Repair guides › Brakes
Fix a spongy or pumping hydraulic brake
Disc brake moved by fluid instead of cable: more power, self-adjusting as pads wear. The lever piston pushes fluid that moves pistons on both sides of the caliper.
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Tools
- Ball-end hex key set (1.5–10 mm): Park Tool HXS-1.2 Professional L-Shaped Hex Set ($$)
- Shop rags + nitrile gloves: shop towels and nitrile gloves ($)
- Shimano bleed kit + mineral oil: Shimano bleed kit funnel and Shimano mineral oil ($$)
- DOT bleed kit + DOT 5.1 fluid: SRAM DOT Standard Bleed Kit ($$$)
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Steps
- Spongy feel that gets firm after a couple of pumps = air in the system.
- Quick burp: put the bike in a stand with the lever level, remove the lever bleed screw and screw in the bleed funnel with some of the correct fluid (the one printed on the lever or caliper: mineral oil or DOT, never mixed). Pull the lever slowly a few times and flick the hose; bubbles rise into the funnel. Plug the funnel and remove it.
- Refit the bleed screw. If the lever is still soft, do a full bleed.
- Lever reaches the bar (soft or firm) = do not ride. Look for fluid at the hose fittings and caliper, check pad thickness, then do a full bleed. Any leak means the part must be fixed or replaced.
- Brake drags after a long descent = fluid expanded from heat; a full bleed with the pistons pushed back fixes it.
Diagram
Cut in half, looking down from aboveDisc brake caliper (either wheel)
Signs it needs doing
- Spongy lever
- Lever pumps up
- Pads drag after a long descent
- Fluid leak