Bike Repair – Trim and Bleed Shimano Brake Hoses

A pair of Shimano brake hoses.

Huge arcs of brake cable protruding in front of your bar? De-clutter your cockpit by trimming your brake hoses and Restore full braking power by bleeding the brakes too.

1. Clean up

Before you start, it makes things easier if you give your bike a thorough clean. Focus on areas near and around the brake callipers and hoses. Wipe down with a rag to dry them out as much as possible. As with many other workshop tasks, it’s much easier with the bike in a stand, and if possible, positioned close to a bench vice.

2. Check your routing

Many brand new bikes have a real mess of cables in front of the bars, thanks to the long default hoses of complete brake systems. Turn your bars 90 degrees to the right and left to check for any snagging or odd looping twists that threaten to damage the hose or catch a stray branch mid-ride.

3. Measure your new routing

The aim is to create the smoothest and most direct routing. Shorter is better, but don’t go too short: use an old section of hose or cable outer to help work out how short you can go. Turn the bars right round to check there’s still slack – if there isn’t, a crash could wrench the hose right out. Mark on your current hose how much you need to trim away. Oh, and then measure it again – measure twice, cut once!

4. Disconnect the hose

Slide back the rubber cover on the lever to expose the bolt. Using an 8mm open-ended spanner, disconnect the hose (turning anti-clockwise) and put the nut and washer to one side, somewhere safe. Keep the hose vertical with the end pointing up and, using sharp outer-cable snips or a hose cutting tool, trim the hose to your pre-marked length. Aim to make the cut as clean and square as you can.

5. Refit the fittings

Slide the rubber cover, hose bolt and brass olive onto the hose (in the same order as removed) before lightly clamping it into the bench vice using the hose blocks from the bleed kit. If you don’t have any blocks, you can substitute a vice with an old inner tube wrapped around the jaws to help grip the hose and reduce damage. Push the brass connecting insert into the hose, then gently tap it in further with a rubber mallet.

6. Check pads for wear

Remove the relevant wheel, take out the pads and inspect them – if one pad is more worn than the other, or they’re worn unevenly across their surfaces, this indicates the calliper needs attention. Lightly squeeze the lever – just a fraction – and watch the pistons. If they don’t slide out evenly, apply a small amount of brake fluid around the seals and try again.

7. Need to bleed?

To check whether you need to bleed the lines, use a plastic tyre lever to gently press the pistons into the calliper, insert the (model-specific) bleed block, and squeeze the lever. If it feels firm you can skip to Step 16. If the lever is mushy, there’s air in the system that needs removing (air can be compressed, allowing the lever to move without the pads squeezing any harder).

8. Prepare to bleed

Drape a clean rag around the calliper, as close to the bleed nipple as possible, and wrap another around the lever. Put a bucket directly underneath the lever to catch the drips the overfill bleed technique creates. Have an extra rag close to hand as well.

9. Loosen the lever

Loosen the brake on the bar and angle it approximately 45 degrees to the floor, putting the bleed screw roughly parallel with the floor. Remove the bleed screw (closest to the lever clamp) with a 2.5mm Allen key, along with the small O-ring behind it.

10. Set up the syringe

Carefully insert the oil funnel into the bleed screw port on the lever. Slot the 7mm spanner over the nipple on the calliper, and attach the plastic tubing to the syringe. Fill the syringe with mineral oil. Gently push the end of the plastic tube with the syringe attached onto the bleed nipple. Turning the spanner in an anti-clockwise direction, loosen the bleed nipple by an eighth of a turn to ‘open’ it.

11. Put the oil in

Gently squeeze the syringe and keep an eye on the oil funnel. You’ll see the oil that’s being pushed through coming out, and chances are it will have air bubbles in. Keep adding oil until there are no more air bubbles. Temporarily close the nipple.

12. Drain the excess oil

Remove the syringe from the tubing and drain the excess oil back into the bottle. Connect the oil bag to the tubing and loosen the bleed nipple an eighth of a turn; oil should naturally flow through the system (thanks to gravity) and drain into the bag. You’ll also see air bubbles in the clear plastic tube.

13. Check the oil level

As the oil drains, keep an eye on the level in the funnel. Keep it topped up to prevent more air entering the system. To get rid of any air trapped in the calliper, gently squeeze the brake lever to the bar. When it looks like no more air is coming out of the tube, gently tighten the nipple back up.

14. Finish the calliper

With the lever depressed, rapidly open and close the bleed nipple (being as gentle as possible). It only needs to be open for about half a second at a time to be effective. Do this two to three times – watch the tube for bubbles. Finally, re-tighten the bleed nipple to the 4-6Nm torque setting, using a torque wrench. Release the lever.

15. Remove the funnel

Gently squeeze the lever again. Any remaining air bubbles should appear in the oil funnel. When these stop appearing, release the lever fully. Insert the stopper in the funnel (O-ring down) to plug it. Wrap a towel around the lever ready to soak up any spilt oil, and remove the funnel from the port.

16. Do the final check

Replace the bleed screw and O-ring, tightening it to 0.3-0.5Nm (some oil will squeeze out as you do it). Spray the calliper and brake lever with degreaser or isopropyl alcohol, then wipe dry. Replace the brake pads and spring in the calliper. Reposition the brake levers, tighten them, and go for a gentle spin – check they work correctly before relying on them!

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