Disc brakes are now ubiquitous on Mountain Bikes but it wasn’t always the case as anyone brought up on the early MTBs of the 1990’s will confirm. Cantilever, then V-brakes offered a good amount of stopping power on normal terrain in the dry but on extreme downhills and wet, muddy rides they sucked. The first disc brakes on a production bike appeared in 1999 (Trek 8900) and were mechanical devices with brake cables. Nowadays, most decent MTBs have hydraulic disc brakes that offer oodles of power BUT can be fiddly to setup.
Once you get used to the systems though they are pretty easy to work with an actually set themselves up pretty well, as long as your discs aren’t warped and the caliper is aligned properly. Here’s our step-by-step guide to servicing your Shimano hydraulic disc brakes.
- OK, it’s going to get messy in here so make sure you have plenty of rags and have put down some protective sheeting under your bike. Using a workstand is going to make the job a whole lot easier too.
- Tools for the job include a couple of hex keys, screwdrivers and pliers – things you will find in any cyclist’s toolkit. You also need the right hydraulic fluid and either a 10mm hex key to put in place of the pads (Shimano do a special tool for this too but we found this works well enough).
- First of all remove the pads by releasing the spring clip at the back. Keep these well out of the way as you don’t want to get fluid on them as they will be contaminated and fit for the bin. Place the 10mm hex key or brake block tool in place to stop the calipers extending later on in the process.
- Now level up your brake levers. The fluid reservoir needs to be parallel to the ground so loosen the brakes a bit, adjust and re-tighten.
- Remove the reservoir lid and check the levels, with a bit of luck it won’t be dry and air won’t be in the system.
- Take the dust cover off the bleed nipple and attach the bleed hose that comes in the mineral oil pack. Turn the 7mm nut about ¼ turn to pen the valve.
- With the reservoir topped up, repeatedly pull the brake lever. You should see the old fluid start to come out of the tube and into your receptacle (we had a beaker but a plastic bag will do).
- Hopefully you won’t see any air bubble coming through, just the old liquid. Once the nice new pink stuff comes through and there aren’t any bubbles you can stop pumping and close the bleed nipple.
- Now while maintaining a full reservoir keep pumping the brake lever until it stiffens up in your hand. Now you can top-up the reservoir and put the cover back on.
- Clean up any spilt fluid from around the caliper, clean your hands and tools then re-insert the pads and the spring clip.
- Once you have fixed the wheel back on you should find the brakes are working much better and the caliper auto-adjustment should mean no rubbing. If they do try re-setting the calipers using step 7.