How To Bleed Any Hydraulic Bike Brake

most modern mountain bikes have hydraulic disc brakes on board which offer excellent power and consistency but to keep them that way a routine bleed will be needed from time to time so in today's video we're going to go through everything you need to know about disc brakes how they work all the things that can affect them and more importantly everything you need to know to bleed your brakes there are loads of different brands and models of disc brake available on the market each of them having slightly different setup options and slightly different variations on the way that you bleed them so in today's video we're going to be looking at all of them a bit of an overview so you can understand what it is you need to do to get air out of your system and to bleed your brakes thoroughly okay let's have an overview of a break just so you can understand what each component does now I've got a handy cutaway option here this one is a SRAM lever but the same things apply to many brakes on the market so starting with the lever ignoring the fact the clamp is missing on this one the clamp would actually look like this lever here so you have your lever blade I'm sure that's familiar to everyone and you have the pivot in which it moves around this one as you can see quite clearly has a bearing there you might notice there's a little dial on the top here this is the lever reach adjust so that's responsible for moving the lever in relation to the handlebars but not in relation to the piston on the inside so if you have big hands you can dial it to be far away small hands closer to the bars uh you won't always have a dial like this sometimes you have to access a small or a very small Allen key head hidden underneath you might also notice there's a little dial on here this one is for adjusting the bite points of the actual pattern it's like a micro adjust for moving the pads closer or further away from the disc rotor now not all brakes have this feature and the brakes that do have slightly different variations on the dial hope brakes for example have two dials that look like this one on the lever Shimano ones have a free stroke adjust which is actually a screw head on there now if I flip the lever around you're gonna be able to see the piston on the inside the Piston is what actuates the whole system so as you move the lever it pushes the piston and pushes the fluid down the line into the caliper at the other end you can also see if you look closely when I make the adjustment on the actual reach adjust it just moves that piston slightly so it just changes the position at the other end there the next thing to look out on the lever is the actual reservoir on the top here now if you look at this one on the side on you'll see underneath the cap of it there's a little rubber diaphragm now this is what makes the system an open system now all modern mountain bike disc brakes use an open system and it doesn't mean there's holes in there and you know rain and stuff can get in what it refers to really is the fact there's two little vent holes on the top here and the diaphragm with some room between the cap and the diaphragm itself as you use your disc brake heat is generated the fluid gets hot and will expand slightly so this is to allow as you can see here it moves around is to allow for fluid expansion and those holes literally just atmospherically allowing that to to do so without hampering the feeling of the break if those holes weren't there and the diaphragm wasn't there what would happen as the fluid expands it has nowhere to go so instead of having a lever that feels like this it will pump up and the lever will barely move next up is the bleed Port now most brake levers have a bleed Port we're going to show you a couple that don't have them a bit later on in the video and a bleed Port is quite simply your access point for getting fluid in and out of that system this Leaf actually has one on both sides because it's a what we call a flip-flop lever so you can use on either side of the bars accordingly and it means you'd have to mess around with it too much with bleeding but levers that are not a flip-flop design like the Shimano one or this trp one have a single bleed Port the last thing you need to know about is the hose attachment so your brake hose will go straight into the lever at this point and on the end of the actual hose itself you'll have a barbed fitting that goes into the end of the actual brake line and you have an olive attachment which is a compression fitting so you screw it into the lever it compresses so no fluid or air can go in or out at that point and then you have the caliper end so firstly you have your two Mount points uh which basically mount it onto the frame or to an adapter to allow for different disc rotor sizes next Point you'll probably notice will be where the actual brake hose comes into the caliper this fitting is known as a banjo fitting because it kind of looks like a banjo and you can move it to multiple positions to get really good routing for it next up looking from the top down you can see the actual pin that runs through here and the brake pads on the inside now if I flip it over you're going to get another view of those brake pads and the inside of the caliper so as you can see where the brake line comes in the fluid will go down these channels Behind These Pistons here which drive onto the actual brake pads and compress them at the bottom end you'll see there's a bleed Port the blue Port has the same channels and obviously you can flush fluid in and out in both directions in order to get good fluid in bad fluid out and get the air out no surprise there's going to be lots of places you can Harbor the bad stuff in there now when you look at the Pistons close up you've got little rubber seals around them those rubber seals need to be nice and lubricated as due to pistons in order to do their job correctly those little rubber seals are actually responsible for pulling the Pistons back like retracting them into the body and this particular caliper has four Pistons also known as four pots you can get anything from two Pistons up to six pistons on some model of brakes [Music] okay so where exactly can air get into the system given that it's a sealed system well you've got to start with the first things first when you actually assemble the system if it comes in different components air can get in at that point it can also get in when you trim the brake hoses down as you trim them down you have to fit this new Barbed fitting into the end and if you haven't trimmed the hose in exactly a 90 degree angle for a flush fitting of that barb fitting you guessed it air can get in and out at that point it has to be a perfect cut every time and of course you must use the correct compression Olive they all look very similar but they're all slightly different depending on the particular break you're using IF in doubt don't use it and double check because there's a lot of different orientations available on the market to suit different models of course when it goes to International brake lever itself it needs to be tight and sufficiently if there's any chance of a leak fluid can come out and air can get in there and then of course there's the bleeding process doesn't matter which way you bleed it whether it's a bucket and you're bleeding topped down down or syringes and you're bleeding bottom up you can push air into the system using those syringes and air can get in from the bucket if you haven't had enough male fluid in there you've not been paying attention when you're bleeding the system air conditionally get straight in there so it's down to you to make sure your system is as air free as possible now also don't forget there's loads of places that air can be harbored in the system as I've shown you with these custom ways look at the back of the Pistons here there's no suppliers you can find the occasional bubble tapped in there and I've known people that have sworn their brakes have been bled correctly but you manage to still get air bubbles out of them so sometimes you do need to bleed several times unfortunately some brakes can be more prone to it than others but a bit of persistency will pay off for you and the same goes for the lever bleed as well now something to bear in mind with the levers in particular when you're doing the lever bleed is your bleed Port is in a different position in different brakes even from the same manufacturer can be a different position you have to make sure the reservoir is underneath where that Port is otherwise you're not going to get a good bleed and it will still Harbor some air in there so do take care certain breaks like Shimano for example suggest that you run the brake lever about a 45 degree angle initially but then when you're completing the lever bleed you actually move it backwards and forwards a couple of times just to make sure there's no air in there and the last two things you need to factor in of course with air in the system is perished seals so if you've got a DOT fluid brake for example and it's not been ridden for some time a it will have ingested moisture in there and the moisture can damage the seals and cause corrosion on the inside all sorts of stuff so old brakes generally will need a bleed to make sure they're working nicely again and then if you've been hammering your bike and you've boiled the brakes you will have air bubbles in the system because as it vaporizes you'll get some tiny air bubbles present and that nice firm feeling break from compressing hard fluid on the inside there turns into a mushy horrible break where you're compressing Air instead I'm sure we've all felt that at times [Music] okay to bleed your brakes you're going to need a bleed kit now the obvious thing would be to have a specific bleed kit for your brakes I a SRAM bleed kit if you've got Saran brakes or a magura kit for magura brakes but you can get overall kits that will suit multiple different brakes with different fittings and attachments the most important thing that you take into account whichever kit and whichever way you're going to do it is that you have one that suits the correct fluid so there's two major systems you get dot fluid and you get mineral fluid and neither are compatible if you have a bike that has dot fluid and also you have another bike that's got mineral you're going to need two separate sets of fluid and two separate sets of kits you do not want to mix these together at all and in addition to the actual relevant bleed kits for your particular brakes you'll need some protective glasses just in case none of the oils are good to go anywhere near your eyes for obvious reasons you want some protective gloves not only are they good to protect the skin your hands but actually help you a bit dexterity to actually grip some of the stuff when it gets slippy with the actual fluid as well and I recommend making sure before you start you've got the relevant Allen Keys Torx keys and any other additional tools that are specific to your particular system [Music] okay so the age-old argument with disc bracing is which fluid is better well the simple thing is I have dot fluid and mineral fluid and both of them are excellent choices for use in mountain bike brakes so whatever you've got you've got decent brakes so don't worry about that but the fluids themselves have slightly different properties and it's good to know about these just so you can act accordingly with your particular system in looking after and maintaining your brakes now let's have a look at DOT first or dot dot stands for Department of Transportation and that's because it's a regulated fluid it's used in a motor industry and it's regulated because it has to perform at certain temperatures both high and low so you could ultimately say that this is a very good high performance liquid now the issues you get with using dots are a is excellent for using on breaks however you do need to maintain it and it basically has a shelf life that comes with that so high performance but you do need to look after it accordingly now the fluid itself is hydroscopic which means over time through microscopic holes in the brake lines and anywhere else in the system it's going to ingest moisture and Dot fluid can actually ingest two percent of its volume in your system in just a year so it will need some care to make sure they've bled correctly this is also a reason why when you have dot fluid we always recommend having a small container rather than having a big Workshop spec one unless you're bleeding like hundreds of breaks at a time you want to have a small amount of this because the shelf life really is going to be around a year for something like this it will vary depending on the storage conditions how damp the room is things like that but ultimately if there's any moisture in the brakes that's what's going to affect them now dot fluid has a very high boiling temperature 270 degrees Celsius on average extremely high however that goes down to about 190 degrees Centigrade as soon as you get any moisture on the inside there so your brakes will be hampered if there's any interference with that so if you've got a bike for example that you've not ridden for some time that's got dot brakes on it there's a good chance you're going to need to bleed those brakes and has some fresh fluid in there now the fluid itself is slightly corrosive now it doesn't mean it's like a crazy acid or anything but what that means is it can be damaging to paint work on your frame it's obviously not damaging to the brake components it's also why we recommend wearing gloves and a pair of eyewear when you're actually working on the bike and next up mineral fluid now this stuff is not regulated now as a result you get loads of different variations loads of different types and each one is different so if you're going to buy Dot fluid for your brakes for example there tends to be four or five point one that you have in your matter what brakes you can mix them together and you can buy any brand they're all going to perform as stated mineral fluids all have slightly different things because it's not regulated now you could look at this and think well dot must be better because it's regulated not necessarily true the freedom that the designers have of working with the fluid is not regulated means they can have their own formula that is best suited to their seals their brakes their calipers their Pistons their entire systems so Shimano naturally will recommend using their fluid with their system Magoo recommends using their fluid with their system etc etc now the fluid boiling point does vary massively on Mineral fluid compared to dot fluid which as we know is about 270. so talking anything from 190 degrees Celsius all the way up to about 290 so a huge variety there but also is still going to be affected by water that's ingested into the system but it is a little bit different because this fluid is hydrophobic it's not hydroscopic like the dot stuff what that means is when water gets into the system it's not going to sort of get into the fluid itself it's actually going to pull separately the downside to this is it's going to pull at the nearest point which will be your caliper and of course if you've got water down at the caliper it's obviously going to boil turn into air obviously not ideal down there but the upside to that means it's really easy to get it out flush it out the system so not necessarily a bad thing at that point now one of the great things about mineral oil and why many Brands tend to use it is it doesn't go off as such but because it's hydrophobic it doesn't ingest moisture you can get a big Workshop spec one of these which is great values to have if you've got multiple bikes and you like to bleed your brakes and stuff the oil's not going to go off and it's also great if you've got various bikes or you don't ride that frequently your brakes are going to stay feeling good they will obviously need routine bleeding just like dot ones but it's not going to be quite so sensitive in terms of the fact that moisture gets in to affect the actual fluid itself and the last thing to take into account is mineral fluid is not corrosive granted you don't want to get this anywhere near your eyes you shouldn't get this on your skin and you need to dispose of it accordingly so all brake fluids no matter whether mineral or dots speak to your local recycling center and they'll tell you the quantities you can get rid of it and how to do so safely the bottom line is with both fluids with both dots and mineral is that they are both affected by fluid getting in the line it's going to degrade the performance of the brace you can end up with air in the system and inconsistent braking that is what you do not want to have [Music] okay so let's look at the fundamentals of bleeding a break because the the principle is basically the same for all brakes now there will be some slight nuances to each individual system that is slightly different and we're going to delve into some of the most common options on the market that you probably have on your bikes at home but first let's do an overview on bleeding a break preparation is key so the first thing you want to make sure you do is prepare your lever first now your lever will have some form of adjustment it might just have reach or it might have a bite point adjustment as well so if you've got a bike point adjustment you want to undo this you want to unwind it as much as possible and then the same goes for the lever reach adjustment no matter what the brand you're using back these things out you want to make sure that the lever can take the maximum amount of fluid to achieve a good solid brake bleed set your brake lever so the bleed Port is the highest possible thing of course the bleed ports are all in slightly different places depending on what the brands are and you've got to make sure that a reservoir is under the port it's not always that obvious sometimes to leave will be horizontal other times like this one would be about a 30 degree angle next up is removing the pads so remove the pin and make sure when you remove the pads you can't contaminate them so keep them separately away from any oils or any part of the bleed system next up you want to put your bleed Block in this basically stops the Piston moving so you can get the correct amount fluid in the system now you might need multiple bleed blocks depending on the model of brakes these magura ones you need two in place these ones from SRAM you need a single one in place now the sizing of these is different depending on the model and the brand so just make sure you have the correct one for your fitting and the last thing to do is get the correct fluid in your syringes make sure there's no air bubbles present in the actual tubes next up attach the syringe to the caliper and to the brake lever your particular brake might have a bucket design we're going to deal with a little bit later in the video your break could be a bleed from the top down to the caliper or it could be from the caliper to the top that's really the fundamental thing that changes between the different systems so again we're going to run you through the most common options out there next step is to pressurize the lever now if your system has an open bucket design on the top as part of the bleeding you want to hold the lever in place near the bar using a toe strap or something similar the idea is it pressurizes the system and you remove a small amount of oil from the system allowing the oil to pull back in again at the top so make sure you've got a really good firm lever if your system is using syringe at the lever end you actually create a vacuum to achieve a similar thing flicking the lever is very common at this point while the system is still open to remove any air bubbles that can be trapped in the lever and you might need to move the lever up and down depending on the model just to make sure you've removed any trapped air last steps are to close the system and give it a clean and if you need to repeat okay now for bleeding any break well there's loads of different brands out there we're going to deal with the major ones you're likely to see spect on bikes now of course there's lots of different models we're talking in general here and let's go with Shimano first now Shimano brakes use mineral fluid the usual method uses a bucket at the lever and a syringe of the caliper but you can use a syringe at both ends the bleed process is bottom to top and then back down and you pressurize the lever using a strap and opening the bleed Port quickly air can get trapped in the lever so it's advised to move the lever back and forth a few times just to make sure the air is removed SRAM brakes used dot fluid inside breaks from 2017 onwards used the bleeding edge bleed Port which is absolutely brilliant use the syringe at both ends and you bleed top to bottom closing the bleed Port before removing the bottom syringe makes this process very easy you create a vacuum on a top syringe to pressurize the lever magura these brakes use mineral fluid and they can use syringes at both ends or a bucket at the lever end you bleed bottom to top and then back down through the system you close the caliper and you pull the lever to introduce pressure and migrate any lever air bubbles out closing the system to finish hope breaks use dot fluid the usual method is to open a top reservoir on the lever and use a syringe at the caliper you bleed them top to bottom in the same way that you would with motorcycle brakes you top up the fluid in the reservoir and then you close the system at the end you can also use a bucket at the lever to make for easier filling the reservoir on the lever is quite small and you do need to monitor it when filling as if it runs dry you will directly pour air into the lines the bucket system means you can have much more oil available to you here to pull into the system trp these brakes use mineral fluid and there's two methods to bleeding them depending on the model you can have the bleed cup at a lever and the syringe at the bottom or you can have syringes top and bottom you bleed them bottom to top with a push pull style use a lever strap to pressurize the lever much like you would with Shimano and you open and close the bleed nipple at the bottom watching the fluid level at the lever Haze these brakes use dot fluid and use syringes top and bottom you bleed them bottom to top and then return back through the system you add the vacuum at the lever using the syringe and the newer models actually have two bleed ports on the caliper for a further bleed to ensure zero air in the system very cool and it also means that it's very good if you need to service the caliper to ensure a tight bleed [Music] okay and of course with all systems there's going to be a few tips and tricks and I'm sure many of you will have discovered your own individual tips and tricks that nothing to do with the manuals that just help you when you've got those air bubbles you can't quite get out the system here's a few that we tend to use here at gmbm Classic one tap in the hose get a spanner small one and just tap the hose when you're flicking the lever or sometimes when you're pushing the fluid through the system could really help especially if you've got any kinks in your brake line there that can help the air migrate through it obviously you want to make sure that the air has the best possible chance of getting to the top so if you have got any Curves in those cables and hoses make sure as straight as possible to help the air find its way out to the top always make sure your brake caliper is lower than the reservoir which is on the lever this is easy when you're doing your front brake but sometimes when you're bleeding your rear brake because the rear caliper is at the back of the bike the weight of your bike in the stand will actually move it and your caliper can end up higher than the actual lever this wreaks Havoc so just pay attention to that if you have problems with air in the systems and you you've got a bucket star system you can actually leave these open for some time you can strap the lever pull it to the bar make sure your caliper end is closed and you can leave the lever end open tap your way up the hose that you might just find just that one little annoying air bubble just migrates this way out by itself the good point about having the bucket there is as that air bubble migrates out fluid's going to replace the space it had on the inside of the line and the last one is your bite point adjustment whether you have a dial or something on your actual levers for manually adjusting it or it's an automatic system on yours it's going to be affected by the condition and how clean your brake calipers are so as with anything on the bike you should be cleaning them with your brake calipers think what's happening the Pistons are moving in and out the whole time if they're dried up and they're dusty and dirty they might not be sliding and retracting back into the actual caliper properly what you want to do is lubricate them now if your bike has dot fluid brace use dot fluid to lubricate them if your bike has mineral fluid brace you use mineral fluid what you want to do is literally just pull your brake lever just to expose those Pistons slightly take care you don't want them to pop out and just use a brush or something small just to get a tiny bit of oil in place and then push them back in place pull them out again push them back in place and you'll find that they retract the correct amount at that point it's one of the things you can do if your bike is suffering from the pads rubbing for example That's a classic sign that you've been riding for a long time and everything's a bit grubby it's not just working as it should do okay so a bit of theory a bit of practice a bit of information about disc brakes hopefully there's some points in this video that can help you understand your brakes and to get the best out bleeding them now all the breaks I've mentioned in here we're going to make refresh videos of each individual one so we're going to do a walk through on how to bleed those and of course there's going to be some other videos we've already made floating around down there somewhere as always leave us some comments leave us some feedback if you've got help or issues on particular breaks feel free to get involved down there and if we can't help you we definitely know some people that can uh thanks for watching the video and we'll see you in the next one Tara

Channel: GMBN Tech

Views: 365,781

Keywords: how to bleed brake, bleed bike brake, bleed hydraulic brake, shimano, sram, magura, dot fluid, mineral oil, bleed shimano brake bleed, sram brake bleed, hope, hayes, trp, gmbn tech, mtb tech, bike tech, mountain bike, Bicycle (Product Category), MTB, bicycle, gmbntech, GMBN, Global Mountain Bike Network, mountain biking, Downhill, XC, Cross Country, Enduro, MTB skills, bike skills, mountain bike skills, bike, bike riding, cycling, gmvn, Doddy, Қ, 4905, scany15, ᐶ, 1o, 1t, 1w, Ꮖ, ዝ, ꔇ, ፕ3, Ҫ, Ҷ

Id: EcKnAnZWkHo

Length: 23min 19sec (1399 seconds)

Published: Sat Dec 10 2022