Replace the Shimano brake fluid

The hydraulic fluid is not eternal. It ages, heats, charges itself with water and denatures. Purge replaces part of it, but there is still a lot of dirty liquid left… Here’s how to start with a clean fluid!

Mechanical summary

The tools

To replace the Shimano brake fluid, you need a complete bleeding kit for Shimano brakes or a model that is compatible. It consists of a syringe with its fitting, a funnel, the funnel cap, but also a reducer that allows you to fix the funnel to the latest generations of brakes. Caution, it is sold separately at Shimano. You will also need a used oil collector and a blocker. We will add the Shimano oil in good quantities, if we want to preserve the warranty. You will then need a bubble level, allen wrenches for your stem (4 or 5 mm), a 2 or 2.5 mm allen wrench and a 7 mm flat wrench.

Pictures © Frédéric Iehl

Time and difficulty

If the operations are chained in the right order and without haste, we are on an average level of difficulty. So you will have to take your time. Count 30 minutes per caliper, including purge. In one hour your braking circuits will be operational! If you have very old oil, in your brakes, don’t forget the gloves and eye protection. New mineral oil is not harmful to the skin, but it remains mechanical oil, and when it is used… we might as well avoid contact. It will then have to be thrown in a garbage dump or recyclery plant. So we proceed as for a purge at the beginning and above all we finish as a purge!

Stage 1

Replace the Shimano brake fluid

We will loosen the stem to tilt the hanger and bring the lever into a good position.

Stage 2

The lever must be tilted to bring the bleeding hole horizontally, the highest point of the system. The top of the bubble level is aligned with it…

Replace the Shimano brake fluid

Stage 3

Replace the Shimano brake fluid

We tighten the stem to prevent it from moving during purge. We don’t rely on it, of course, but it’s better that everything fits. Especially the funnel…

Stage 4

At the top of the lever, under the cover, there is the purge screw.

Replace the Shimano brake fluid

Stage 5

Replace the Shimano brake fluid

We loosen the screw and avoid losing it or losing the O-ring…

Stage 6

The funnel adapter is screwed on the bleeding screw. Neither the lever nor the pistons are touched. We will have disassembled the pads before starting and put a blocker.

Replace the Shimano brake fluid

Stage 7

Replace the Shimano brake fluid

We then screw the funnel. We make sure that everything is blocked.

Stage 8

We fill the funnel to the maximum. Keep the can nearby…

Replace the Shimano brake fluid

Stage 9

Replace the Shimano brake fluid

At the bottom purge screw, the used oil receptacle (can or plastic bag) is connected.

Stage 10

We fix the hose lock.

Replace the Shimano brake fluid

Stage 11

Replace the Shimano brake fluid

And the bleeding screw is opened by a quarter turn. No more…

Stage 12

The cap is removed from the funnel.

Replace the Shimano brake fluid

Stage 13

Replace the Shimano brake fluid

The used fluid will flow. Complete the level in the funnel, the air must not enter the circuit… With a funnel and a half we should have « cleaned » the circuit. If the replaced oil is old, you will see the color change.

Stage 14

We fill the funnel by leaving oil in it…

Replace the Shimano brake fluid

Stage 15

Replace the Shimano brake fluid

And tighten the lower bleeding screw.

Stage 16

Disconnect the bleeding tube and wipe.

Replace the Shimano brake fluid

Stage 17

Replace the Shimano brake fluid

We arrange for the funnel to be half filled with fluid.

Stage 18

We connect the syringe, filled to the maximum, and block the hose. And we proceed with the purge (go directly to step 13).

Replace the Shimano brake fluid

Even if you have « flowed » the hydraulic oil properly, there may be air bubbles that remain or appear. So when you need to replace the Shimano brake fluid, don’t forget the purge! This does not add too much time and it will allow you to benefit from top braking!

Mechanical summary

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