Published on May 4th, 2016 | by Greg O'Keeffe
Ask a Mechanic | Servicing SRAM Hydraulic Road Disc Brakes
Ken wants to know: What do you do to dial in SRAM road hydraulic disc brakes? Do you have any tips or tricks to share?
Getting the most out of your SRAM HydroR brakes is easy if you follow a few basic rules.
First off, always use a torque wrench.
This is important not just for the caliper mounting bolts (5-7 N∙m torque spec for post mount and 4.8-5.2 N∙m for flat mount), but also for the compression nut (5-6 N∙m torque spec) where the hose attaches to the caliper. It is especially important to use a torque wrench where the hose attaches to the lever assembly, as this attachment can be easily stripped if torqued beyond the recommended torque value of 3.9 to 4.4 newton meters
Second, follow the bleed procedure.
Not following the bleed procedure can damage primary seals in the lever, which can lead to leaks or brake failure. A common problem caused by not following the bleed procedure is an overfilled master cylinder reservoir. This removes any negative space in the reservoir leaving no room for the brake fluid to expand when it gets hot. Then when the brake gets hot, the expanding fluid will cause the caliper pistons to clamp down on the rotor and make your brakes drag or even lockup. Overfilled master cylinder reservoirs can also leak brake fluid, damaging seals in the lever assembly and damaging the finish of the lever when the brake fluid leaks out.
Third, service your caliper pistons
Over time caliper pistons can get sticky and no longer advance properly. This can lead to low braking power, a spongy lever feel, uneven pad wear, and noise.
Fixing the problem is often as easy as performing a piston advance. This can be accomplished by first removing the wheel and taking the brake pads out of the caliper; then using a plastic tire lever, push one piston in while you squeeze the brake lever. This will force the other piston to advance. After the piston advances, use the tire lever to press the piston back into the caliper to its original position. Repeat the process on the other side. Do this to both pistons three to four times and the pistons will free up and advance properly. Just be careful not to advance the piston so far that it falls out of the caliper.
Even if your brakes don’t have a piston advance problem, performing this procedure every time you replace your brake pads is a good preventative maintenance practice.
Fourth: Only use SRAM replacement parts.
Like many other high-end parts on modern bikes, SRAM HRD brakes are made to perform using only original equipment replacement parts. Don’t ever use mineral oil or DOT 5 brake fluid in a SRAM brake. They will destroy the brake’s seals, eventually causing brake failure and requiring replacement of the entire brake. Although DOT 3 and DOT 4 brake fluid are compatible with SRAM brakes, the brakes are designed around the highest performing DOT brake fluid available, DOT 5.1. This brake fluid has a higher boiling point than DOT 3 or DOT 4 for the best high heat performance.
Fifth: Select the right brake pad for your riding conditions
SRAM HRD brakes come stock with steel-backed organic brake pads. These are the best option for most road riding conditions and offer the best balance of power and control. SRAM also makes longer wearing steel-backed sintered metallic brake pads for extremely muddy conditions, typically encountered in cyclocross racing.
When selecting brake pads, be sure to use a dedicated set of brake rotors for each type of brake pad compound. So if you make the switch from one type of pad material to another, your brake rotors need to be swapped as well.
Sixth: Know when to replace your brake pads and rotors
Inspect your brake pads regularly to ensure that the overall thickness of the individual brake pads measures at least 2.5mm thick including the pad’s backing plate. When a rotor measures less than 1.55mm thick it needs to be replaced.
Lastly: Dial in your fit with reach adjust.
Get more power and control from by adjusting brake levers to fit your hands. The adjustment is located between the shift lever blade and the brake lever blade on the underside of the brake lever. Just pull back the shift lever to access the 2.5mm Allen reach adjustment screw.