Even high-end hydraulic disc brakes can feel soft over time – like squeezing a sponge. In most cases, it’s not broken parts but trapped air inside the lines. This hands‑on guide walks you through a shop‑grade bleeding procedure using a Shimano mineral oil system (also works for TRP and most brands). Restore that firm, linear lever feel.
Flip open the rubber cover on your brake lever, then screw in a dedicated bleed funnel. Add a small amount of fresh mineral oil – about 1/3 of the funnel height – to block air entry.
Attach clear bleed tubing (2–3mm ID) to the caliper’s bleed nipple. Use an open‑end wrench to loosen the nipple by 1/4 turn. The tube end should point downward or sideways.
Connect a 50–60mL syringe filled with new brake fluid to the tubing at the caliper end. Push oil very slowly (<1 mL/sec) while watching the funnel at the lever – the fluid level will rise. Alternate push‑pull 2–3 times until the oil coming out of the tubing turns noticeably clear.
⚠️ Make sure your syringe contains only fluid, no air.
Squeeze the lever gently 2–3 times while watching the tubing for bubbles.
Tap the caliper body and hose lightly (use the plastic end of a wrench or a wooden stick) to free stuck bubbles.
Tilt the caliper: loosen the caliper mounting bolts, then angle the caliper so the bleed nipple is at the highest point. Squeeze the lever again – bubbles will naturally travel to the nipple.
When you see continuous, bubble‑free fluid coming out of the clear tube, hold the lever squeezed without releasing. Immediately tighten the bleed nipple with your wrench. Then release the lever.
If you still feel a hint of sponginess:
Remove the caliper (don’t disconnect the hose) and secure it higher than the lever reservoir – use a zip tie to hang it.
Then push fresh fluid from the lever side (using funnel or syringe) very slowly. This forces any remaining stubborn bubbles to travel upward toward the lever, where they can escape.
Remove the funnel and reinstall the reservoir screw (torque 1–1.5 N·m – do not overtighten).
Clean any spilled brake fluid with isopropyl alcohol (keep it away from pads and rotor).
Reinstall the pads and wheel.
Test: Squeeze the lever firmly 10+ times. It should feel solid with short travel. Spin the wheel – no drag.
| Symptom | Likely Cause | Fix |
|---|---|---|
| Still soft after bleeding | Air trapped at caliper top | Flip caliper upside down (nipple up), re‑bleed |
| Braking power inconsistent | Oil contamination on rotor/pads | Clean rotor with alcohol; replace pads if needed |
| Lever won’t return | Seals swollen due to wrong fluid mix | Replace all seals (never mix fluid types) |
| Leak from bleed nipple | Worn threads or wrong torque | Replace nipple – never use Teflon tape |
Crash damage to caliper or lever (micro‑cracks may be invisible)
Old fluid looks like jelly or sludge (needs ultrasonic cleaning)
You’ve tried twice and still have a spongy feel
TRP brake systems use standard bleed nipples and are very home‑mechanic friendly. Mastering bleeding gives you precise, predictable, satisfying brake feel – well worth the effort.
