Read our guide on how to trim and Bleed Shimano Brakes and Hoses of your mountain bike.
Tools for the job (Essential Kit):
1. Lint-free cloth/rags
2. Shimano bleed kit
3. Disc Brake cleaner
4. Mallet
5. Mole Grips
6. Marker pen
7. 8mm open spanner
8. 7mm open spanner
9. 6mm Allen key
10. 5mm Allen key
11. 4mm Allen key
12. 3mm Allen key
13. Plastic tire lever
14. Hose cutters
15. Old spike or zip ties
16. Bleed block
17. Workshop vice/clamp
1. Give your bike a thorough clean using Muc-Off cleaner. Focus on areas near and around the brake calipers and hoses, and wipe them down with a rag to dry them as much as possible. It's easier to do this with the bike in a stand, and if possible, position it close to a bench vice.
2. Many bikes come with messy hose and cable routing. This is partly because one-size-fits-all hoses are used on different bike sizes. Examine the current hose-positioning and turn your bars 90 degrees right and left to check for any snagging or odd looping twist that could damage the hose or catch stray branch mid-ride.
3. Route the hose in the smoothest and most direct way. Shorter is better, but not too short. Use an old section of hose or cable outer to help work out how short you can go. Turn the bars at least 90 degrees in each direction check you'll still be able get round corners and that there's still enough slack. Mark how much you need to trim on your current hose.
4. Remove the relevant wheel for the brake you're working on. Remove the pads and inspect them for wear. Place the pads and any retention bolts or clips on a clean rag out of the way. Lightly squeeze the brake lever until the pistons begin to move inwards. If the pistons don't slide out evenly, apply a small amount of lightweight lube to them and try again.
5. Drape a clean rag around the caliper as close to the bleed nipple as possible. Place another rag around the lever, and place either a bucket or oil pan and an old towel directly underneath the caliper on the floor. This will catch any stray drips that may occur with the overfill bleed technique. Lay out all the tools and spares you need and extra rag close to hand.
6. Slide back the rubber 8mm bolt cover to expose the bolt. Use an 8mm open-ended spanner to turn the hose connecting-bolt until the hose is disconnected. Place the nut and washer to one side. Hold the hose vertically with the end pointing up and using sharp outer-cable snips or a dedicated hose-cutting tool; trim it to the marked length. Make the cut clean square.
7. Slide on the 8mm bolt rubber cover, the hose bolt and brass olive before lightly clamping the assembly into the bench vice. If the vice has soft jaws use them or wrap an old inner tube around the vice jaws to help grip the hose and reduce crimp damage. Push in the brass-connecting insert into the end of the hose, still keeping the hose vertical.
8. If you kept the hose vertical and your braking system is fairly new, you might be able to get away without bleeding the brakes. Use a plastic tire lever to gently press the caliper pistons in, insert the model-specific bleed block, and squeeze the lever. If the lever feels firm you can skip to step 16, if it's mushy, you should bleed the system to ensure consistent stopping.
9. Loosen the brake lever with a 4mm Allen key at the lever clamp, and position it at about 45 degrees to the floor (with the bleed screw roughly parallel with the floor). Reposition the rags around the lever. Use a 2.5mm Allen key to remove the bleed screw (closest to the lever clamp) at the small O-ring on the bleed screw and insert the oil funnel into the bleed port.
10. Slot the 7mm spanner over the bleed nipple on the caliper. Attach the plastic tubing to the syringe and fill the syringe with mineral oil. Gently push the end of the plastic tube with syringe attached to the bleed nipple. Turn the spanner anti-clockwise an eight of a turn at a time, to loosen the bleed nipple and 'open' it.
11. Depress the plunger on the syringe and keep an eye on the oil funnel. You'll see the oil that's being pushed through the brake line come out into the funnel and chances are, it will have air bubbles in. Keep pushing the plunger and adding oil to the system until no more air bubbles come into the funnel. Turn the spanner clockwise to temporarily close the bleed nipple.
12. Remove the syringe from the flexible plastic tubing and drain any excess oil from the syringe back into the oil battle. Connect the oil bag onto the end of the plastic tubing. Loosen the bleed nipple by an eighth of a turn. Oil should begin to naturally flow through the system and drain into the bag. You'll also see air bubbles in the clear plastic tube.
13. While the oil continues to drain, keep an eye on the funnel and its oil level. Don't let it drop too low, keep it topped up to stop more air entering the system. When no more air is coming out of the tube, turn the spanner clockwise to gently tighten the bleed nipple back up. To rid any air that may still be trapped in the caliper, depress the brake lever into the bar.
14. With the lever depressed, rapidly (but gently) open and close the bleed nipple. It only needs to be open for about half a second at a time. Do these two or three times. Keep an eye on the tube to watch for bubbles. When you've finished, retighten the bleed nipple by turning the 7mm spanner clockwise until you reach the specified 4-6Nm torque setting.
15. Try gently operating the lever. Any remaining bubbles should appear in the oil funnel. When these stop, depress the lever fully. Insert the funnel stopper into the center of the funnel with the O-ring attachment facing downwards to plug the funnel. Wrap workshop towel around the lever ready to soak up any split oil and remove the oil funnel from the bleed screw port.
16. Replace the bleed screw with O-ring in place. Tighten until oil flows out from the bleed screw port. Finally tighten to 0.3-0.5Nm with the 2.5mm Allen key. Spray down the caliper and brake lever with isopropyl alcohol, then wipe dry. Move the brake levers back to their previous position. Go for a spin to check the brake is functioning correctly.