Your bike’s standard black, flexible, ugly hoses are prone to bulging, especially with age when the material perishes. Try this to see what we mean: wrap your hand round the existing hose, work the brake lever hard and you’ll feel the line swell in your mitts. Bulging lines are an MoT failure. The tightly wound braided steel coating on replacement lines prevents bulging.
What you’re dealing with
The black hoses don’t actually carry the brake fluid which works the pistons. It’s only a thick protective coating for a PTFE (polytetrafluoroethylene) inner pipe. Say that one after a few pints!
Don’t even think about it if…
… You hate manual labour or have a few spare quid to pay someone else to do the job. It can be dirty and nerve wracking the first time.
Stuff you’ll need
New brake fluid to the right spec. Dot4 is the norm. Instructions on the lid of the fluid reservoir will confirm this. Combination spanners (ideally 8-17mm) to undo brackets and hose banjo bolts, one metre of 5mm diameter clear, flexible tube from a car accessory shop, a disused syringe, and plenty of clean absorbent cloth. And the new brake line kit, ideally with corrosion resistant stainless steel fittings and clear plastic protective coating covering the braided line.
What can go wrong?
At worst you’ll strip the threads in the caliper and master cylinder where the old/new brake lines connect. If the new lines aren’t bled correctly you’ll have no brake pressure. Either way you’ll be in the shite financially and physically. Brake fluid is also very corrosive. Take care when handling: wash off all spills.
What skills do I need?
If you know the difference between a combination spanner and a 1/2in drive ratchet you’ll crack the job.
1. Loosen off or remove all fasteners that retain mounting brackets for the hoses. Any clamps and bolts should be kept in a safe place to be used again in case the new brake line kit doesn’t have replacements. Move the bars left or right so the master cylinder is left in a level position – you may have to undo the clamps and realign.
2. Protect surrounding paintwork and plastics by wrapping cloth around the master cylinder. Carefully remove the lid and lift clear, along with the rubber diaphragm. Wipe both parts with cloth or kitchen roll to soak up any fluid and also moisture which has formed. Remove all fluid from the master cylinder with the syringe.
3. Place the 8mm ring section of the combination spanner over one of the caliper bleed nipples (always found at uppermost of caliper). Now push the clear hosing over the nipple making sure the other end of the tube is inside a container to catch fluid. Weight the tube with an old bolt or nut to stop it flicking out and splashing fluid everywhere.
4. Apply the brake lever and keep held in. Now undo the bleed nipple a quarter of a turn. This allows brake fluid to escape from the system so there isn’t so much to drip out when removing the hoses. Close the bleed nipple and repeat the previous action until no more fluid is forced out. Do the same with the other caliper (on twin disc set-ups).
5. If you haven’t removed any mounting bolts/brackets do so now. Undo and remove the 12mm banjo bolt from one caliper. Place the end of the hose and bolt in a bag to catch fluid then tape the bag to the hose. Don’t worry about losing the washers or banjo bolt; you won’t need them. Repeat for the opposing caliper.
6. Now remove the bolt from the hose connected to the master cylinder. Make sure there is cloth to catch any drips. Wrap cloth around the loose hose end and pull the complete hose assembly clear of the bike and drop it into a plastic bag. This and any waste brake fluid needs to be disposed of at a council tip.
7. Wipe any excess fluid from threads on the calipers and master cylinder. Take the new lines and check they are the right length by holding them where they should run. If they are a direct replacement you could lay over the original lines. Check the end fittings have the same bend angles. Start off fitting the lines, working from top to the bottom.
8. Fit new sealing washers (copper crush washers) either side of the hose banjo (two per banjo bolt). On a double length bolt (two hoses) it will need three washers. Loosely tighten the bolts and align the lines, check for kinks. Tighten fully with a torque wrench if possible. Torque figures should be supplied by the brake line manufacturer.
9. Top up the master cylinder reservoir with new fluid to begin bleeding the brake lines – the same way as you removed excess fluid from the original brake lines. Pull the lever in and hold, undo the bleed nipple, close the bleed nipple, release the lever and repeat until no more air bubbles appear in the clear tubing.
10. To remove air trapped inside the lines try ‘back-bleeding’: tapping the brake lines with a spanner from the lowest point upwards. Trapped air will rise and, by gently pumping the lever, air bubbles will escape. Forceful bleeding will mean fluid jumping out the reservoir (above). Taping the lever on overnight has a similar effect.
11. Refit the master cylinder lid, seal and any clamps/brackets and again check the steering lock is not compromised. Also pull the front wheel off the floor so the forks fully extend and the lines are not stretched. Also check with the forks compressed. Look for any signs of leaks – sometimes an extra tweak of a connection is needed.
12. Wash the whole bike with warm soapy water (degrease first to play safe) as even a brake fluid smudge from a finger can be harmful. Now rinse the bike with fresh water. Refit the bleed nipple covers and take the bike for a slow, short ride – your brakes will feel a load lot better. In most cases lever travel is greatly reduced.