Info and Service for SRAM Mountain Bike Disc Brakes

Jun 17, 2023

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The details on SRAM’s popular disc brakes, plus bleed and service

Disc brakes are found on virtually every modern mountain bike for their combination of braking power and low maintenance. There are two main styles of disc brake systems used on mountain bikes: mechanical and hydraulic.

This story focuses on the SRAM hydraulic brakes found on many mid to top-tier hardtail and full suspension bikes. SRAM’s brakes focus on delivering control for every rider in any riding situation (which can be best understood with the below graphic).

Level (V4): Level provides performance for XC and trail riders—from entry-level technology and components all the way through the top tier using more exotic materials.

G2 - Successor to Guide, G2 gives trail, enduro, and some gravity riders options at various price points and technologies.

Code - Code focuses on the gnarlier end of enduro, gravity, and E-MTBs. SRAM offers two models here.

SRAM designs its brakes to meet the specific performance needs of different mountain biking disciplines and rider types. Each brake platform offers various degrees of adjustment and customization, depending on price or bike brand specification.

SRAM used the below designation to help differentiate between key features and customizations.

For example, if your bike is a Specialized Turbo Levo Alloy with SRAM Code RE brakes, this means your Code brakes have tool-free reach adjust and are the e-bike-specific model.

Three features set SRAM brakes apart from other brands:

If you’re like me and are curious about what's going on underneath the hood. Here is a diagram to help visualize hydraulic fluid, its path, and how it functions.

When you want to brake, you pull on the lever, actuating the cam mechanism which is designed around a push rod to “pull” the lever piston fore and aft.

This changes the pressure within the system, forcing power and pressure to the calipers where the piston heads engage with your brake pads. Ultimately, causing engagement with the brake rotor to slow the momentum down.

The next part to consider when going through your brakes is the hose.

This has been specifically designed to withstand and transfer pressure and power through modulation.

SRAM primarily uses “open” brake systems throughout its product range. The brand also offers cable-actuated brakes that pair with most conventional cable brake levers.

While appearing and operating in a “simpler” fashion, the critical downfall of an open brake system is heat dissipation. Because the kinetic forces generated under braking are converted into heat, this eventually builds up in the brake caliper, heating the dot fluid, and causing it to become less dense. This results in a loss of braking power.

Larger than some open systems in terms of size, closed systems are more complex because of the additional reservoir that they are designed with. This reservoir allows three critical functions:

The choice of open-design brakes allows for reservoirs to trap any unnecessary air within the braking system by letting the bubble travel towards the path of least resistance.

Because of the open design, the bladder in the reservoir when under pressure will flex to accommodate this build-up of force instead of pushing the caliper pistons out. When the system is completely at its limit, known as Pump Up, a temporary release of the lever will allow the release to normalize within the system.

This allows for aspects push rod to advance or recede within relative position to the ports allowing for adjustable modulation.

Helpful things that make SRAM’s brakes stand out are the proprietary Bleeding Edge and Stealth-a-majig features. These make the process of hooking up bleed syringes to your brake lever and caliper super easy and less messy.

The Bleeding Edge tech uses a syringe with a specific set of input ports that connect to various brakes via a port on the brake caliper body and lever/hood.

The Stealth-a-Majig is a SRAM proprietary compression nut/plug that threads in a counterclockwise fashion when being mounted to the hose barb which allows for the fluid to pass and connect to the brake lever housing and caliper body.

Use this as a guide to the bleeding procedures. For a more accurate and detailed step-by-step, watch this video tutorial from SRAM.

📓 A great reference or starting point to familiarize yourself with the process is the SRAM procedure manual all of which can be found online.

🔧 Tools and equipment you’ll need:

🧻 Once you’ve managed to wrangle all your supplies and tools, prepping your station with extra disposable towels and rags is extra handy as it can get messy from time to time.

One important note to mention when filling both syringes, allow one to contain between 5-8 ml of fluid, while the second could contain between 3-5 ml to accommodate fluid within the existing system to escape/be exchanged.

2. With the syringes full of fluid, you will want to remove any air bubbles from said syringes in order to reduce the possibility of failure and having to re-bleed the system.

Make sure to remove your rear wheel, and grab a 2.5mm hex key or bit to remove the screw holding the brake pads in place. Please do not lose that pin as it will make delay your riding if you do.

Depending on the brake make sure you check which size brake block you need for your brake model. Each brake model is designed slightly differently, selecting the correct block is critical for easy stress-free bleeds.

3. With your syringes prepped, brake caliper and hood ready, grab some paper towels and wrap both the lever and caliper close to where the bleed ports are to collect any excess fluid that will make its way out.

For all brakes with contact adjustments, rotate the barrel in the opposite direction to the arrow. For brakes with contact reach adjust, rotate the screw/knob until the lever tip is 75 - 80 mm away from the bar.

3. Once these two features have been set to the recommended service spec, then grab your T10 tool and unscrew the lever port, exposing the connection point where the syringe will go. Be sure that all the necessary rubber o-rings are on your connection points.

Wipe away any excess fluid that migrates to the lever body during this procedure.

4. Next move to the brake caliper on the fork or rear stay. Start by removing the port plug which is typically made of rubber. Once removed, use a 4mm hex key or wrench to loosen the bleed port valve with only a ¼ turn then gently retighten it.

5. Once this step is done, connect the additional syringe to the caliper body until you hear the distinct click noise. When connected, turn the nozzle of the syringe / bleed port connection no more than 1 full turn open. If you exceed 2, screw back in until the bleed port is closed.

6. With syringes connected, head to the lever and open the syringe clamp hose. From the top of the lever push the fluid within that syringe to the brake caliper syringe. Allowing the excess fluid within the system to migrate into the brake caliper syringe.

This is a great opportunity to check on the “health” or color of your fluid. If it has any discoloration, it is best to completely flush the system.

7. With new fluid in both syringes once the old has been flushed, starting at the bottom(Brake caliper), push the syringe while pulling gently on the top (Brake Lever) to allow fluid to travel between the two points.

You will want to push and pull fluid between the two points allowing for any bubbles within the system to travel out to the syringes. Repeat this process until the syringe hoses do not draw any air/ bubbles.

8. With all the air out of the brake hose system including the caliper and lever. Turn the Syringe at the brake caliper until it is closed completely. Then make sure to clamp your hose at the brake to prevent any further fluid from leaving the syringe body.

Now at the Lever with the syringe still connected and open, squeeze the lever and gently release. 9. With the syringe being held vertically, pull up on the plunger to create a vacuum or pressure where more air bubbles will migrate out of the system. Then press the plunger to pressurize the system. Repeat this process until only a small amount of bubbles travel out of the syringe hose.

Compress and Release the syringe once more, then close off the clamp at the hose. Remove the syringe from the brake lever.

10. Use a rag to remove any excess dot fluid that may escape from the port. With your T10 bit or wrench reinstall the bleed port screw into the lever being mindful to tighten just enough to allow the torque wrench to finish the job at 1.5 to 1.7 nM. The same will be done to the rear with a 4mm to be torqued down to 1.5 to 1.7nM.

11. Reinstall the brake caliper bleed port plug. Remove the bleed block. Reinstall your brake pads into the caliper and use the bolt to secure the pads. Be sure not to over-tighten this bolt—if it becomes seized, you might be S.O.L.

12. Lastly, reinstall your wheel, and chain. Rotate your wheel and double-check your work. Make sure all ports, bolts, and screws have been correctly reinstalled, and torqued to spec and that you have proper function of your brake.

Friendly reminder to dispose of your DOT fluid per the regulations in your area. Saving the environment is cool because you ride in it.

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