How to Rebuild a Motorcycle Master Cylinder

This motorcycle master cylinder is from a 2003 Suzuki SV1000, we decided to rebuild it at the same time that we rebuilt the front brake calipers. The reason for this was excessive lever travel - the brake lever had almost " of movement before it applied pressure to the brakes. This wasn't due to air in the system - it was caused by sticking caliper seals that caused the pistons to retract slightly after braking, increasing the distance they had to move to make contact again. A motorcycle master cylinder rebuild is a pretty straightforward process. Here are some tips that make the job easier:
  • Get a service manual - this is where you will find all of the specifics for your ride
  • Wear gloves - brake fluid is bad for your skin
  • Get a good pair of snap ring pliers - the set we used were mediocre at best, this is the recommended pair: Motion Pro Master Cylinder Snap-Ring Pliers
  • Cleanliness is important - make sure you've got a clean space to work, introducing dust/dirt to the master cylinder can cause damage
This guide covers rebuilding the master cylinder - removal from the bike is usually simple and varies widely depending on the model. The SV1000 has the fluid reservoir integrated into the casting, but many sport bike master cylinders have a reservoir that is removable from the unit. Keep in mind that the number/type/size of components will vary by ride, this guide gives a general idea of how to rebuild a motorcycle master cylinder.
We used Suzuki OEM replacement parts for this project, all of the components shown here were included in 59600-45860.
Once the master cylinder has been emptied and removed from the bike, the first thing that needs to come off is the dust boot.
A new one was included in the kit so there was no need to worry about tearing it.
Pull the dust boot off of the end of the piston.
The wide end of the dust boot sits down against the snap ring that retains the piston, and the outer end of the dust boot is held in a groove on the end of the piston itself. On some master cylinders the dust boot will fit into a groove in the cylinder wall.
The snap ring is an internal type and a special set of pliers is required to remove it. On some master cylinders it may be harder to access than others - this one was fairly easy to get to.Note: The pliers we use here were flimsy and caused us some frustration, see our recommendation above for the ideal pair of pliers for this job.
The piston is being pushed against the snap ring by the return spring, so in order to remove the snap ring you'll need to put pressure on the end of the piston. We used a small socket extension to push down on the piston while using the pliers to compress the snap ring.
Once you?ve got a grip on the snap ring it should pull straight out.
When the snap ring is removed you can pull the piston out of the master cylinder - but it's more likely the return spring will make it pop right out when you let go of it.
The last parts to come out will be the return spring and the primary seal.
We used the handle of a small pick to poke the seal out of the master cylinder through the hole that the banjo bolt threads into.
The seal in this master cylinder sticks onto the end of the return spring, so they came out as a unit.
Here are all the parts laid out in the order they were removed, from right to left: dust boot, snap ring, piston with secondary seal, primary seal and return spring.
Clean the master cylinder inside and out. Our shop manual recommends that you use brake fluid for cleaning.
Once it is clean inspect the cylinder wall for damage - scratches, scuffing, wear marks etc. Some surface issues can be smoothed out by using an abrasive like emery paper. Keep in mind that any damage significant enough to cause your master cylinder to leak makes it worth replacing entirely.
Stick the primary seal onto the narrow end of the return spring, note that the concave side of the seal goes onto the spring, flat side towards the piston. Coat it in some brake fluid...
...and push it spring-first into the cylinder.
Make sure the piston and seal are coated in brake fluid first.
Insert the piston into the cylinder wide-end first.
It helps to load the snap ring onto the pliers and put it around the narrow end of the piston first.
While putting pressure on the piston (we used the extension again), squeeze the snap ring and slide it into the cylinder.
Push it to, or slightly past its groove then release the pliers. If it hasn't snapped into the groove you can move it around until it does by pulling outwards on the piston or pushing down onto the snap ring. If your master cylinder has a second groove for the dust boot you will need to make sure that the snap ring is seated in the second one - furthest into the cylinder.
After the snap ring is seated the last piece to install is the dust boot.
We stretched it onto the piston first...
...then pushed the wider end down against the snap ring.
That's it! You're ready to put the brake light switch back on, reattach it to your bike and bleed the air out of the system.
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