Repair guides › Brakes
Adjust a U-brake
Compact rim brake mounted on the seat stays (older frames: chainstays), tucked under the frame, so nothing sticks out to catch on grinds. Two arms pivot on brake bosses. A straddle cable (or a 990-style link) pulls both arms together, squeezing pads onto the rim. Spring tension screws balance the arms. Pads are flat and often wider than V-brake pads.
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Tools
- Ball-end hex key set (1.5–10 mm): Park Tool HXS-1.2 Professional L-Shaped Hex Set ($$)
- JIS #2 screwdriver: Vessel Megadora JIS screwdriver #2 ($)
- 1/4" click torque wrench (about 2–17 Nm) + bits: Pro Bike Tool 1/4 inch drive click torque wrench set (2.2–16.9 Nm) ($$)
- BMX axle wrench 15/17/19 mm: BMX axle wrench 15 17 19 mm ($)
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Steps
- Loosen each pad nut. Squeeze the arms so the pad sits flat on the rim's braking surface, not touching the tire, with the front of the pad slightly closer (toe-in).
- Tighten the pad nuts.
- Set the straddle cable so the arms pull evenly; tighten the main cable so pads sit 2–3 mm from the rim.
- Balance the arms with the spring tension screws: if one pad drags, add spring tension on that side.
- Squeeze hard 10 times, recheck the gap and balance.
- Clean the rim with isopropyl alcohol if peg wax or dirt got on it.
Torque
| Fastener | Torque |
|---|---|
| Pad nuts | 6–8 Nm |
| Arm pivot bolts | 5–7 Nm |
Diagram
Side view, chain side toward youRear brake + Handlebar
Signs it needs doing
- One pad rubs the rim (spring tension out of balance)
- Squealing (pads glazed or no toe-in)
- Lever pulls to the bar (cable stretched or pads worn)
- Weak braking (rim dirty or wax from grinds)