Brake piston pop out!

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  • #530385

      Recently I remove the brake pads from the 2 front disk brake of my Yamaha FZ1. My intention was to clean up the pistons and its surrounding areas. Having done so, I even press in the 4 pistons and then pump them out again by pressing the hand brake on the handle bar. Due to my carelessness, one of the pistons pop out of its housing and a lot of brake fluid came out. I then manage to push back the piston into its housing. I then bleed the brakes and so far the brakes are working well.

      There is no way for me to know whether the piston has gone into the housing properly, especially the rubber dust ring and the round rubber ring ( squarish cross section, so called ‘the little guy’ by Eric) Would appreciate if anyone can enlighten me on what I have done.

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    • #530539

        So the brakes are working right. When you look at the caliper and the pistons, do they all look flush and even? If so then I wouldn’t worry about it.


          Thank you Celtic comrade for your quick and kind reply. 🙂 The piston and caliper look flushed and level. So far the brakes are doing fine. I just hope everything turns out well. In fact after the cleaning session, the brakes are now more effective.

          Anyway, I also noticed that all the 4 pistons for each brake do not come out with similar distance. Some come out more, some less. Really don’t know whether this was done intentionally by Yamaha.

          When pushing the bike around, at the extreme turning end of the handle bar, there is a tendency for the brakes to give out a slight squeaking noise. This noise was evident before and after the cleaning session. I was wondering whether this was caused by the piston not having retracted sufficiently into the housing. Anyway I’ll monitor closely the brakes and let you guys know if there is any further problem. Meanwhile, get dirty guys, ride more and be happier.


            You’re fine. Motorcycle brake systems are more forgiving than cars. You can easily put back a brake piston without any effort and without it leaking. Just make sure you bleed them, as you have done so. As for if Yamaha designed them that way you ask, I’m not sure. The brake noise could be a number of things. My experience points to brake lube. You have to lube all contact points with brake grease.


              Like already stated, if it looks flush even and symetrical with the other side, it is okay. If the fluid seal wasn’t correctly located, I doubt you would have been able to force the piston back into the caliper.

              Yamaha designed each of the four pistons to exert roughly equal force on the brake pads. I say this because they are all the same size and sit in a bore of the same size. They are (in theory at least) all exposed to the same force from the brake fluid behind them because the fluid is free to flow to all four equally from the line to the calliper.

              What often happens, particularly with older bikes, is that the pistons only move a very small ammount in and out, so over time and even with the dust shields, they accumulate dirt and grit on the seal lips and between the piston and bore. Eventually, it may even corrode the surface of the pistons. Which will cause some to move more easily than others.

              Mostly you can tell by feel. If, when you pull the lever as hard as you can, the front wheel can’t be moved and the lever stops well before contacting the bar and doesn’t feel spongy, your brake hydraulics are working fine.

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