Brake pad spreader
A pad spreader pushes hydraulic brake pistons back into the caliper so new pads fit over the rotor.
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A brake pad spreader, or piston press, is a flat tool that pushes a hydraulic disc brake's pistons back into the caliper. New, thicker pads need that room to fit over the rotor.
What it's used for
When you replace pads on a hydraulic brake, Park Tool says to press the pistons in with a pad spreader or with a flat, non-marring tool such as a tire lever (Park Tool pad guide). Its brake bleed guide also lists a pad spreader and piston press among the tools needed (Park Tool bleed guide).
What to look for
- A flat, non-marring surface that won't scratch the pistons (Park Tool).
- A width that suits your caliper. If you don't have one, a plastic tire lever works as a stand-in (Park Tool).
Using it safely
- Press evenly. On Shimano flat-mount hydraulic brakes, Park Tool specifically warns to apply even pressure to avoid damaging the ceramic pistons (Park Tool).
- Don't squeeze the brake lever with the wheel or pads out. If you do, the pistons come out again and must be pressed back in (Park Tool).
- Mechanical (cable) brakes have no hydraulic pistons. Park Tool says to back their pad adjusters out instead (Park Tool).
- After new pads go in, pump the lever until the pads meet the rotor, then spin the wheel to check for rubbing (Park Tool).
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