Cool Tool Tuesday #9: The best setup and bleeding tools for hydraulic disc brakes
Everything you wanted to know about servicing your hydraulic disc brakes the pro way.
Everything you wanted to know about servicing your hydraulic disc brakes the pro way.
Welcome back to Cool Tool Tuesday! This edition continues our deep dive into tools for hydraulic disc brakes. The previous article looked at tools related to the installation of disc brakes, and this article covers all my go-to and favourite tools related to bleeding and setting up those fluid-filled stoppers.
If you’ve never aligned a disc brake caliper, replaced a set of disc pads, bled a brake before, or are unsure of the difference between mineral and DOT fluid, then your first stop should certainly be our complete FAQ to disc brakes.
As stated in the previous article, the Cool Tool Tuesday series is really aimed at those who either work on bikes for a living or wrench on personal bikes as a hobby. Very few, if any, of the tools mentioned here will be needed if you plan on letting someone else work on your brakes (no shame in that).
And given brakes are often all you have for stopping, hydraulic disc brakes are not a component you should be messing with until you have developed at least an intermediate level of mechanical aptitude. A bad bleed, a loose brake hose, or even just a wrongly installed brake pad can quickly put you and others at risk. Please be safe.
Alright, let’s begin.
Disc brakes are fairly robust in terms of staying clean, that is as long as you avoid contamination. Still, when it comes time for brake pad replacement or bleeding, it’s important to begin with cleaning the caliper. This is because the brake dust from pads will often sit around the caliper pistons, and pushing those dirty pistons back into their respective bores is a proven recipe for spoiling the seals that are responsible for not just keeping the fluid in the brake, but also for brake pad retraction and the automatic compensation for pad wear.
My first stop in the cleaning process is a quick blast from the air compressor. Nothing too direct or forceful, but just enough to blow off the worst of the dust from a distance. It’s never a good idea to breathe in fine particle dust, so take care when doing this (and also wear eye protection).
From there I pull the brake pads out and reach for the isopropyl alcohol that I keep in a refillable aluminium spray bottle. That spray bottle is commonly sold under a number of names; mine is a Vaper 19426, and it works simply by pressurising the canister with air through the Schrader valve at the bottom. By doing this the bottle works more like an aerosol, and I find it more targeted and less wasteful than the premium non-drinkable alcohol. A cheap household spray bottle works fine too, although it’ll typically waste more of the good stuff and this is Cool Tool Tuesday, after all.
With the alcohol still wet, I then reach for a Vikan 20 mm bottle brush (model #53763) that fits perfectly between most calipers for quick cleaning. These brushes are brilliant and the use of them for brakes was recommended to me by Troy Laffey of SRAM, who then provided the further tip to cut the metal shaft to a more appropriate length (the plastic handle is reverse-threaded in place).
For those not keen on a dedicated brush, you can use cotton swabs, floss with a clean lint-free rag, or use a fresh piece of lint-free paper towel (Scott’s Shop Towel for the win!), but again, this is Cool Tool Tuesday and the Vikan brush is great.
Speaking of Scott’s Shop Towel and isopropyl alcohol, that’s also the combination I use for cleaning up rotors (whether new or used) or as a final system clean before re-assembly following a brake bleed.
Replacing your disc brake pads doesn’t need to be a super involved process, but each brake carries a few unique quirks, and all will require you to reset the caliper pistons back into their bores (once they are clean).
There are a few specialist tools for pushing pistons back into place, and most allow you to do the process with either the pads removed or still in place. Pushing the pistons back with the pads installed has its perks by protecting the pistons, but it also slows things down given you should have pulled the pads out to clean those pistons.
My go-to piston press is a Pedro’s tyre lever. Flavour is personal preference – I prefer the Orange one, but the classic Lemon or Lime flavours are good too. The shape, the rigidity, and the fact it’s non-marring plastic are all just perfect for the role. And on the rare occasion where the gap in the caliper isn’t large enough for that lever, I use an older Park Tool TL-1.2 tyre lever (the narrow plastic one).
Alternatively, you can put the pads back in and use something like a Park Tool PP-1.2 or Unior’s 2-in-1 Disc Brake Tool (my preference given it doubles as a rotor straightening tool, although the straight handle occasionally limits caliper fitment). Such an approach means it’s almost impossible to chip an edge off a delicate ceramic piston (a Shimano-specific concern), but I find it also provides less feedback on how the pistons are (or aren’t) moving. These same tools can also be used without the pads in place, but again, I prefer a plastic lever for this.
Cool Tool Tuesday isn’t intended to be a how-to, but I will say you need to take great care when pushing Shimano ceramic pistons back into their bores. Push from the centre. Use light pressure. And it’s strongly recommended that you open the bleed port (or better yet, attach a bleed cup) at the master cylinder (lever) to ensure there’s no back-pressure against those pistons which can either make it easier to damage the pistons or force too much pressure against the master cylinder diaphragm (the bladder in the lever).
Not to hark on about piston cleaning too much, but both SRAM and Shimano advise their dealers/technicians to perform caliper maintenance by first exposing the pistons to their maximum outward position. You can do this ultra carefully by squeezing the brake lever until the pistons protrude out to just before the centre slot of the caliper (where the rotor sits). However, before you do this, you need to know that going too far will result in a waterfall of brake fluid followed by a piston on the floor.
A far less sketchy way to do such piston cleaning is to block the caliper in some way that lets you safely walk out the piston/pistons to a set depth. A sneaky trick I’ve seen from some SRAM employees is to stack two brake rotors against each other, which happens to be the same width as the centre cut-out in the caliper. I replicated such a thing with my 3D printer, because, well: nerd.
Meanwhile, Shimano officially recommends that you get its regular yellow bleed block for the respective caliper, and then hacksaw off one side while leaving the centre tabs in place. No, I’m not joking. Thankfully there are more elegant ways, such as VeloClub member Chris Heerschap’s 3D-printed Shimano piston exposure tools – a simple idea done well and certainly in the vein of Cool Tool Tuesday.
Whatever brand of pistons you’re pushing back, be sure to follow the manufacturer’s instructions as per the exact process. Some brands request that you add fluid to the system as you walk out the pistons for cleaning. A few brands recommend you lube the pistons with their respective brake fluid. Others suggest grease. Some say lube just collects grit. However, all manufacturers seem to agree that basic cleaning before replacing pads is a good idea.
A further quick thought on Shimano brakes: the small slotted brake pad retaining screw found on road brake calipers is known to strip out if you even make eye contact with it. Personally, I typically use a PB Swiss Slotted #2 screwdriver for these screws and the parallel tip design has never failed me (although the PB #3 and #4 sizes fit even better!). This is something I also mentioned in part one of my building a cycling tool kit series.
I covered the topic of rotor replacement tools in the previous Cool Tool Tuesday. However, I didn’t discuss the need to keep a check on rotor wear. A worn rotor is a thinner rotor, and it’ll cause the pistons to be used at a more exposed depth than they’re designed for. Push that rotor wear further and, eventually, it’ll just turn to pieces.
Rotors typically wear unevenly, and the best tool for measuring such uneven wear is an external micrometer that lets you accurately measure the rotor at specific points, namely at the centre of the brake surface. A thickness gauge is a comparable and lower-cost option, with examples including the Igaging 35-MT1 or IceToolz Rim Measuring Tool (originally designed for measuring rim brake wheel sidewall thickness). By comparison, a regular vernier or digital caliper has flat jaw faces and will only be able to measure the thickest part fitting in between those long jaws. It’s for this reason that I don’t recommend tools such as Birzman’s Rotor Wear Indicator, or the same idea sold by X-Tools, which assume the top lip thickness is the same as the rest of the rotor.
There are also ways to convert common digital calipers to measure off a specific point. A good example is Park Tool’s recently released DCA-1 which bolts onto the jaws of most calipers.
Now for the fun part: bleed tools.
I’ll preface this by saying that bleed tools are somewhat like hex keys, peanut butter, and coffee – every mechanic will have strong opinions about what’s best. Quite a few experienced mechanics have their own tricks for bleeding certain models of brakes which often involve competing brands or subtly customised tools. What I mention below is simply what I’ve found to work well for me.
If you’re new to brake bleeding, then the most critical lesson to know is that there are two common types of brake fluid that absolutely must not be mixed in any form. Shimano, Magura, TRP, Tektro and a few others use variants of mineral oil. Meanwhile, the likes of SRAM (or older Avid), Hayes, and Hope (typically) use DOT4 or 5.1 from the automotive world. You’ll need separate bleed kits for mineral oil and DOT brakes.
Secondly, there is no industry standard for how these bleed kits attach to the brake system. In fact, a few popular brakes require proprietary tool fitments (such as SRAM’s Bleeding Edge calipers). You may be able to re-use the syringe between a Shimano and Magura brake, but the required fittings are typically different. If you work on many different brake systems, then universal kits (one for Mineral and one for DOT) are worth considering, otherwise, just match the kit to your brake system.
Bleeding a disc brake typically requires a few general-use hand tools, such as hex keys, small Torx keys, and/or small metric spanners (often sizes 6, 7, and 8 mm). I’ve covered such things before. You’ll also want hand and eye protection, regardless of whether you’re bleeding mineral or DOT-fluid brakes. And of course, you’ll need a suitable bleed kit and the right fluid.
For those on a budget, you’ll be happy to know that quite a few of the low-cost and generically branded bleed kits will typically let you achieve a high-quality bleed (seek out options with metal fittings). After all, these kits are typically made up of a couple of medical-type syringes, some short sections of hose, and a few little threaded adapters. Brands such as Epic Bleed Solutions, Bleed Kit, EZMTB, and similar create functional kits that are perfect for the home mechanic.
In some cases, you can also DIY the bleed kit. For example, older Shimano brakes could easily be bled with a generic 20-50 ml syringe, a short bit of matching hose, and the correct fluid – effectively what their consumer bleed kit offers. The syringes can be the tricky part, as many will offer rubber seals that tend to swell up from the brake fluid and become useless over time. For this, I’ve found wholly plastic syringes to be a good option (Magura offers such things for not much money).
If you’re taking the DIY route with Shimano brakes then you’ll likely need to spend a few dollars on a bleed cup that threads into the master cylinder. The Shimano SM-Disc is the basic version and fits just about all current Shimano MTB brake levers, while most newer road levers can use that same cup by simply adding the cheap Shimano STR Funnel Adapter which converts the bleed cup from an M5 to a M7-size thread (some stores may even give you one for free if you ask nicely).
Those pre-assembled lower-cost bleed kits have come a long way, but there are things that set the budget options apart from the pro options. Durability, or more specifically, the consistency of holding an air-tight seal over repeated use is one of the main reasons to consider spending more. Meanwhile, some of those cheaper options can have you feeling like you need three or four hands to bleed a brake, while the more premium options typically offer features and hold securely enough to be used efficiently with just two hands.
Many of the brake brands produce their own bleed kits and they typically work admirably well. For example, SRAM’s Pro Bleed Kit was designed for the rigours of daily shop usage and features high-quality metal fitments, replaceable seals, and quality syringes. It’s a quality tool.
Shimano recently released a higher-end version of its Bleed Cups along with a new high capacity syringe that has a game-changing insert in the end of the hose that makes for an impressively easy and secure connection at the caliper-end bleed nipple. As my review of this new Shimano kit has already covered, the price of the fairly low-quality syringe is absurd, but that insert almost (almost) makes it worthwhile.
Meanwhile, the new cups are higher-capacity (great for gravity bleeding, where you let the caliper bleed itself of tricky air pockets from the top-down), they allow you to tip the brakes at more extreme angles without spillage, and the threaded section is certainly longer-lasting. Those new Bleed cups are also available in M5 (MTB) or M7 (Road) threaded versions. And if those aren’t fancy enough, then you’ll find full-metal bleed cups from the likes of Hope (M5 size) or small makers such as PinnerMachineShop – personally, I’d rather ruin a plastic cup than a brake if I cross-thread the thing, and I also like the translucent nature of the plastic cups – but each to their own. That said, I don’t just rely on a bleed cup for Shimano brakes. I’ll come back to this.
And then we come to the universal kits. Low-cost universal kits exist from the generic bleed kit brands mentioned above. The likes of AliExpress and eBay are full of even cheaper kits that will either work great or just greatly contribute to the world’s single-use plastic issue. The unknown is the fun of it, I guess.
I suggest buying from established brands or at least through retailers that you know will stand behind the product they sell. The likes of the previously mentioned Epic Bleed Solutions, Bleed Kit, and EZMTB are all solid options, especially for the casual user. Many of these brands offer different levels of kit, and spending more typically gets you metal fittings which is money well spent after a few uses.
The Park Tool kits carry an ultra-high price (US$136 for DOT, or US$154 for mineral), but come with a number of high-quality threaded attachments, rebuildable syringes, a few universal bleed blocks (to keep the pistons in their bores) and a clever ‘third hand’ that holds a syringe for you. Overall I’d liken the quality of these kits to a universal version of SRAM’s Pro Bleed Kit, plus that fun syringe holder. I like them. I just don’t like the price.
Meanwhile, I’ve found Jagwire’s Elite kit (US$105) to be somewhat clunky in use. My least favourite element is the hose shut-off valves which in theory should be fantastic, but often feel too stiff to use one-handed. I also don’t like the use of plastic between the syringe and hose connection that’ll surely get a bunch of use, especially given the provided blow-mould case requires you to unthread the hoses from the syringe when putting the thing away. Thankfully Jagwire makes it easy to purchase spare parts for its kits.
And then we get into the truly Cool Tool Tuesday-appropriate factory-level bleed tools which are commonly based around an electric vacuum pump. Those air bubbles don’t stand a chance. Such pumps have become an increasingly common sight amongst specialist mountain bike suspension repairers but remain a rare sight for brake bleeding purposes – especially given that like regular bleed kits, these machines need to be brake fluid specific.
Tektro is the only bicycle brake company I’m aware of that offers such a thing to dealers (it’s mineral-oil specific). “Vaccum setup (I tried both an electrical pump and a hand-cranked pressure bottle) is way too much trouble. The problem is the interface, you can’t get a dependable seal, plus the setup time is just not worth it,” said Sweden-based expert mechanic Jon Lindgren (aka AngryBikeMechanic and common sharer of hilarious #yourbikehatesyou content on Instagram) of the fancy approach to brake bleeding. Lindgren has since returned to the tried and trusted methods based on hand syringes and bleed cups (he’s a fan of gravity bleeding).
I still choose to use SRAM’s Pro Bleed kit for SRAM brakes – it just works.
For Shimano, I truly like their new TL-BR003/TL-BR002 bleed cups and poor-value TL-BR001 syringe (simply because of that little metal insert). However, for full Shimano bleeds (especially road levers which hold pockets of air) I’ll typically finish with a syringe from the Park Tool BKM-1 kit (you can rig up your own syringe by finding a suitable M5 or M7 adapter) in order to add a gentle vacuum at the lever – something that certainly isn’t recommended by Shimano and as a result requires care.
Those struggling to have enough hands during a brake bleed should first consider what tools are keeping your digits occupied. If it’s a wonky connection to a Shimano Bleed Nipple then consider using the new TL-BR001 syringe or getting a small compression olive/washer to lock the hose over the nipple (something included with a number of universal bleed kits and Shimano’s official bleed kits). If you can’t reach the opposite ends of the bike at the same time, then get a bleed kit with longer hoses (a feature most of the pro-level kits offer). Or if you left the 7 mm spanner at the bench, well, that’s your own fault.
Alternatively, you can look to the syringe holder supplied in Park Tool’s kits for inspiration (something that seems to do as it claims but I typically choose not to use). If such a thing appeals, then you can achieve similar (but not as good) hands-free help by attaching the syringe to the fork leg or seatstay with a toe strap or Voile Ski Strap (or equivalent) – just be mindful of the paint (an issue the Park Tool design solves).
During the bleed process, you’ll also need a bleed block to keep the calliper pistons in place and stop you from over-filling the system. Most bleed kits will include these, and generally speaking, the respective brake brands do the best job of these for their own brakes. However, I will give another shout-out to VeloClub member Chris Heerschap, as his 3D-printed Shimano brake bleed blocks insert from the top of the brake calliper which is arguably superior to Shimano’s own method of going from the bottom.
OK, that covers most of what I wanted to say about bleed kits. I know there are some things I missed so hit me up in the comments if the above doesn’t answer the questions that keep you awake at night.
Pad distance setting is a process that resets the gap between the disc brake pads after the pistons have been pushed into their bores. It’s a process that some mechanics swear by, while others simply skip and let the rotor handle the task.
And while it’s up to preference, there are benefits to using a rotor gap/pad gap setting tool. The main purpose of such a tool is that you can test the brake system for function without having to put the wheel into the bike. Brake manufacturers also sometimes recommend doing this as the sometimes-thicker width of the tool progresses the pistons out more slowly and sets them at the proper spacing for the rotor.
Meanwhile, other mechanics like to use such a tool to be able to keep a close eye on how each piston is moving, and then be able to quickly reset them if it didn’t go to plan. Lastly, some mechanics use a piece of slightly worn (thinner) rotor which progresses the pistons out further and can help to produce a stiffer feel at the lever – just be warned that doing this will narrow the pad gap and make it harder to achieve a rub-free brake.
So what does a rotor gap tool look like? Well, the brake manufacturers typically suggest using their supplied travel spacer, the same plastic thing that you’d put in the brake to ensure you don’t accidentally squeeze the pistons together during travel when the wheels are removed. Always make sure these are clean before you use them.
Meanwhile, Hayes has long offered its Feel’R gauge tool which offers a bit of dummy rotor for this purpose. Then there’s the repurposed bit of old rotor turned into a tool that Brad Kelly popularised on his way to being the ToolBoxWars Champ on Instagram. And very recently, Park Tool came out with its version of such a tool (PS-1), something that’s a little different as it also happens to be strong/stiff enough to be used as a piston press, too.
I own all of the above, and personally still prefer to use the Brad Kelly style of tool (pictured as the bottle opener above), namely because I have it on an offset handle that more easily clears problematic frame/fork designs that keep the caliper more hidden. I also keep a few different thicknesses of old thinner rotor around to help progress out the pistons further, a useful trick on first-gen Shimano road disc brakes that typically have levers pulling close to the bar.
So the brake is now on the bike, those hoses are a good length, and it’s filled to the brim with fresh and air-free brake fluid. It’s time to get that caliper aligned and rub-free. The typical approach is to loosen the caliper bolts, give the brake lever a squeeze, and then alternate between the two bolts (with tools suggested in part one) before the final torque is reached. This works, some of the time.
In other cases, you’ll do the above trick and then immediately hear brake rub; the sound of frustration. This is a topic that really needs its own detailed how-to guide, but this article isn’t it. At the simplest level, you want to start with a brake that can be set perfectly perpendicular to the rotor, and this requires a faced brake surface. You also want all the pistons moving evenly when you pull the lever. Those two things together should allow the above technique to work in your favour.
Failing that, there are caliper alignment tools available. The most common of these is the Hayes Feel’r Gauge style of tool (widely copied these days as evident by a number of Instagram and YouTube ads that’ll have you thinking it’s a groundbreaking innovation by a brand you’ve never heard of). This tool is effectively just two pieces of thin metal (like a feeler gauge from the automotive world, hence the name) that you insert over the rotor and slide into the loosened caliper. From here you pull the brake lever, and tighten the bolts. I’ve used this style of tool for well over a decade, which I feel makes me pretty well equipped to say that it only rarely offers a solution to the root cause of any alignment issues.
Personally, I often have more success with fussy brakes by using pristine out-of-date paper business cards (cards with current details work too, but that’s wasteful). Here I’ll insert the fresh business card (also good for figuring out headset bearing angles) into the rubbing side of the caliper, squeeze the lever, and tighten the caliper bolts. This technique helps to shim the rubbing pad/piston out, giving it more wiggle room when you next pull the brake. It doesn’t have a 100% success rate, but I find it more reliable than the caliper alignment tool mentioned above. An actual feeler gauge can of course be used for this, but you want to be sure it’s clean and free of oil.
Huh, I guess I just recommended not having a tool in Cool Tool Tuesday. Sorry about that.
Hearing an inconsistent rubbing at repeated points in the wheel’s revolution suggests that your rotor is out of true. It’s very common.
The old-school way of truing a disc brake rotor involved using a shifting spanner set to the right width. You slip it over the rotor where it’s bent and rubbing the pad, and then you give it a little bend in the opposite direction. This method still works perfectly fine, and as long as you’ve cleaned that jaws of the shifting spanner, you won’t get any judgement from me (but if those jaws are greasy, boy will I judge you and hold it against you until the end of time). Meanwhile, the new-age version of this involves a Knipex Pliers Wrench, one of my favourite universal problem-solving tools.
That adjustable spanner or Pliers Wrench method works, or alternatively, there are a myriad of dedicated tools for the job of tweaking rotors into alignment. And somewhat amusingly, pretty much all of them are based around some variant of a small slot that’s the width of a rotor.
There are of course some differences. Park Tool’s DT-2 was one of the first commercial options and hasn’t changed since. It offers a long slot for slipping down the spline of the rotor. And then at the opposite end is a short slot for just tweaking the edge of a rotor or giving one of the rotor arms a twist. Quite a few tools copy this shape.
Meanwhile, some newer tools now offer different-thickness slots to suit the changing landscape of rotors that now commonly vary between 1.8-2.3 mm in thickness. Abbey Bike Tool’s latest Stu Stick has such a feature, and so does an adjustable wrench/Pliers Wrench.
You also have the likes of Unior’s 2-in-1 which doubles as a piston press (a neat idea). Wolf Tooth and many others have worked out that your rotor truing fork should also open a beverage. Meanwhile, Pedro’s flare nut hose wrench has a slot for truing rotors. And you’ll find other variants, including multi-tools with such a feature, too.
Personally, I typically use a piece of fresh Scott’s Shop Towel (there it is again). Right now you’re probably imagining some kind of masterful origami technique, but sorry to disappoint. The paper towel simply serves as a guaranteed clean barrier between my potentially greasy/oily thumbs and the clean rotor. Yep, I just gently coax the rotor into true with my thumbs.
You can also re-use the above-mentioned business card for this. This technique is something closely aligned to what Aussie master-mechanic Brad Kelly does, and he’s like the Aussie Yoda of modern bicycle mechanics (seriously, Kelly’s Instagram account is a gold mine of proven old-school and creative new-school tips).
We’re almost done, I promise. I just wanted to give another shout-out to hex-based screwdrivers, something I’ve strongly recommended in previous Cool Tool Tuesday editions.
This is a tip that’ll prove most beneficial to those with new SRAM hydraulic road levers where adjusting the lever reach setting screws can be a little tedious without the right tools. A long and straight blade 2.5 mm hex screwdriver is the perfect tool for reaching into those recessed lever setting screws and dialling in the fit (as it is for derailleur limit screw setting). My go-to for this is the PB Swiss 8205.2,5-90. There are other companies, but make sure it has a blade with a consistent diameter throughout (most don’t).
So there you go, the second part to everything related to hydraulic disc brake tooling. If you’ve got a question then please reach out in the comments.
Cool Tool Tuesday will return in a few weeks once I’ve finished calibrating my torque wrenches.
Note: A number of the tools mentioned in Cool Tool Tuesday are not sold through traditional cycling channels and can be hard to find, which is also kind of the point of the series. Access to the tools covered will be easy for those in Europe and the United States. Use a search engine to find the products mentioned.
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