The pad position will need adjusting after changing a brake cable, after fitting new pads or as the pads become worn. Ideally, the pad position should be set so that you can lock up the wheel by pulling the brake lever halfway to the handle bar. This gives you enough lever movement for precise speed control, without the risk of trapping fingers between lever and bar during emergency stops.
Mechanical disc brakes can be fiddly to adjust.clearance between pads and rim must be small, withoutallowing the pads to rub on the rotor. A common source of The confusion is that only the outer brake pad gets moved by the action of the cable, pushing the rotor against a stationary inner pad. This means that the two pads have to be adjusted in different ways.
You will really benefit from a workstand for this task. If that’s not possible, press-gang a mate into lifting the wheel off the ground at opportune moments. Before you start adjusting, spin the wheel, look into the calliper slot and check how much clearance there is between rotor and pads. If the brake binds as you ride, one or both pads are rubbing on the rotor and need to be moved away. If you’re finding that you can pull the rotor all the way back before the wheel locks, one or both of the pads needs to be moved towards the rotor.
“The clearance between pads and rim must be small, without allowing the pads to rub”
The calliper slot is quite narrow, and it can be tricky to see what’s going on. Clean the calliper before you start trying to make adjustments. Then hold something white on the far side of the slot to make it easier to see the gap. Spin the wheel while watching the slot. Unless they’re brand new, rotors will often have a slight wobble. Make sure you adjust for an estimated central position.
Adjusting pad position
Before you start adjusting the pad position, ensure that the rotors are not dragging on the side of the rotor slot — this will damage the rotors and slow you down. Adjust the calliper position (see the calliper fitting), so that the rotor runs centrally before you adjust the pad position. Check that the wheel is properly and securely located in the dropout too — the rotor position will be affected if the wheel’s not straight in the frame or forks.
It’s worth keeping a spare set of brake pads. There is no standard size and shape (unlike V-brake blocks), so it can be tricky to find the right one. Spares are light and easy to carry for emergency replacement, but it’s far easier to adjust pads at home than out in the open because the job involves too many small fiddly bits aching to start a life of freedom in the long grass beside your favourite trail.
Tools to fit new callipers
- Allen keys — 5mm or 6mm, to fit heads of fixing bolts
- For IS mount callipers — a selection of shims. Useful sizes are 1mm, 0.5mm and 0.25mm
Tools to change brake pads, and adjust pad position
- Depending on model, pliers to extract and refit split pins
- Fresh pads of correct make and model
- Allen keys for stationary pad adjustment bolt — usually 3mm, 5mm, or Torx TX25
Source : BIKE MAINTENANCE TIPS, TRICKS & TECHNIQUES