Installing hydraulic disc brakes can be difficult without the knowledge or experience needed for proper setup. However, if you’re mechanically inclined, simply bolting them on isn’t very difficult; it’s having the correct tools, accessories, and the fine-tuning and adjustments that can prove challenging. That said, a bit of know-how and experience can save you a good amount of cash down the road. In addition, becoming comfortable with the operation of your bike and its components can add confidence in maintenance and ideally minimize the need for trailside repairs.
Proper setup and functional brakes are crucial for the safe operation of any bike, so when in doubt, have the bike and brakes checked over by an experienced bike tech before riding.
We’re unboxing the latest Shimano XT 4-piston brakes, but not much has changed in the last 4-5 years. During the installation, the biggest change you’ll encounter between the models is how the Shimano I-Spec mounts to the shift levers.
Tools Required to install Shimano Disc Brakes
Like any bike repair, an investment in the tools required is the first place to start; having the proper tools to do the job is key.
If you’re just looking to bolt on an 11-speed pre-bled disc brake, you can often get away with the bare bones:
- 5mm Allen (hex) wrench
- 4mm Allen wrench
- 8mm metric open end spanner wrench
- Torx T25 wrench or Shimano Center Lock Rotor or Lockring Tool (depending on hub and rotor type to install disc brake rotor)
- Clean rags or shop towels & isopropyl alcohol
If you need to shorten the brake hose, additional tools will be required. If you’re an enthusiast you’ll want to invest in these tools to have on hand. If you haven’t invested in a portable bike repair stand its nice to have as well. They’re practically a requirement for any legit home bike repair shop. Our pick for portable repair stands is the Feedback Sports ProElite Repair stand.
- Shimano Disc brake bleed kit and Shimano Fluid (the small one is fine for a few bleeds but we buy in bulk now)
- Hose clamps or Shimano brake hose cutter/insert tool or sharp cutting tool (we use a Park Cable cutter and it cuts a clean edge) and mallet
- 10mm metric combination open/ closed-end wrench (ideal size pressing pistons in though a tire lever or similar object can do the job as well)
- 2.5 and 3mm Allen wrench
- Zip ties
- Torque wrench (though admittedly I don’t use them that often)
- The Park Tool DT-2 Rotor Truing fork tool ($18) is a nice addition to a disc brake tool kit but not required
- Latex disposable gloves are also recommened
Installing the brake lever
With 1x drivetrains being the norm, the installation of the front brake is uncomplicated. Shimano brake levers feature a hinge that can open all the way up, though I prefer to remove the grips and slide them on. With bolt-on grips, it can take less time to slide off a grip than open the lever hinge.
The 2020 brakes come pre-bled but unattached to the brake hose, so we start by sliding the lever onto the bar.
If it’s a rear brake, things become slightly more complicated, depending on the shifter you’re pairing with, and whether or not you’re running an integrated brake/shifter mount.
I-Spec compatibility: are 12-speed Shimano disc brakes compatible with 11-speed?
For this article, I’m upgrading to the new Shimano XT M8120 4-piston hydraulic disc brake on a bike running an XT M8000 11-speed drivetrain. I’m planning to ride tomorrow, so before getting too far, I first took inventory to make sure I have all the parts, rotors, adapters, and tools needed for the installation.
The new Shimano XT 4-piston brakes are going on my Transition Sentinel with a Rockshox Lyrik fork, and the first thing I need to verify is whether the new brake from the 12-speed group is cooperative with the previous generation 11-speed i-Spec mount.
Turns out the new M8120 brake with I-SpecEV plays well with the 2015 M8000 I-Spec II shifter I have here, with a small tweak.
I’m running the XT brake from the 12-speed group with the 11-speed, and to pair them I simply unbolted the lever from the I-Spec II adapter and bolt it directly to the lever. As the bolt is a bit too long, I added two small washers to avoid scoring or damaging the bar.
Sorting out the different model year lever and shifter is probably the most troublesome part of the install. I’m running XT SL-M8000 2 and 4-piston brakes on several other bikes that all utilize I-Spec II. My DH bike runs the Saint 4-piston brakes that use the I-Spec B; fortunately, it’s not too hard to figure it all out. (need more info? See links below for additional resources)
If you’re running a different shifter, Problem Solvers probably makes a solution for you.
Installing the brake caliper
Check to be sure you have the correct adaptors on hand before starting. In my case, the Lyrik fork and Transition frame both use post mounts and can be used without that need of additional adapters when paired with 7″ / 180mm rotors.
Start by hand threading the bolts into the threads, and ensure they’re threaded correctly, then switch to an Allen wrench. Tighten the bolts temporarily, then back them off just slightly.
Assuming you’ve already installed the rotors, now install the wheel. Rotating the wheel, verify the rotor is true/straight before setting your final caliper adjustment. If the rotor has some slight back and forth movement you can true it by cold setting it (AKA bending) using a rotor truing tool (I have the Park Tool Rotor Truing fork DT-2 but you can also use an adjustable head wrench in a pinch.) If it’s a used rotor with a significant amount of side to side play, it’s generally easier (and your brakes will work better) to simply replace it and delegate it to the backup parts bin.
With the wheel installed, looking down at the top of the caliper, and view the space between the rotor and caliper. Grip the brake lever and squeeze it to extend the brake pads. Engaging the rotor centers the caliper over the rotor. While maintaining pressure on the lever, tighten the bolts to set the caliper adjustment.
How tight to tighten the bolts? Shimano recommends torque specs of 6 – 8 Nm for the caliper fixing bolts.
After tightening the bolts, spin the wheel to make sure the wheel spins freely and there is no drag on the rotor. If there is contact between the rotor and the pads, look to ensure the rotor spins true, the pistons are extending evenly, and verify the caliper is centered over the rotor.
Note: If you’re installing a used brake, and find the pistons are not extending evenly, remove the wheel and brake pads. Pump out the brake pads a few millimeters (not too far or you’ll risk a fluid leak) and spray the pistons with rubbing alcohol to clean them, then press them back in, being careful to ensure they stay even. If you have a sticky piston, you may need to work them in and out a bit until they are extending evenly.
Shortening the brake hose
The newest iteration of Shimano brakes come with the hose unattached to the brake lever. With previous models, you could install the brake and run them with the excess brake hose, then cut them to fit at your convenience. In the past, I would generally run mine on the long side, as I often reuse parts and swap them between bikes.
The process for shortening the hose doesn’t change with the new models, but the olive is pre-installed already. Cut the hose to your preferred length and usual then install the connector insert.
Insert the brake hose in the brake hose connection part and tighten the bolt with your 8mm spanner wrench; as you do this the olive expands to a press-fit and a tight seal. Shimano recommends 5-7 Nm of torque. Wipe off any fluid when you’re done and push the hose cover up.
When shortening a brake line, it often possible to do it without having to bleed the lever. When installing two-piston models, we’ll remove the wheel and brake pads then do our favorite trick before shortening the line. Squeeze the lever a few times to extend the pistons a few millimeters. Shorten the line as usual then press the pistons back in when finished.
Now we’re pressing the pistons back in. My favorite tool for this is the closed end of a 10mm combination wrench. It’s crucial you don’t damage the pistons and that they are pressed back in evenly.
Then we’re simply replacing the brake pads. If we’ve done our job right, once we pump the brakes a few times we’re set.
Bleeding the brake lever
If there is air in the line, you’ll want to bleed the lever. Fortunately, Shimano makes it super quck and easy for us to do, provided you have the Shimano Simple Bleed kit. To bleed the lever we just need the Shimano oil funnel and Shimano mineral oil.
With the stopper placed in the funnel, add a bit of fluid. Make sure the lever is placed higher than the caliper to ensure air rises to the lever. Rotate the brake lever horizontal and level as possible, then remove the bleed port screw and put it somewhere clean. Then thread the loaded funnel into the bleed port.
Once you remove the stopper, just squeeze the lever and watch brake fluid displace the air in the line. There’s always something uber satisfying about watching the air bubbles rise out of the system.
Tapping on the brake hose can help dislodge any bubbles stuck in the line. Once the feeling at the lever is firm and no more bubbles appear, you’re good to go. Replace the stopper in the funnel and remove it. Then thread the bleed screw back in and readjust the brake lever to how you like it.
Test ride: bedding in and burnishing the brakes
Before the brakes will provide full power, you’ll want to properly bed in the brake pads. The easiest way to do it is to coast down a slight incline while lightly dragging the brakes. Spraying the rotors with water or rubbing alcohol can aid in speeding up the process.
The Shimano XT brakes also feature a free stroke adjustment. As a rule, I run these threaded in. While they don’t seem to provide a lot in terms of adjustment, if you have an overly stiff brake threading this bolt out a turn or two can relax the pad point of contact.
Final check over
Before heading out for your test ride, set the brake lever angle as desired as well as the adjustment bolt for the reach. Do a final check to make sure all the bolts are secured, and add the caliper fixing clip for that bit of additional insurance.
Shimano includes a plastic circular clip as redundancy for helping retain bolts in the event the thread lock on the bolts doesn’t hold the bolts securely. They’re easy insurance, but checking bolt tightness is something a rider should do regularly; make it a habit to go through every bolt on your bikes regularly to verify all bolts are secured. If you ride bike parks or do a lot of shuttling, you’ll want to do this before every ride.
If you’ve touched the brake pads or rotors with exposed skin, be aware that any oil or grease, including the oils naturally occurring on your hands and fingers can affect braking performance. It never hurts to spray down the rotor with isopropyl alcohol and wipe it clean.
Additional tips & resources
- Don’t reuse the olive or connector insert. They are designed for a one time use, so if you’re shortening the line, make sure you have a fresh olive and connector insert on hand first.
- For some reason, Shimano makes two different lengths of connector inserts – 11.2mm (silver color) and 13.2mm (gold) depending on which brake hose you’re using. Make sure you’re running the correct insert; if you’re using the one included with new brakes you’re good to go.
- Always do your hose shortening from the brake lever
- Keep the brake pistons clean
Shimano Dealers Manuals & Resources: