Disc Brake Repairs & Maintenance

A disc brake is a type of brake that uses calipers to squeeze pairs of pads against a disc or "rotor" to create friction that is operated by a brake lever using a hydraulic hose that contains fluid or cable operated known as "mechanical disc brakes" and being more efficient than traditional rim brakes.
Side note: Magura make hydraulic rim brakes that are very efficient.

Disc Brake Service Centre   


Disc brakes are now found on mountain bikes at nearly every price point and they are quickly becoming the standard and moving to road bikes. 

This page is discussing hydraulic systems on mountain bikes. 

All good workshops will have bleed kits, fluids, cleaning fluids, hose-cutting tools, hose pin fitting tools, rotor truing fork, piston press tool, frame-facing tools and the know how.

Mobile workshop - Disc brake service center

Making it easy "We come to you, saving you time"

Disc brakes are great when set up correctly and maintained:
  • Keep disc brakes spinning and free of noise
  • Keep disc and pads clean from oil especially be very careful when using aerosol lubes and polishes on your bike, as pads and discs will become contaminated making parts unserviceable. 
  • When cleaning rotors use a paper towel, as it's clean and free of lint.
  • Fine to medium emery cloth or wet & dry paper is useful to clean brake pad surfaces & rotors, removing glazing and other contaminants. Then test brakes before using on the road. If this does not improve your braking or brakes continue to squeal "a vibration" first replace disc pads, before changing rotors. Presuming rotors are free from groves, wear or damage. Lay the wet & dry paper on a flat surface, and with a circular motion lightly rub the brake pad on the wet & dry paper for a few seconds at a time or until the pad surface is flat and uniform.
  • Rotor inspection and cleaning: The next task is to recondition the rotors by removing any glaze that may have accumulated on them. Fold medium wet & dry paper around a straight block to create a flat sanding surface. Rub the wet & dry paper tangentially on both sides of the rotors braking surfaces. For best results remove the rotor and lay on a flat surface, use the sanding block to sand the surface of the rotor then turn over and repeat. 
Recommended servicing intervals
Regular maintenance and periodical checks will keep your bicycle working better, last longer and increase the pleasure of your cycling. 

Cycle Tech recommends periodic inspections of your disc brake pads, for wear and leaks from the hydraulic system. Brake pads can wear unevenly or just one pad can wear down to metal, reducing your braking efficient and damaging the rota making it an expensive repair. Also routing inspection, check hoses for kinks and any rubbing that can wear the hose. 

Inspecting brake pads for wear:
  • Put the bike in work-stand and remover both wheels better access to the pads
  • Use a brush to clean any mud or a rag to clean dirt from the caliper
  • If you cant see pads for signs of wear clearly with an inspection torch, then remove pads
  • Inspect their thickness and condition. Look for a minimum thickness of 1.5 mm and check the condition of the pad, making sure they are not marked or contaminated with oil.
There are various methods of removing your brake pads. Some brake pads are removed by unscrewing a pin out or removing a split pin from the caliper or simply just clipped into the piston.
DO NOT UNSCREW THE BOLTS HOLDING THE TWO HALVESs OF THE CALIPER TOGETHER, this will cause a fluid leak! If you are unsure how to remove the pads, check your brake manufacturer’s owners manual or website for details.

Note: When replacing disc pads - Clean piston seals and rotor plus inspect rotor for damage. Align pads and test.

Brake bleed service: Once a year or as needed 

Hydraulic brakes are designed to use one of two main types of brake fluid - DOT fluid or Mineral Oil

Note: You can mix DOT 3, 4 & 5.1 brake fluids, it may drop the overhaul boiling point they are all Glycol based fluids. DO NOT USE OR MIX WITH DOT 5.0 this is a silicone based brake fluid. Or mix mineral oils with DOT fluid.
Mixing mineral oil - only after manufacturer's warranty has run out

Glycol based fluids are hygroscopic which means they absorb water/moisture from the environment at normal atmospheric pressures at a rate of 2-3% per year. This process is exasperated in more humid conditions and climates. Water mixed with DOT fluid has an adverse effect on the brake fluid by reducing it's boiling temperature and therefore reducing it's performance.

Before bleeding hydraulic brakes:
  • Identify the braking system as mineral oil or DOT brake fluid.
  • Remove wheels and brake pads.
  • Clean caliper pistons and bleed nipple ports with brake cleaner spray.
  • Push pistons back "to preset" and fit retaining block. (Note if pistons will not return using a little force, you will need to release pressure by loosening the bleed screw at the leaver)
  • Now bleed brakes as manufacturers recommendations using the correct tools 

Cycle Tech Disc Brake Bleeding
 Bleeding disc brakes

See our how to videos below for Avid and shortning a Shimano hose

Retaining block
Retaining block - Also used for transporting when front wheel is removed to stop brake pistons moving in and making it difficult to refit front wheel. 

A brake piston press pushes the pistons back into the caliper bores. By sliding into a hydraulic disc brake caliper to preset the piston when replacing pads, aligning pads, and performing other service procedures. Making hydraulic disc brake maintenance and repair faster and easier.
Side Note: You can also use a plastic tyre lever on older systems, for newer hydraulic systems can be too easy to damage the pitons from the material (composite or ceramic) they are now made from. So we have found the best tool is a cone tool with a plastic handle. Used flat across the pistons face pressing and NOT using as a lever. 

Inspecting worn disc brake pads
These pads are clearly worn with uneven piston alignment


Worn disc pad
Worn disc brake pad. Note: rotor has worn return spring in to the pad!

Rotors

Disc Brake Rotor
Disc brake rotor replacment
Use loctite on threads or use new bolts that already has loctite

When applying torque to the bolts, it should be done evenly and not in a circular pattern.

Re-aligning rota
 Re-aligning rota

To help with the annoying scrape of a bent (or warped) rotor. 

Adjust rotor alignment using a gauge such as a 5 mm hex key, while spinning the wheel to indicate where the rotor is bent. Then check pads for wear, re-center pistons, and caliper to the rotor. 

Rotor inspection and cleaning

The next task is to recondition the rotors by removing any glaze that may have accumulated on them.

One of the most advanced designs is the "floating rotor", made of two different materials connected together. These are exceptional brake rotors, as they are very rigid and won't bend sideways easily. Overheating is much less of a problem and they don't bend that much because of the material expansion. Usually, the spider in the middle is made of aluminum alloy, but you can get rotors with a carbon core.

Hose fittings

Fitting of Brass Barbed Hose Pin "insert" 
Using Shimano's plastic clamp held in a vice and gently tapping with a hammer to insert the pin

Replacing hoseing first measure the lengths of the old brake hoses to determine the proper cable routing and new lengths.

Tektro Auriga Comp compression ferrule
Tektro Auriga Comp compression ferrule (Olive) Correct fitting.
Cover, connecting bolt, olive "the correct way around2 and insert

Lubricate parts with mineral oil (Or fluid depends on system) before inserting the hose into brake lever or caliper. This will ensure good fitting of o-ring on the brass pin and stop hose twisting on tightening.
Compression ferrules (Olives) are fairly easy to fit and make a secure joint. They're also fairly straightforward to remove later. 
Side Note: Do the job correctly - The olive is a compression fitting and should not be reused, as could result in causing a leak and olives are cheap to buy. 

Brake hose cutter
Magura hose cutter

When cutting brake hose, use proper hose cutters that leave's a nice flush finish to the hose ends. 

How To Video - Shortening Shimano disc hose Video

Video - How to shorten a brake hose without bleeding the brake afterward's, when fitting a new Shimano brake system. 

Fitting new Shimano disc brake kit with over length hose, if you do it correctly there is no fluid spillage and the brake won't need bleeding afterward's. Always keep the hose end up so that no fluid will be not be lost from the hose. You can use the fluid from the off cut and top up if any fluid was lost when cutting hose to length.
Put a drop of fluid on the end of the hose, connecting bolt, olive and insert before fitting, this is to stop the hose turning when tightening.  
When cutting brake hose, use proper hose cutters that leave's a nice flush finish to the hose ends.

Tools:
  • 8 mm spanner
  • Hose Cutter
  • Needle-pin press or Shimano's plastic clamp with the kit
  • 4 & 5 mm Hex keys


How To Video - Avid Hydraulic Disc Brack Stuck

Video - How to free off Avid hydraulic brakes. 

Symptom: Wheel rubbing on rotor "brake binding" or wheel not turning and brake lever is also hard to pull.
Fault: Brake system overfilled. By opening the bleed screw by two turns and pushing pistons back in the caliper. With the bleed screw, open releases pressure in the system and a small amount of fluid is released, when pistons are pushed back

Tools:
  • Torx T10
  • Disc brake piston press
  • 4 & 5 mm Hex keys


Video - Hydraulic Disc Brake Inspection

Video - Disc brake inspection
Regular maintenance and periodical checks will keep your bicycle working better, last longer and increase the pleasure of your cycling. 

Hope brake olive fitting

Re fitting Hose through swinging arm

Braided Hose
When reusing an olive, use a screwdriver to open up to fit over the hose and the reclose 

Put a drop of brake fluid on the threads and olive fitting to banjo, to stop hose turning when tightening 


Upgrading your disc brakes. Shimano sells a very good system that comes complete with a leaver, hose, and caliper (Including pads) SLR's are a great begin.  
Adding a bidder rotor to the one you have will give you much better braking. You will need to change the mounting bracket to cater the bigger rotor. 
If you are looking for something better then XTR's, or the Magura and Hope Tech twin pot brakes are a very option to give you the ultimate in braking.  

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