Category Archives: Maintenance

Bleeding hydraulic brakes

So you’ve got some fine-ass hydraulic disc brakes on your mountain bike.  They’re great.  No cable stretch!  No messing around with tension!  Excellent!  They feel direct and firm and reliable.  And then, at some point, they stop feeling like that.  You can squeeze the lever right in after the pads have contacted the rotor.  Or, as happened with mine, once the brakes heat up from use they lock on to the rotor and you have to sit at the side of the trail and wait for them to cool down before carrying on.  There’s air in your tubes.  Your brakes need bleeding.  Simply, bleeding is the process of getting air bubbles out of a hydraulic system.

The process for bleeding brakes depends on the equipment you have and on your system.  Essentially you add new fluid to one end of the system and remove it from the other, hopefully flushing out any air bubbles in the process.  There are kits available which include a huge number of parts.  After a little research I decided on the basic equipment and procedure below, but I suggest looking into it a bit yourself.

Stuff you’ll need:

Well this will vary considerably depending on the brake system you have, and on precisely what manner of bleeding you feel like doing.  Here’s what I used.
Brake fluid.  Use what the manufacturer of your brake system recommends.  Shimano brakes use mineral oil, others use more traditional brake fluid.  You need to use the right one as the wrong one will degrade the seals and cause corrosion in your system.

Syringes.  Two of them.  I had one that I bought in a ‘bleed kit’ and one that I bought from a farming wholesalers.

Tubing.  It should fit tightly over the end of one syringe and over the bleed nipple on your brake calipers.

A spacer of some sort.  I used a stack of plectrums.  Other people have used credit cards, an appropriately sized hex key or a specific Shimano spacer block.

Torx drivers.  The top of my master piston is secured by two T10 Torx screws, and the bleed cover by a T8 one.

Hex keys.  You don’t have hex keys?  How on earth are you maintaining your bike?


Step one: Prepare the bike.  Set the brake lever so that the reservoir on the top is horizontal.  You should also wind the reach of the lever out to its fullest extent, although I forgot to do this and it didn’t seem to affect things too much.  At the other end, remove the brake caliper from the bike.  This takes it nicely away from the rotor so you’re less likely to contaminate it with oil.  Remove the brake pads (see the brake pads post for how).  Push the pistons back into place and insert a spacer where the pads and rotor would normally be.

Useful things...

Useful things…

Step two: Open the top reservoir.  Take out the two screws holding the top down and the bleed cover and lift off the cover, and the rubber diaphragm beneath.

These two...

These two…

... and the diaphragm...

… and the diaphragm…

... leaving the oil exposed.

… leaving the oil exposed.

Step three: Attach the tubing to the syringe and draw up a syringe full of oil.  Uncover the bleed nipple on the brake caliper and attach the end of the tubing to it.  Ensure it’s a good fit, it’s annoying to have it slip off.  Once it’s secure, undo the screw to open the bleed nipple by about a quarter turn.  Sometimes this means undoing the bleed nipple itself (and so you’ll need to make sure you have a spanner on the nipple before you attach the tube), but in the case of my brakes it’s a hex bolt at right angles to the nipple itself.

Bleed screw arrowed, and the tube attached to the nipple itself.

Bleed screw arrowed (in front of the connector for the hydraulic line), and the tube attached to the nipple itself.

Step four: Clear the caliper.  Push a few cc’s of oil into the caliper with the syringe, give it a couple of taps and then draw the plunger back a bit on the syringe.  This should clear any air bubbles caught up in the caliper.  It certainly did with mine.

Step five: Bleed bleed bleed.  Now comes the bleeding itself.  Slowly press the syringe attached to the caliper and inject oil into the system.  At the same time, dip the other syringe into the reservoir on the handlebars and draw the plunger back, drawing old oil and air bubbles out of the system as you refresh it from the bottom.  Carry on doing this until the colour makes it clear that it’s new oil going into the syringe and there aren’t any bubbles coming out.

Step six: Close the bleed screw on the caliper (gently, overtightening can damage the seals), and pump the brake lever a couple of times.  It should feel firm even with the reservoir open.  Then open the bleed screw again and inject enough to bring the level right up to the top of the reservoir.

Step seven: Reseal.  Close the bleed screw again and detach your tubing.  Put the diaphragm and the cover back on to the reservoir at the top – it should overflow a little bit.  Screw it down nicely.

Step eight: Clean everything up.  All the oil that leaks out or gets everywhere needs to be sorted out at this point.  Particularly at the caliper end.  Use degreaser or isopropyl alcohol to clean stuff down.  The idea is that it shouldn’t have any chance to contaminate the brake pads once they’re back in.  Speaking of which…

Step nine: Put the brake pads back in.  See the post on changing brake pads.  It’s basically the reverse of taking them out.  Reattach the caliper to the frame, making sure the pads are properly set up round the rotor.  Put the brake lever back to the position you want it in.  Experiment with the brakes to make sure they still work.


A final note.  I ended up bleeding my brakes twice in fairly quick succession.  Anyone who read the previous version of this final note will recall that the first time it didn’t entirely fix the issue.  The second time it did.  Inevitably, the first time you attempt something like this you’ll make mistakes.  I think I didn’t have the bike upright enough the first time, and the tube coming loose from the nipple didn’t help.  It’s also possible that the seals on the brakes are a bit iffy, which means I should replace my brakes, but they seem to be working fine for the time being.

As always, if the first time seems to only be a partial success, try it again.


Hahaha, nipple.


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Disc brake pads

Like all mountain bike brakes, disc brakes rely on friction pads that gradually wear and need replacing.  At first glance it seems more awkward than the more obvious pads for V or cantilever brakes, but the truth is that it’s a simple procedure.  As always, the details I give here are for my brakes.  There are variations in exactly how it works, but the principles in each step are identical – it may just be a case of looking at your own brakes to work out what needs doing.

Stuff you’ll need:
Replacement brake pads.  These come in a number of shapes and sizes, although from what I’ve gathered, if it looks right it probably is.  Don’t try sticking circular pads into a rectangular slot, but if it looks the same then it’s probably the right one.  Take your old pads in and match them up would be my advice.  After that there’s a choice of sintered (metal) or organic pads.  Supposedly they act differently, but my experimentation hasn’t yielded an appreciable difference.
Pliers.  Ones with a thin nose.
Hex keys.  You don’t have hex keys?  How on earth are you maintaining your bike?

Step one: Get access to the pads.  You can’t change the pads with the rotor between them, so you need to either take the wheel off the bike (which means you don’t have to align the brakes afterwards as nothing has really changed), or take the caliper off the frame (which means you can wave it about and get at the pads easier).

Step two: Free the pads.  There will be some device that locks through the pads and prevents them from just dropping out.  In my case there’s a split pin that threads through a hole in the caliper, through the brake pads and leaf spring, and through another hole in the caliper.  Straighten the ends of the split pin and draw it out from the other end.  Other designs have a screw here that’s locked with a split pin, or something else.  Work out how it comes out and have it out.

Straighten and remove the split pin...

Straighten and remove the split pin…

Step three: Remove the pads.  On my brakes they’re removed from the other side of the caliper from the split pin.  Squeeze them together slightly and draw them out from the caliper.  Keep hold of them – you’ll have three things in your hands: two brake pads and a leaf spring between them.

Remove the pads...

Remove the pads…

Step four: Push the pistons back into place.  The pistons automatically adjust for wear in the pads, so you’ll never be able to jam the rotor back between your new pads if you skip this step.  Stick something between the pistons in the gap where the pads were, and push them back until they’re pretty well flush with the caliper itself.  Push on the edges of the pistons not the middle – there’s nothing much there to push on and you could easily rupture the diaphragm at the other end of the piston.

Push the pistons back...

Push the pistons back…

Step five: Insert new pads.  Open your new pad pack and make a sandwich of the two pads facing inwards with the leaf spring seated between.  It should be obvious how it goes, since it’s the same shape as the pads, and should fit nicely around the friction surface of the pads.  Pinch them together from the fat end and insert them into the caliper the same way the old ones came out.  They should seat nice and firmly in the caliper.

Step six: Lock them into place.  Reinsert the split pin you took out earlier, making sure it goes through the two holes in the caliper, both brake pads and the leaf spring as well, and then bend the end of one of its arms to hold it in place.

Step seven: Put stuff back where you found it.  Put the wheel back on, ensuring that the rotor sits neatly between the pads, or reattach the caliper and set it up carefully.  Job done!

Step eight: If your new pads are organic ones, you need to bed them in properly.  It’s recommended that you do twenty or so sharp stops at speed (read the sections on braking to make sure this doesn’t mean twenty graceful dives over the handlebars).  Otherwise you could end up peeling the braking compound away from the back plate.

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Gear Cables

At present, I have only replaced my front gear cables, so this post will be limited to those.  More on the rear once I’ve replaced them as well – which may not be too long as the outer to the rear cable is fraying as well.  Again, this is the procedure with my bike, with external routing, trigger shifters and standard derailleurs.  Others may be different.  I also made it far more difficult for myself than it needed to be, so this is the version missing out my mistakes.  It’s also worth noting that it’s pretty much an identical process to replacing a guitar string, for those who’ve done that…

Stuff you’ll need:
Replacement cables.  I’m not an expert on these, but judging by the fact that I bought fairly generic MTB gear cables and they fit without any problems it seems like there’s some pretty standard fittings.  Having said that, I have Shimano shifters and bought Shimano cables, so maybe that has something to do with it.
Screwdriver.  A decent sized cross-head screwdriver with a reasonably lengthy shaft on it.
Pliers.  Possibly not totally necessary, but makes the whole thing easier.
Cable cutters.  I’m not saying it’s not possible to change cables with standard wire cutters or even a kitchen knife, but I will say it’s a great deal better with cable cutters.  Cutting cables with other things frays the end of the cables and deforms their shape, giving them weak points.  It’s also going to be a minor nightmare getting through them, whereas the cutters will manage them with ease.
Hex keys.  You don’t have hex keys?  How on earth are you maintaining your bike?

Step one: Remove the cable end on the old cable.  You’ll notice it’s been crimped to the cable, so grab it with pliers or the crimpy bit of the cutters, and squeeze it back until its round.  Then give it a sharp tug away from the cable and it should come off easily enough.  Alternatively, cut the cable just before it.

Step two: Release the cable from the derailleur.  Release the hex bolt that holds the cable grip until the cable comes free.  I think it’s a 5mm hex bolt, but experimentation should find the one you need.  Give it a couple more turns, as it’ll be a lot easier to get the new cable in if there’s a little space to work with.

Step three: Un-route the old cable.  Pull the cable outer out of its braze-ons around the seatpost and pull the outer off the inner cable.  Make sure you keep the outer.  Do the same at the handlebar end, and you’ll find you have a length of bare cable trailing out of the shifter.

Step four: Free the cable from the shifter.  Looking at the shifter from the end of the handlebars, you should be able to see a plastic cross-head bolt nestled in behind the shift levers.  You might need to loosen off the brakes to get decent access to it.  Undo the plastic bolt (it’s very short and should come out on the end of the screwdriver), and push the cable through from the other side.  The ball end of the cable should appear, and you can grab it and pull the whole cable through the shifter.  If you’re me, this step also involves examining the shifter and unscrewing every screw you can find, and ending up with a pile of irrelevant bits of shifter and no closer to working out how the cable comes out.  Don’t bother with that, experience tells me you’ll feel like a fool.

Step five: Cut the new cable to length.  Lay the ball ends of the old and new cables together and cut the new cable to the length of the old cable, allowing for the bit that you might have cut off to remove the cable end.  Do the same with the outers, cutting two new outer sections the same length as the old ones.

Step six: Prepare your outers.  Put an end piece (provided with the cables) on each end of each section of outer.  This will stop the outer from fraying and splitting from the end.

Step seven: Restring your bike.  Thread the cable through the shifter in the same way you took the old one out (it might need a little gentle poking to go through) and pull it all the way through.  A couple of tugs on it should ensure it’s seated nicely in the shifter.  Thread it through the longer section of outer (if your cable cutters have produced a nice clean cut it should go through quite easily), and then seat the outer in the braze-ons that it came out of.  Do the same with the outer that sits under the saddle.

Step eight: Reattach to the gears.  Click the shifter into the lowest gear.  Put the end of the cable securely in the cable grip.  Grab the end of the cable with pliers and pull it nice and taut, and tighten the cable grip nut while keeping the tension on it.

Step nine: Finish the job.  Stick a metal cable end onto the end of the cable and crimp it on tight with the crimpy bit of the cutters.  Make sure the end of the cable doesn’t catch on the cranks or anything else.  Adjust your gears so that they work nice and smoothly again.  Chances are the limits on the derailleur won’t have changed significantly, so your adjustment will be just changing the tension on the cable slightly by adjusting the screw on the shifter.  Put the bolt back into the shifter to keep water, dust and general crap out of the shifter, and sit back with a self-satisfied grin because you once more have a bike that will stay in gear.

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Tyres and Punctures

So you’re halfway round an epic trail, feeling like just maybe you’re starting to get the hang of this mountain biking thing, with adrenaline running, your legs flexing underneath you as you pump the trail… and suddenly the back tyre starts making a terrible sound and flopping all over the place.  Oh no!  Puncture!

Don’t panic.  First off, while riding on roads and cycle paths may tell you that a puncture is a rare thing, it most certainly is not.  This is mountain biking.  Impact punctures happen when you go over rocks.  Penetrative punctures (maybe that’s a little explicit… couldn’t think of a better word) happen when you ride over thorns.  Out on mountain bike trails, seeing someone sitting at the side of the trail with a wheel in their lap is pretty common.

So, what to do?

Repair or replace, basically.  Puncture repair is, in my experience, somewhat hit and miss, and requires a lot more time than you typically want to spend sitting beside a trail.  It’s possible, but by the time you’ve finished your hands will be cold, your muscles will be cold, you’ll be cold, and the adrenaline and endorphins that got you the last few miles will be long gone.

Much better to replace the inner tube, and repair the puncture when you get home.

Step 1: Turn the bike upside down.  Maybe it seems obvious, maybe it doesn’t, but grab it by the seat post and a fork leg and turn it upside down.  I understand it’s not considered to be the best way to take a wheel off, but it’s most certainly the easiest, particularly when you’re in the middle of a muddy trail.  Put it off the trail somewhere, don’t be the idiot who’s right in the way of everybody else.

Step 2: Take the wheel off.  Pull back the quick release lever (or undo the bolts if you have no quick release) and twiddle it a couple of times anticlockwise.  If you have V or cantilever brakes, you’ll need to disconnect them, normally by pulling the end of the cable and lifting it free (at the brake end, not the handlebar end).  Lift the wheel out.  If it’s the back wheel, lift it a little way and then carefully lift the chain off the sprockets.  Congratulations, you’re now holding a wheel.

Pull back the quick release... also, clean your bike occasionally so that it doesn't look as disgraceful as mine.

Pull back the quick release… also, clean your bike occasionally so that it doesn’t look as disgraceful as mine.

Step 3: Take the tyre off.  If the tyre isn’t fully deflated, stick the end of a tyre lever on the centre bit of the valve to let the rest of the air out (with Schraeder valves – with Presta valves unscrew the end section and push it in).  Then stick a tyre lever between the bead at the edge of the tyre and the rim of the wheel and lever the tyre outside of the rim.  Use the other tyre lever to gradually work your way around the tyre until one side of it is completely free from the rim.  Then stick your fingers into the tyre, push the valve out out from the hole in the rim and into the tyre, and then lift the inner tube completely out of the tyre.

Stick a tyre lever between the bead and the rim...

Stick a tyre lever between the bead and the rim…


… work a second tyre lever around the rim…

... until the tyre is completely off on one side, and you can lift the valve out of the rim and pull the tube free.

… until the tyre is completely off on one side, and you can lift the valve out of the rim and pull the tube free.

Step 4: Keep the inner tube as it was in the tyre, and find the puncture.  Once found, investigate the tyre itself for any thorns or stones or nails or anything that might have caused it.  You should always run your fingers around the inner surface of the whole tyre anyway, but knowing where the puncture was will help you to know where to look first.  Remove anything that you find.

Run your fingers around inside the tyre...

Run your fingers around inside the tyre…

Step 5: Put a couple of pumps of air into the new inner tube (just enough to give it the beginnings of shape), and push the valve through the hole in the rim from the tyre side.  Gently push the rest of the tube into the tyre, keeping it as straight as possible and pushing it far enough in to be clear of the tyre bead.

Step 6: Using the tyre levers again, lever the tyre bead back inside the rim.  It should work in very easily most of the way round.  Be careful not to pinch the inner tube between the bead and the rim.  For the last little bit, you’re technically supposed to forgo the tyre levers and pull the tyre back into the rim by hand to avoid pinching the tube, but personally I always find that next to impossible.  So, carefully use the tyre levers to pop the whole tyre back into place.  Make sure the valve is straight (you can still straighten it a bit by manipulating the tyre with your hands), and pump the tyre up most of the way.

Step 7: Put the wheel back on the bike.  Some points that sound obvious but are remarkably easy to forget: the sprockets need to be on the chain side; ideally the chain needs to go back onto the sprocket it came off; the brake rotor needs to sit back neatly between the pads of the caliper (if using disc brakes); the axle needs to firmly back where it should be.  Then tighten the nuts or quick release lever up again (this can take a bit of messing to get right), push it back into place, reconnect the brakes (if using V or cantilever brakes), and turn the pedals a couple of times to make sure it’s back in the right gear and you don’t get any nasty surprises when you’re back on.

Step 8: Try and get as much air out of the old inner tube as possible and then pack it away for later repair, or for repair and use if you’re unlucky enough to get another puncture on the same ride. Do not leave it littering the trail.

Step 9: Turn the bike right way up again.  It’s much easier to ride like that.

The above is the basic procedure for changing an inner tube.  As it turns out, it is a little difficult to describe things that seem quite simple at the time, but I hope it’s clear.  There are a lot of variations on bikes, and so it has been pointed out that there are an awful lot of exceptions to this procedure.  A clutch rear mech, for example, will complicate things.  I don’t have one, I can’t imagine most bad mountain bikers would, and I have no idea how to deal with one.  Sorry about that, you’re on your own on that one.  Tubeless bike tyres won’t follow this procedure either, but that’s because the basic procedure for them consists of ‘pull out thorn; pump up tyre’ and if that doesn’t work, spend a lot of money replacing the tyre.  However, for the majority of us, who have tubed tyres and quick release levers, this guide will work.

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