Brakes
Author: andrew joseph, with lots of help and contributions from: mattbaddeley, James Calder (JimB), Matt Cope (hairy_hippy), grahamdickenson, owenfackrell, James Howard(scoobyuk), Sebastian Huckson (Bad_Moon_Rising), PhilOsman, Matt Page (Voltage), rmo79, Colin Turner (ColdTea), Mike Southworth (mikeandsouth), smiffy.Photos by: andrewjoseph, Damien, John (orbiter), Jon (jaycmoore), Joss ven den Heusen (VooDoochild), Matt (hairy_hippy), owenfackrell, Robert Edwards.
All writers, co-writers and photographers retain copyright of their respective material 2005
Hydraulic Disk brakes on front wheel
V brakes, seen here on the rear of a bike
Brake Types: by James Calder
There are three types of cycle brake in use today, they can be divided into rim, disk and hub/drum. Disc and rim can both be further divided into mechanical and hydraulic, and mechanical rim brakes can be divided again into cantilever and caliper (more commonly know as 'V' or opposing caliper) brakes.
Rim Brakes
Mechanical (Cable) Brakes
Cable Disk Brake
Cantilever Brakes
These are the brakes everyone remembers from their childhood. The lever pulls a braided wire cable that in turn pulls a pair of cantilevered arms (which are mounted on the forks or the rear of the frame) together.
Caliper ('V') Brakes
These are the rim brakes that most people are now familiar with. The lever pulls a braided wire cable that in turn pulls a the pair of opposed caliper arms (which are mounted on the forks or the rear of the frame) together.
Hydraulic Brakes
Hydraulic Rim Brakes
Hydraulic rim brakes have a lever connected to callipers by a hydraulic hose. When the brake lever is pulled, a piston in the lever is compressed forcing fluid into the calipers which pushes the pads against the wheel rim.
Hydraulic Rim Brakes
Hydraulic Disk Brakes
Pulling on the lever compresses a hydraulic piston (the reservoir) situated within the lever. Hydraulic fluid (mineral oil or DOT brake fluid) then travels along the hose and expands the pistons within the calliper pushing the brake pads against a rotor attached to the wheel hub.
Cable Disk
This brake type uses rotors of the same type as the hydraulic discs but the action is brought about by a cable from the lever. The mechanisms within the piston can vary though. Some are entirely mechanical, and some have a cable-actuated hydraulic piston (or pistons).
Hub/Drum Brakes
Despite a brief pro rider-only experimental foray by Shimano in the mid nineties, hub/drum brakes remain relegated to shopper/hybrid type bikes and as such are exempt from this article.
Open and Closed Hydraulic Systems: by Colin Turner
Hydraulic brake systems can also be divided into open systems and closed systems. The major difference in these two systems is that open systems allow for the expansion of the hydraulic fluid whilst the closed system does not. In practice this means that with a closed system, as the hydraulic fluid expands, the callipers are pushed closer to the rotor, this can cause the brake pads to rub on the rotor and in extreme cases the brake can become locked on. To combat this, the closed systems usually come with an adjuster knob. Essentially a plunger, the knob is turned to either move the pads closer to the rotor to combat pad wear or to move the pads away from the rotor in cases of hydraulic fluid expansion. The knob can also be used to fine tune the bite point of the brake.
With an open system, the expansion of the hydraulic fluid is handled by allowing the fluid to flow into an overflow area to maintain a constant volume of fluid within the active brake system. This means that pads remain a constant distant from the rotor no matter how much the fluid expands. In practice this leads to a very reliable bite point and consistent control of braking, however in extreme cases, if the fluid has cooled and shrunk within the system and the brake has not been activated, the lever may need pulling more than once in order for sufficient fluid to flow back into the system to push the pads.
Dot 4 and Dot 5.1 brake fluids are hygroscopic. This means they easily absorb water from the atmosphere. Water in your brake fluid is not good for your brake performance since it has much poorer qualities as a hydraulic fluid than the Dot fluids. This leads to symptoms similar to air bubbles when the fluid becomes hot. It is suggested that Dot brake fluids are only bought in small amounts since storage over time will allow water to contaminate them. The hygroscopic nature should also be borne in mind whenever bleeding the brakes or exposing the fluid to atmosphere. It is recommended that the exposure is kept short and performed in as dry an environment as possible.
Brake Pad materials: by Smiffy
extracts from mtb-wales brake thread discussing organic and sintered pad materials
The organic part of the name comes from the fill materials which are typically jute, cotton, wood pulp and other cellulose sources - these are bound together with a thermosetting resin which finishes cure in the early runs, hence why new brakes smoke and old ones do not. Many "organic" pads contain metal - see HOPE for example, this does not make them sintered, which is a different thing altogether and eloquently described above. If you're cooking them at home, avoid the fumes. Phenols, isocyanates etc. are irritants and can cause permanent sensitisation (asthma). I'd do it on the bike in the fresh air if you can, and have the extra benefit of de-glazing your disc at the same time.
Sintered come in many forms, too. From the Cu & brass ones on MTBs, through ferrous and onto ceramic containing materials depending on the heat expected ( and the size of your wallet )
Remember that the heat and the mud are doing two different jobs. On resin pads by heating you are finishing the curing process and prolonging the life by hardening the friction material, the mud is helping the pad surface bed to the disc. The way sintered pads are made ... means they've already been hotter than we're talking about here anyway.
It's the contents, which .... defines the manufacturing process. Organic referring to the cellulose content and sintered after sintered brass wire and floorsweepings or whatever is in them. On motorbikes they talk about resin/semi-metallic/metallic/carbon (not on MTBs yet!) which probably describes them better.
All Brakes
Cable and Hose routing.
Care needs to be taken when installing or working on brake cables or hoses. There needs to be enough 'slack' at the front of the bike so that turning the bars does not stretch, compress or pinch the cables. The routing needs to keep the cables close to the frame so they don't catch, either on you or trail-side obstacles, but not too tight that they rub on the frame. If the cables rub they can soon wear a hole through. To prevent this you can buy patches that help protect the paintwork and frame
Extra cable needs to allowed for on suspension frames, extending the suspension will pull on cables that are too tight. Allow an extra inch or two around these areas to compensate.
Cable Rim Brakes
Setup
These are the 'old style' brakes (though many people will jump up and down and gnash their teeth at me. I say "Chill" to these people). The technology and materials used for modern rim brakes are far from old fashioned though, as they have come a long way from the bike brakes I remember when I was a kid. Most modern rim brakes will be 'V' style cable actuated, with long arms pivoting around a frame mounted brake boss to push the brake pads against the rim.
To set up these brakes you need to consider the vertical position of the pads on the arms:
- Too high and the pads contact the tyre with the potential of rubbing through and bursting the tyre.
- Too low and the pads can slip under the rims and contact the spokes.
Neither scenario is particularly good for your health. The pads should hit the centre of the rim and should be parallel, i.e. the face of the pad must make full contact with the rim. The bolts used to secure the pads on the arms come with domed washers that will allow you to adjust position and angle of the pad in relation to the rim.
To help stop squealing when the brakes are applied, the pads should be 'toed in', that is, the front of the pad should be angled slightly so it hits the rim first, the action of the brake will then pull the rest of the pad into contact for full braking force.
On rim brakes when fitting new pads use a zip tie to hold the
pads against the rim so the you have two hands free for adjustments. To
set up the toe in use a small piece of card between the pad and rim on
the leading edge (this is the bit that would touch the rim first) doing
this should stop any brake squeal.
Cable Rim Maintenance
As the rim of the wheel is the braking surface, it needs to be kept clean for efficient, effective braking. Now it is pretty much impossible for a mountain bike to keep its rims clean so we have to put up with dirt getting under the brake pads. Unfortunately this increases wear of both brake pads and the rim so you need to regularly check both. It's easy to see when the pads have worn down but the rim needs close inspection.
Some rims have marks on them to indicate when it is close to maximum wear, others have none. Check the wear indicator before every ride, it has been known for a severely worn rim to explode during a ride. If the rim does not have an indicator, check for concavity, if the rim has a deep groove all the way around caused by the brake blocks, then it may be time to get new rims. Of course 'deep' is difficult to quantify, but if you are concerned, get a new rim.
The ceramic rims are slower wearing then the usual aluminium rims (they are also much more expensive!), but they will still wear down. so don't take these for granted either.
To help keep your rim as effective a braking surface as possible, wash it after every ride, ensuring that all grit is removed as well as traces of brake block compound. There is a special 'rubber' that cleans burnt on brake block rubber from the rim, and while you're there check there are no bits of stone embedded in the brake blocks themselves, this can wear dangerous groves in the rim in no time at all.
Brake Cable Cleaning
Periodically, inspect and clean the inner cables, a spot of thin lube may help to restore smooth operation. Unclip the noodle from the brake arm to allow 'play' in the cable run, then slid the outers off the cable stops and further up the cable than normal. This will expose the cable that is usually hidden from view. Give this a clean with some old rag (it can be a new rag if you're posh), rub some lube in the cable and replace the outers. Do this for all sections of the cable. To be really thorough, especially if the brake action is grunky (I just made that word up, I really like it!), you can replace the inner cable. Remember to clean through the outers thoroughly though, or the new cables will be grunky soon.
Cable Stretch
After being used for a while the brake cables will stretch, resulting in the brake lever coming back nearer and nearer to the handle bar before the brake begins to slow the bike down. You can improve the braking while out on a ride by screwing out the tensioner to take up slack cable. After doing this a few times you will not be able to do any more, the tensioner will fall out. Before that happens, screw the tensioner most of the way back in, then take up the slack cable at the brake arm.
Undo the clamp nut holding the cable, pull out some of the cable and re-tighten the clamp. You may need to adjust this several times to get the correct braking function back.
Changing Pads
When the brake pads wear down to the minimum recommended level, or they become contaminated with grit or stones, you need to replace them. This is an easy process (though it will be a long involved complicated business when you have little time!).
First, screw in the tension/barrel adjuster at the lever to give more slack to the system, then undo the quick release of the brake, or push the levers in and prise the noodle out of the holder. Using the appropriate tool (usually a 5mm allen key), undo the bolt holding the brake pad to the brake arm. Take careful note of the arrangement of washers and spacers so you can replicate the current setup. Take out the old pad, put in the new pad with the same arrangement of washers and spacers, tighten up a bit so as to hold the whole lot together, then align the pads with the rim as mentioned above.
This process can be reduced in time and effort if cartridge pads are used. This system uses a pad holder that can stay on the bike when the pads are replaced, just take out a little clip or pin that holds the pads in, slide old pads out, slide new pads in, replace clip/pin. Job done.... oops, not quite, remember to adjust the barrel adjuster you loosened to give proper pad rim distance and so efficient braking.
guys if u really must have v's, go for any of the avid range.
from working in a bike shop tell me tell ya that avid brakes are by far
the easiest to maintain and great power. try to get hold of a pair of
arch rivals, I'm not sure their still made, finished in 2001 but check
chain reaction cycles, they'll probably have some.... if u have to go
Shimano go for the Deore ones.... hope this helps
I vaguely remember one of the mags suggesting a zip-clip
around the diagonally opposite pivots on the parallelogram part of the
linkage. The theory being that the squeal develops as the pivots wear
and vibrate - the zip-clip just preloads the bearings slightly and
stops them vibrating. Never tried it myself, though.....
Hydraulic Rim Brakes
Setup
These brakes act on the rim in the same way as cable rim brakes, with the same or even greater concerns over rim wear due to the extra force the hydraulic system can generate. The hydraulic system transfers and increases power from the levers, via a reservoir of hydraulic fluid, through flexible hose to the pistons near the rim of the wheel. As the lever is activated, fluid pushes out the brake pads to contact the rim, slowing the wheel.
Hydraulic rim set up is largely the same as normal rim
brakes. The pad should hit the rim straight on and not hit the tyre or
go into the spokes. A little bit of toe in is also useful and can be
done by rotating the whole piston in the clamp that mounts it to the
fork/frame. This is the same way that you set the general position of
the pad/piston. You can wind the pads in and out a bit with an adjuster
at the lever (on HS33s) to adjust for pad wear.
Key things for people to note when setting up this type of
brake is that the angle, toe in and closeness of the pad to rim are all
adjusted by loosening the two allen bolts (or allen bolt and quick
release lever on one side) and moving the whole piston in or or out and
angling it as required. There is a wedge shaped washer between the
brake boss and the brake body to help with toe in, but its fiddly to
use. The other key is the black plastic arm which presses against the
fork (or chainstay) to stop the brake rotating around the brake boss
bolt when in use.
Hydraulic Rim Maintenance
Less fiddly to maintain than cable rims, as there is no cable. You still need to check for pad contamination with grit etc, as these can really grind through the outer wall of the rim.
As with hydraulic disks, brake fluid deterioration or leaks causing air contamination will cause loss of effective braking. Bleeding to renew fluid or purge air is necessary from time to time.
I have a disc on the front and an HS33 on the back. The feel
of the lever is excellent, the power is excellent, and when it's set up
it's a great improvement over a v-brake. However, there are some
downsides that I have noticed:
-
The Pads are quite expensive (£15 for 4).
-
Mud clearance isn't as good as V-Brakes
. -
The set-up is an absolute nightmare, especially for the first time.
-
They weigh a bit more than v-brakes.
-
Getting the wheel out (especially the rear) can be a bit of a pain, even with the "evolution adaptor", though is not too bad, just watch you don't lose the washer!
Good points:
-
The on the fly adjuster is very good, especially if you have a slight buckle or want to quickly wind it in for a big down hill section or for pad wear.
-
The lever is easily reach adjustable and is comfortable to use.
-
The Pads are very easy to change and once set up are very maintenance free.
-
Available in a wide range of colours ! (mine are silver/grey).
Cable Disk Brakes
Setup
Setup of cable disk callipers is the same as for hydraulic disk callipers, centering the calliper over the rotor is the main priority. Setting up disk brakes is relatively easy, I will concentrate on the calliper as siting the levers is personal taste, though consideration of hose routing is also important.
The calliper needs to be centred over the rotor, the use of various sized washers helps to get this right. You may need different thickness of washers at each calliper bolt to get the spacing even, you need the calliper to be square to the rotor not the frame.
You may notice a small amount of warp in the rotor, i.e. parts of the rotor will come closer to the pads as the wheel is turned. As long as it is not too warped then it can be ignored. If the rotor is making contact with the pads for more than a 'light touch' then you may need to straighten the rotor.
Maintenance
Much the same as both cable rim and hydraulic disk. You need to watch for cable friction and cable stretch and also look out for pad wear and contamination.
What you need to do on maintenance is wind the pads in a
couple of clicks as they wear down. and keep an eye on the cable
tension. other than that the cleaning is the same as for hydro disks.
Hydraulic Disk Brakes
Post Mount & IS
Before I start talking about hydraulic disk brakes in detail, I thought it might be useful for you to know that there are two non-compatible brake calliper mounting systems available for front disk brakes: Post Mount and IS (Industry Standard). Rear disk brake mounts are all IS as far as I know.
Post Mount has the mounting holes in line with the fork leg. (found mostly on Manitou forks but other manufacturers are starting or considering using it)
The IS system has the two mounting holes perpendicular to the wheel.
Adaptors are available to allow use of IS callipers on Post Mount holes and vice versa. The Post Mount system does not rely on shims (thin washers to you and me) to centre the calliper over the rotor, instead it has an horizontally elongated mounting hole to allow fine tuning of the calliper. Some systems allow vertical adjustment as well for really precise mounting options.
Setup
The same consideration to calliper setup need to be borne in mind as for cable disks above.
On the disk brake set up there is a growing number of
manufactures that are doing the same as avid and suppling the calipers
as post mount with IS adapters so that to centre the caliper all you
need do is tighten the mounting bolts finger tight then pull the lever
and then tighten down the bolts.
Hydraulic Disk Brake Maintenance
While hydraulic disk brakes take away the worry of rim failure associated with rim brakes, they are not 'hassle free'. As mentioned above they have to be aligned properly to work effectively and they need regular attention to ensure they are safe to use.
The first and most obvious of things to check is, 'are the brakes pads in the calliper'? Now this may sound silly, where else could they be? But forum members have discovered, to their utter astonishment, that the pads have fallen out whilst riding along. This discovery has caused certain bodily functions to work inappropriately and initiated tremendous embarrassment. So to save having to bin your shorts, check the pad retainer system regularly, even religiously!
Some systems have a bolt and wire clip, some have a split pin. whatever system you have, make sure it is secure and make sure you know how to replace it properly before you go out on the trail. Discovering you don't know how to change your brake pads half way around a ride is going to result in a walk.
Changing Pads
When you notice the pads are too worn, either through your religiously regular inspections, or through a funny squealing grating noise when you apply the brakes, it is time to replace them. This is usually a fairly easy job.
Take the wheel off the bike, this makes it easier to see the brake calliper and gives more room for manoeuvre. Undo the retaining mechanism (remove wire clip, remove pin) and put them safe. Depending on the brakes, the pads lift out or drop down, remove them and inspect carefully. If one pad is worn more than the other then you may have a 'lazy piston', don't panic, there is a solution!
You will notice that the pistons are proud of the calliper body, this is because they have been pushing out further and further as the pad material wears away, keeping the same power and bite point at the lever. However, if you are putting new pads back into the calliper you will find there is now not enough room. So you have to push the pistons back into the calliper. Use a tyre lever or something relatively soft bodied to do this, so you don't damage the piston.
Push the tyre lever into the calliper and press the pistons back in, it can be quite fiddly and awkward and may need a lot of strength. You may find it easier to take the calliper off the frame to give you more room. To do this undo the mounting bolts, do not undo or loosen the calliper bolts or the hose! While the pads are out, you can clean around inside the calliper using water and a small brush.
Once the pistons are flush in the calliper, replace the calliper on the frame (if removed) and put the new pads in place. Replace the wheel and check everything is lined up properly.
use an old set of pads and a screwdriver to push the pistons
back in. It doesn't matter when you mangle the pads then
Lazy Piston
If you find you still have a lazy piston (one pad hitting the rotor before the other, the 'slow' piston is lazy) you need to work on this a while to free it up. If you can leave the wheel in place all the better. What needs to be done is to hold back the piston that moves furthest and hits the rotor first whilst allowing the lazy piston to move further out. So, using a screwdriver, hold back the 'fast' pad while pumping the brake lever, more fluid goes into the lazy piston and pushed it out further. This may need to be done several times to get the alignment right. You are looking to get both pads hitting the rotor at the same time without pushing it one way or another.
It pays to take the pads out and inspect them occasionally, as with rim brakes, grit can embed itself in the pad material and score the rotor. This is not usually so dangerous as on rim brakes but it can reduce braking efficiency and lead to rotor damage.
hold the old pads back with the screwdriver, so as not to
mangle the new set.
Bleeding
Hydraulic brakes need bleeding if air has been introduced into the system. Hydraulic systems work by converting the force from the lever to force at the brake pad via a liquid that does not compress. Air is a gas that does compress. If there is air in the system, then the air is compressed when you pull the lever, robbing the brakes of power. Bleeding purges the air as you introduce new fluid.
It is recommended that DOT hydraulic fluids are replaced every few years or so as the fluid degrades with use. Mineral oils have a longer working life but they too should be renewed regularly for optimum brake operation.
When I fitted Mono Minis to my Global I bled the brakes on a
workstand - with the calliper mounted higher than the reservoir which
really seemed to help prevent any air gravitating back up the hose when
you stop to refill the reservoir. Very quick and easy to do and has
been rock solid since.
Floating Rotors: by James Calder
For some hydraulic brake systems as standard, and for some others as aftermarket accessories, floating rotors are available.
Floating rotors feature a steel braking surface mounted onto an aluminium spider. The benefit of floating rotors is that as steel and aluminium have different thermal coefficients (i.e. they gain/lose heat at different rates), when the steel braking surface heats up, its heat is dissipated through the aluminium spider. This is useful because it means that a floating rotor will not becoming as hot as its non-floating equivalent. The fact that it will not be as hot has the obvious advantage of the fluid remaining cooler, but also means the braking surface is less likely to warp through the distortion caused by uneven heat-transfer that's suffered by non-floating rotors.
The floating moniker derives from the fact that the braking surface is attached to the spider via rivets that are interference-fitted to the spider, but not the braking surface. When the braking surface becomes sufficiently hot, it will have expanded enough that there is literally a (very) small amount of float between the braking surface and spider.
Cleaning Rotors
Rotors may need to be cleaned after maintenance or after washing, some cleaners may leave a residue on the rotor that reduces braking power.
I use pre-saturated isopropyl alcohol wipes to clean my
discs, they remove absolutely all residue, I think they are well worth
it.. I got them from ebay, but you can get them direct from this
seller.. rodger.middleton2@ntlworld.com he does them 100 for 12 pounds,
150 for 18 pounds or 200 for 24 pounds , all free post.
You can get alcohol wipes in any chemist too. Kitchen roll
with meths on also makes a good disc cleaner.
Warped Rotors
Rotors can be bent, often quite badly, during a crash or from overheating on a long descent, or from just trying to 'make it better'. They can be bent back into shape with a shifting spanner, you just need to be meticulous and careful. Make sure the jaws of the spanner are clean and oil free and have no nicks or bumps that can damage the rotor.
With the wheel still on the bike, rotate the rotor until you can see or feel where it touches the brake pads (putting a light coloured background such as a sheet of paper behind the brakes can help). I then move this back out about 90 degrees so it is well away from the calliper, slide the adjustable spanner down onto the rotor, tighten up and gently pull the rotor back towards the correct position. I do this a little at a time to ensure I'm not pulling too far the wrong way.
Rotate the wheel and check again. When the rotor does not rub against the pads at any point I leave it be. It may not be perfectly straight but it does not need to be. Even if it is dead straight, it won't stay that way for long as the heat generated by braking can warp it slightly anyway.
If the warp isn't large then it can be put back into shape
using just hand pressure. Hold the rotor firmly and push using your
thumbs in the direction you want the rotor to move. Its best to avoid
pushing on the rotor surface too much as it may contaminate the rotor.
If hand pressure isn't enough, try the spanner trick.
Mark the rotor splines with a marker pen (e.g. on mono minis
it will be 1-6). This makes it much easier to know which part is warped
and which parts to push back into shape.
Miscellaneous advice on disk brakes
'pump-up' - results in less effective braking, because the
lever goes 'spongey' and in extreme cases can cause the brakes to
lock-on (in closed systems, anyway).
Fade is different - it's when the high temperatures at the
disk effect the coefficient of friction between the disk and the pad.
One mechanism for this is contaminants (soap, grease, etc) in the pad
vapourising. As they come out of the surface of the pad, the gases
effectively push the pad away from the disk and it skims over the
surface like a miniature hovercraft. This is one of the reasons that
high performance disks (on any vehicle) have cross-drillings - it helps
cooling, but also gives the gases somewhere to go.
Copper grease the back of the pads, works on Hope so should
work on Shimano.
Ensure the disc mounts are faced properly too, a shop will
have to do that for you!!
If the pads are contaminated with oil/lube, this can cause
squealing. Baking the pads in a hot oven (honest) can boil-off the
contamination leaving the brakes hopefully squeal free. Other ways to
do this include holding the pads in the flame of a gas ring, giving
them a good going over with a blow torch or soaking them in petrol and
setting fire to them.
With Shimano own brand pads, the key is bedding them in
properly. Make sure you do 20-30 hard stops from high speed when you
first fit them and that will bed them in and make them last a lot
longer.. This can seriously make the difference between them lasting a
weekend and 5 or 6 months..
The End
This has exhausted my knowledge of brakes. For more advice sign on and visit the www.mtb-wales.com fora, the peeps there know more than me.
aj