Badly set up brakes can be a real drag (groan). They can slow you down when you don't want them to, or fail to stop you properly when you do.
Common problems include the calliper being poorly aligned with the
rotor, one piston moving more than the other, bent rotors and contaminated
pads. These can all cause your brakes to squeal like a banshee, while doing
very little to actually slow you down. Poor alignment or uneven pad movement
can cause your pads to contact the rotor at an angle, which creates a squealing
noise, as well as a lack of power and a spongy feeling at the lever.
The why
Most modern brakes perform brilliantly if set up correctly. The
performance differences between competing systems are slight compared to the
contrast between properly and improperly setup brakes. Follow this guide to get
your stoppers performing at their best: boosting their power and lever feel,
while minimising drag and noise.
The how
This is a troubleshooting guide only; if you're unsure of any of the
steps, ask your local bike shop.
Whatever the issue with your brake, it's worth making sure the calliper
is perfectly aligned with the rotor. With the wheel properly installed, and in
a well-lit location, look through the slot in the calliper to check that the
gap between the pads and the rotor is even on each side, and along the length
of the pads. If it isn't, loosen both calliper bolts (anti-clockwise) and
retighten them to moderate torque, just enough to hold the calliper in place.
Identify which end of the calliper is most off-centre, loosen the corresponding
bolt and move the calliper towards the centre, before retightening the bolt to
a moderate torque. Repeat this process at both ends until the brake pads are
evenly spaced from the calliper.
When you come to retighten the calliper bolts for the final time, it's
important to turn them incrementally. Tighten one slightly, then the other.
Alternate until both bolts are tightened to around 5Nm. If you tighten one
completely without touching the other, the torque you apply may twist the whole
calliper. Once tightened, check the rotor is still central in the pads. Repeat
if necessary.
Next, spin the wheel and listen for the disc rubbing on the pads. If
the disc rubs most of the time, repeat the calliper alignment step. If it rubs
for a small section of the rotor, it's time to true the disc. First, identify
which part of the rotor is rubbing by listening for the noise as it spins. Stop
the wheel at the point when the rotor is rubbing on the calliper, then look
through the slot to see which side of the rotor is bent. Noting the position of
the bent section, turn the wheel until this section is out of the calliper.
Bend this section in the opposite direction using a clean adjustable spanner, a
specialist truing tool or your hands. Spin the wheel and listen again for
rubbing. Repeat this step until there's no rub.
Squeeze the lever while looking through the calliper slot. Check to see
if the pads move together evenly, and contact the rotor simultaneously. If they
don't, this can cause squealing and a spongy lever feel. Remedying this is
beyond our quick guide, but your local bike shop should be able to help. The
process involves pushing the faster-moving piston back in and squeezing the lever
to force the other one out.
If the lever still feels spongy, the brake needs a bleed. If the brake
is still excessively noisy and low on power, it is probably contaminated. In
this case, replace the pads and give the rotor a thorough clean with a disc brake
cleaning spray and clean rag. Bed-in the new pads in dry conditions before you
expose them to mud and water. You need to ensure that your brakes have plenty
of power before you start hitting the trails.
BASIC TOOLS
- Adjustable spanner
- Brake cleaning spray
- Clean rag
- Brake bleed kit