QUARANTINE
Rebuilding Master Cylinder
I try my best to be a responsible motorcycle owner but, like owning any vehicle, it can be a lot of work! And sometimes you just ignore the check engine light for as long as you can…
So several years ago my bike failed tech at a Thunderhill track day because the master cylinder was cracked. We ended up safety wiring the master cyclinder on, and I continued on my merry way like that for the track day and onwards to a few months ago. My brother had a few extras lying around and I ended up using one of those, I think one for a ZX10.
To back up for a second, the MC is the doohicky that takes force from your brake lever pulling in, pushes brake fluid down your brake lines, which ends up clamping your brake pads down on your wheel, allowing you to slow down and stop. I did a cursory Google search and found this article if you’re interested in reading more. Suffice to say that this system is crucial to safe riding. You know that something is wrong with your brake system if your brake lever starts to feel “squishy”, as in you have to pull very hard to get it to brake.
The reason I was rebuilding this MC is because my brother had acquired this master cylinder from Ebay and it’s generally good practice to clean out and replace the innards of these parts since you can’t be totally sure what shape the parts are in.
All I ended up needing to do was remove the lever from the MC, which is just one nut on the bottom and bolt with a flathead on top. The old bits and bobs actually looked okay.
This is very simple stuff where you just put the parts back together the way you took them out but if you’re bad at 3D visualization like I am, and also have a bad memory, I have two ways you can refresh yourself. First, I made a Youtube video. There’s also this photo which might help?
The hardest part of this will be the clip that holds the piston into the MC. It’s the flat, horse shoe shaped doohicky with two holes in the ends. You will need a pair snap ring pliers if you want to get this done in any kind of efficient way. My brother happens to have really nice ones, so this was a snap for me, so to speak. You will push the piston into the MC hole, then squeeze the ring with the pliers, then push the ring in until it snaps into a groove. As long as the ring is in the hole, you can stop using the pliers. You do want it to be fully snapped in, so you can push it further with a flathead screwdriver from there.
The arrows here are pointing toward the holes in the ring. I don’t think mine is actually pushed all the way in in that photo. You want enough room for the dust cover with the ball and push rod to have room to sit comfortably there.
The dust cover pops right in, so from there I just reattached my lever and voila :)
OH and last step, since I messed with the fluid system, I ended up having to bleed my master cylinder. There’s a bleed nipple on the MC for this purpose.
Finally, make sure to clean up all brake fluid off any surface it touched. It’s incredibly bad for paint, and for skin, and well. Probably everything. I was spraying my bike off with windex for some reason (suggestion from an AFM racer at least…)