SA, Golden Grove, Wednesday 19th September 2012
How to bleed your brakes - a MotoBuzz guide - by Kym Liebig
While I do more than my fair share of waffling, now and then I try to be at least a little bit useful. My wife will tell you that I serve a similar purpose around the house; mostly waffley with occasional bouts of usefulness. So here goes.
One thing that often comes up in conversation when talking with fellow bikers is bleeding brakes. Now, that's not me putting an endearing Brit spin on 'bloody brakes', it is, of course, accurately referring to the bleeding of fresh fluid through your brake system, expelling bubbles as you go. The subject seems often to be shrouded in mystery, and seen as something of a challenge, but with a few simple tips, it's quite straightforward. Running a track bike as I do, I find myself undertaking this job so often nowadays that I probably have faint permanent traces of Dot 4 fluid in my blood.
Why bleed brakes?
Really? Okay, I'll humour you. Your brake fluid is subjected to all sorts of abuse. It cops intense pressure as part of normal use, and is subjected to extreme heat (transferred from the discs, through the pads, to the pistons, to the fluid) often. Heated fluid slowly degrades the brake lines and picks up contaminants from them. Brake fluid is also hygroscopic - it draws in water vapour from the air. Pure brake fluid has a very high temperature tolerance, but old brake fluid that has picked up plenty of water can boil when subjected to high temperatures at the caliper. Boiling water creates steam, steam creates bubbles…and bubbles make your brakes go soft at best, and disappear at worst. So it's a good idea to keep fresh fluid in, and thus water and air bubbles out.
Can anyone bleed brakes?
It's really not that hard. If you can tackle basics like changing your oil and adjusting your chain, you should be able to handle brake bleeding without any drama.
A word of warning…
Brake fluid is awful stuff. It's toxic, sure, but it's also corrosive. Spill it on your bike's paintwork and plating, and if you leave it for any length of time, it'll eat right through it. If this is your first try, you're bound to spill a bit here and there - even if it's just a few drops - so keep an eye out, keep some clean rags handy, and clean up right away.
What you'll need;
· Ring or box spanners to fit the bleed nipples on your master cylinder (not all master cylinders have bleed nipples) and brake calipers. Often these are 8mm, but this can vary, so check and get the right fit.
· The correct sized screwdriver to remove your fluid reservoir cap screws, if indeed yours is held on with screws. Some are just screw tops.
· Plastic or rubber tubing that will fit your bleed nipples. Often battery breather tubing is a good fit for this, but check your nipples (oo-err…
and work something out.
· A screw top plastic soft drink (or similar) bottle.
· A fresh bottle of brake fluid of the correct Dot specification. You'll find advice on the right Dot for your bike either printed on your brake fluid reservoir cap, or in your owner's manual. Or even on the internet…
· Plenty of clean rags.
· An attractive helper, if possible. Even an unattractive one will help at a pinch. Mind you, if you're reasonably coordinated you'll be able to do the job solo.
Let it bleed. (sorry…
1. We'll tackle your front brakes first. Take a look at your front brake master cylinder - yep, that's the 'pump' that's operated by your front brake lever. Does it have a bleed nipple? Many 'conventional' master cylinders don't, but many modern radial types do. If you find a bleed nipple, the job starts here.
2. Firstly, wrap your brake reservoir in rags (to catch any spillage) and carefully remove the cap. Screw top types are generally no problem, but if you have the type that is held on by flush screws, be absolutely certain your screwdriver is a perfect fit, as these screws are often made of cheese, and the heads are easy to strip. The lid will contain a rubber flange. Carefully remove the lid and the flange and set them aside on a clean rag.
One example of a front brake fluid reservoir, cap off. Oh good grief look at that! Low level, old, dark liquid. Disgraceful.
3. With the bleed nipple located, fit the spanner over the nipple and make sure that there is enough room for a single 'open/close' sweep of the spanner amongst all the cables, throttle grips and gubbins. Using a ring spanner here means that the spanner end can stay on the nipple as you bleed it without falling off, and also reduces the chance of spanner slip and nipple damage.
4. With the spanner on the bleed nipple, fit the rubber tube onto the nipple, place the other end into your plastic bottle, and we're ready to start bleeding.
5. Make sure that your reservoir is topped up with fresh fluid, and be careful, because of course a bump of the handlebars will spill fluid. That attractive helper is handy here, too. Now…undo the bleed nipple perhaps one eighth of a turn while at the same time gently squeezing the brake lever. When the brake lever comes back almost to the grip, tighten the nipple again before releasing the lever. Fluid - possibly grubby and very likely bubbly - will start to flow through your tube and into your bottle. The target is no grubbiness, and no bubbles. Topping up your reservoir as you go, repeat this 'undo and squeeze, tighten and release' sequence until you're giggling with the sheer joy of it all. Or at least until there are no more air bubbles. Tighten the bleed nipple, carefully remove your bleed hose and wipe everything down.
Bleeding a front brake master cylinder. It's all about getting that 'undo and squeeze, tighten and release' sequence going.
6. With the master cylinder bled, move on to the brake caliper nearest the master cylinder - 'closest downstream', if you like. Of course if your master cylinder has no bleed nipple, your bleeding starts here. Again, attach your spanner to the nipple first, then your bleed hose and bottle. If you have arms like an orang-utan, you'll be able to do the 'undo and squeeze, tighten and release' sequence solo. If not, get that helper on the job. Now that you're down by the wheel, don't forget to keep an eye on your fluid level at the reservoir, and keep topping it up as necessary. Remember, if it runs too low, it'll gulp air…and you'll have to start again. The aim as always is clean, clear fluid with no air bubbles.
Getting busy down at the brake caliper end of things…
7. Got twin discs? It's time for the final one. Same sequence as always, remembering to watch for air bubbles and keep that reservoir topped up.
…and giving the left nipple equal attention. Always a good idea.
8. All good? Then make sure all your bleed nipples are snug, clean up, wipe everything down and replace the cap on your fluid reservoir after topping it up to the correct level. Chances are by now your lever feels firmer and better, and your reservoir looks like it has been filled with fine, pale brandy rather than black sludge. (Of course if your reservoir IS filled with fine, pale brandy, you may have become distracted at some stage.)
Tips and tricks
· When squeezing your levers, don't squeeze fast, and don't squeeze all the way back to the grip. Squeeze too fast and you might cause a fountain to pop out of your reservoir, spilling fluid everywhere. Squeeze too far and you could damage your master cylinder piston and seals.
· I go one step further with my hose/bottle rig, drilling a hole the diameter of the bleed hose in the plastic bottle cap, along with a tiny 'breather' hole, then threading the hose into the bottle cap and screwing it back on. Less spills that way.
· I always 'rehearse' the loosening of all bleed nipples, backing them off just a tad before I get started. The last thing you need with an open topped reservoir is to be heaving on a frozen bleed nipple half way through the job, upsetting the bike and spilling fluid everywhere.
· Still suspect you have bubbles trapped in there? Take a screwdriver and gently tap it along the full length of your brake lines. This little bit of persuasion often gets stubborn bubbles moving.
· Nitrile workshop gloves - cheap from eBay and more pleasant than hands covered in brake fluid.
And there you have it. A simple, straightforward job that improves your brakes and makes you feel good about yet another aspect of bike maintenance. Why pay a mechanic for something so simple, or wait until service time to have it done, when you can keep your brakes at their best so easily? Once you've had some practise you'll find that you're able to do it quickly and efficiently, too.
Want to see more of these 'how-to' guides on MotoBuzz? Let us know what you'd like to see. And join in the buzz on our
Facebook page and tell us how you feel about maintenance jobs like these. Something you do all the time, something you'd have a go at to save a buck, or do you think brake maintenance is best left to the professionals? Have your say now!
Yours in the shed
Kym