper (resetting pads?) it is advisable to wipe the piston first. Clean seals will last way longer than gritty ones and the lever feel of a well maintained brake will always be superior to that of one which is not cared for.

‘V’ or Rim Brake Cleaning

A disadvantage of rim brakes is that one of your braking surfaces is a relatively expensive wheel; the braking surface of the rim will be worn down over time and need replacing. Any foreign objects that get stuck in the pads or are between the rim and pads during braking are going to rapidly decrease the useful life of your wheel. The dirt can’t (shouldn’t!!) be avoided when you’re riding, but wiping your rims whenever possible on the trail is not necessarily a bad habit to have.

Off the trail, try to get dirt from the rim before it dries and use plenty of water to wash it away. I’d use a washing up sponge with a light plastic (not metal!!) scouring pad to wipe the braking surface. The scourer should remove any stuck-on pad residue, but you could use your fingernail to scrape any particularly stubborn streaks. The advantage of a scourer is that it will lightly roughen the braking surface, which can result in improved pad performance. Go around both braking surfaces until they are clean and then dry with a clean, dry cloth. I’d advise against using any cleaning agents (IsA, spirits and the like) as they can make rims ’squeaky’ clean; a step too far, I’m sure you’ll agree!

The simplest way to clean the pads is to unhook the noodle from the brake arm and wipe them with a cloth. Inspect visually first, then run your finger over the surface of the pad to feel out any objects that may have become lodged in the pad. I’ve seen a small stone gouge a trench in a rim in no time at all, so be prepared to stop on the trail if the scraping noise coming from your brakes seems perhaps a little too loud. Use a small screwdriver or blade to pick the grit from your pads.

Rim brake pads can filed to assist them bedding in when new or to freshen up a well used set. With a small enough file, and plenty of care, this can be done with the brakes still on the frame (use a thick cloth to protect the rim). If you’re freshening old pads up, remove the whole brake arm rather than removing the pad separately, thus saving you from having to reset the position of the pad afterwards. It also gives you the opportunity to clean the brake arm assemblies. Work along the length of the pad until the surface is evenly filed.

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