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5 common problems on disc brakes - sorted

 
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mikethebike



Joined: 23 Mar 2015
Posts: 176
Location: England

PostPosted: Mon Mar 26, 2018 5:29 pm    Post subject: 5 common problems on disc brakes - sorted Reply with quote

Disc brakes have a hard time on your bike. They work on huge pressures, are exposed to some extreme heat at times, and all together have a very important job of controlling your speed and stopping you on a penny if needs must.

So it is not that surprising that they need a little TLC from time to time so that you can make sure that they work perfectly.

Before you carry on please make sure that your disc mounts are properly faced as alining your brakes will be very difficult otherwise. If you are not sure please get your bike checked by your local bike shop.

We have put together a simple guide of the basics that should help your brakes to run perfectly. All you need (besides this guide) is a few simple tools and approx. 15-20 mins time.

One of the most common issues with a disc brake is a sticky piston. This can cause uneven piston movement and abnormal pad wear, which can then lead to poor stopping performance and a spongy lever feel. Fortunately, by simply extending and lubing the stubborn piston, you can free it up to regain even movement.

Rubbing is another problem which disc brakes have. This can be either constant, where the calliper has been misaligned and the pads are continually contacting the disc, or periodic, which is usually caused by a bent rotor. Ensuring your pistons are moving freely and evenly will allow you to best align the calliper on the rotor, but a properly bent rotor may require more drastic action.

Brake squeal is often caused by contamination or glazed pads. Contaminants come from oils and other liquids that may have been accidentally spilled on the calliper. Glazed pads occur when the brakes get too hot, and the top surface of the pad material becomes shiny and loses its bite.

NOTE: For further details on how to change your brake pads (based on the Shimano Deore XT example) please click here.



To sort out these 5 common brake issues you will need the following tools: Adjustable spanner, multi-tool, allen keys, strong plastic lever (possibly sturdy tyre lever), possibly new disc brake pads, sandpaper, cleaning products.



UNEVEN PISTON MOVEMENT:
1.) Remove wheel and brake pads. Put the pads somewhere clean, well away from any contaminants.



2.) Using a plastic lever hold back one piston while depressing the brake lever several times to push the other piston out. Be careful to only extend the piston a maximum of 5-8mm from its bore to ensure it does not pop out the calliper.



3.) Once extended from the calliper, using a syringe, carefully apply the correct oil to the outer round face of the piston. Either mineral oil or DOT oil should be used depending on your brake, so check before you apply.



4.) Push the piston back into the calliper and repeat for the other piston. Repeat this process two to three times for each side to ensure they are well lubricated.



5.) Clean the calliper inside and out using brake cleaner or isopropyl alcohol. Ensure all traces of oil are removed then refit brake pads.



EXTRA TIP => If you have four-piston brakes, use an old brake pad for a wider interface with the tyre lever to hold back the pistons.



RUBBING DISC:
1.) Remove brake pads, but keep wheel fitted to the bike. Loosen the caliper bolts a quarter of a turn and visually centre caliper over disc. Tighten calliper bolts, ensuring the calliper is still centred.



2.) Remove wheel and reset pistons into their bores using a plastic tyre lever. Refit brake pads and retaining pin or screw, followed by the wheel.



3.) Pump brake lever to extend pistons to normal working position. Spin wheel to see if disc is rubbing and assess which side of disc is rubbing. Using clean, grease-free hands, push on the disc towards the piston that is overextended. Depress brake lever at the same time to extend the opposite piston.



4.) Repeat the process until both pistons/pads move evenly.





PAD CONTAMINATION:
1.) Remove brake pads and clean calliper with brake cleaner or isopropyl alcohol and cloth.



2.) Replace the brake pads (shop here): this is the best option, as you will never get full performance back from the pads if they have been contaminated with oil.



3.) Using sandpaper, abrade disc to remove contaminant and restore braking surface to an unused state.



4.) Clean disc with brake cleaner or isopropyl alcohol and cloth. Refit wheel/disc to bike along with new brake pads and bed in.

If the rotor is too damaged/contaminated it might be worth considering renewing it. Please click here for our rotor offering.





ROTOR TRUING:
1.) Spin wheel to hear disc rubbing and locate the section of disc that is out of true.



2.) Using a very clean adjustable spanner or rotor truing tool, gently bend disc either way using trial and error until it is running straight. Start carefully as you don’t want to make it worse. Constantly reference the pad/disc gap to be sure you aren’t over or under truing.

EXTRA TIP => Be very careful with Shimano IceTec rotors as they are very soft and bend very easily due to their aluminium core.

If the rotor is too damaged/contaminated it might be worth considering renewing it. Please click here for our rotor offering.





PAD GLAZING:
1.) Glazed pads will need to be gently sanded perpendicular (at an angle of 90° to a given line, plane, or surface or to the ground) to the direction of disc movement. You only need to remove the shiny surface of the pad, try not to remove too much pad material.

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