My SRAM Rival disc brake pistons
weren't returning well, and there was
a significant left-right difference in piston travel
when squeezing the brake lever,
so I removed the pistons and
loosened the connecting bolts on the left and right sides of the brake to disassemble it.
With the brake pads removed, if you
squeeze the brake lever repeatedly,
one piston will suddenly pop out on one side
and all the brake fluid will leak out at once.
For the other side, I pushed the red end of the
specialized tool shown in the image above into
the hole where the piston came out.
Then I inserted this black part,
and since the brake fluid had drained,
I attached a syringe filled with fluid to the brake side
and squeezed the brake lever repeatedly while applying pressure—
then the other piston also popped right out.
You can see holes in both parts in the image above, but
aligning them that way doesn't work with the slots—very confusing.
I don't think the red part needs a hole at all.
↑The seal attached inside the brake piston hole, and
spare piston parts are
available from SRAM.
This time I'm not replacing them yet.
From the state shown in the image above, the piston
won't go in even if I push hard with my thumb—
there's resistance.
There are scuff marks on the side of the piston.
Avid, the manufacturer of SRAM brakes,
makes something called DOT grease,
and applying this to the piston seal
makes the piston movement extremely smooth and light.
In the background of the image above, I've already pushed it in, but
I'm gently pushing this piston in
with just my pinky finger—it slides right in.
One piston wasn't returning properly,
and with new brake pads the adjustment had become
extremely finicky. Now that's fixed,
the spongy feeling in the brake lever is gone,
and that crisp click is back.
This is my first time doing this on my own bike,
but I've had customer disc brakes where
the lever pull felt squishy with some dead space
at the start of the stroke. When I overhauled the brake caliper side,
it improved dramatically. Poor piston return causes that
lever feel issue—it's not a lever problem.
Attach syringes to both the brake caliper and lever,
and after repeating the push-pull action several times,
DOT grease debris will start flowing
from the caliper side into the syringe.
After a certain point it stops completely,
so I believe I've recovered almost all the excess grease.
Oh, the title says "front" brake because
I only use the front brake.
I've never stopped the spinning rear wheel
with the brake caliper.
Yet somehow—whether from standing climbs causing rub
or sand getting caught while riding in the rain—
the rear rotor has faint scuff marks on it.
weren't returning well, and there was
a significant left-right difference in piston travel
when squeezing the brake lever,
so I removed the pistons and
loosened the connecting bolts on the left and right sides of the brake to disassemble it.
With the brake pads removed, if you
squeeze the brake lever repeatedly,
one piston will suddenly pop out on one side
and all the brake fluid will leak out at once.
For the other side, I pushed the red end of the
specialized tool shown in the image above into
the hole where the piston came out.
Then I inserted this black part,
and since the brake fluid had drained,
I attached a syringe filled with fluid to the brake side
and squeezed the brake lever repeatedly while applying pressure—
then the other piston also popped right out.
You can see holes in both parts in the image above, but
aligning them that way doesn't work with the slots—very confusing.
I don't think the red part needs a hole at all.
↑The seal attached inside the brake piston hole, and
spare piston parts are
available from SRAM.
This time I'm not replacing them yet.
From the state shown in the image above, the piston
won't go in even if I push hard with my thumb—
there's resistance.
There are scuff marks on the side of the piston.
Avid, the manufacturer of SRAM brakes,
makes something called DOT grease,
and applying this to the piston seal
makes the piston movement extremely smooth and light.
In the background of the image above, I've already pushed it in, but
I'm gently pushing this piston in
with just my pinky finger—it slides right in.
One piston wasn't returning properly,
and with new brake pads the adjustment had become
extremely finicky. Now that's fixed,
the spongy feeling in the brake lever is gone,
and that crisp click is back.
This is my first time doing this on my own bike,
but I've had customer disc brakes where
the lever pull felt squishy with some dead space
at the start of the stroke. When I overhauled the brake caliper side,
it improved dramatically. Poor piston return causes that
lever feel issue—it's not a lever problem.
Attach syringes to both the brake caliper and lever,
and after repeating the push-pull action several times,
DOT grease debris will start flowing
from the caliper side into the syringe.
After a certain point it stops completely,
so I believe I've recovered almost all the excess grease.
Oh, the title says "front" brake because
I only use the front brake.
I've never stopped the spinning rear wheel
with the brake caliper.
Yet somehow—whether from standing climbs causing rub
or sand getting caught while riding in the rain—
the rear rotor has faint scuff marks on it.