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I recently bought a bleed kit (for shimano brakes from shimano) and used it on my hydraulic brakes (successfully as far as I can tell). During cleaning up I noticed the syringe says it was for single use only. This seemed annoying to me at first (produces waste, requires to actually get new ones - shop opening hours / struggle with shipping companies …) so I was wondering what the reasons might be and came up with the following candidates:

  • They come from the same production line as medical syringes, where they really really shouldn't be used more than once. So the label is on it by default and the production company never bothered to figure out what actually happens upon multiple uses.

  • The syringe won't be clean after the first usage and the oil damages the plastic over long exposure, so you get traces of whatever comes out of that reaction into the oil, and the syringe won't work properly (piston not tight / piston stuck)

  • The oil attracts dust and dirt, so after storage I would contaminate my brake with "bike tool drawer dust".

  • I might not remember if I used a syringe for mineral oil or dot 5.1 / dot 4 and run into danger of mixing the two when using on a different bike, and all just because I tried to safe a few bucks on a new syringe. (or even worse, who says I only use the syringe for brakes? I might mix all sorts of liquids)

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  • I use my syringes for years and with different fluids and the worst what happened was increased friction so you have to apply more force to the plunger. Am still interested in answers, so have an upvote. – Klaster_1 Aug 23 '18 at 8:52
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    They might be sourced from medical suppliers where this would be the norm. – Carel Aug 23 '18 at 9:33
  • Used mine multiple times over the years without issue – Andy P Aug 23 '18 at 10:33
  • Did you buy from Shimano, or from a third party to suit Shimano procedure? Might have a bearing on the answer. – Swifty Aug 23 '18 at 15:38
  • From Shimano, added. – pseyfert Aug 23 '18 at 15:43
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You can likely use it multiple times.

Obviously, you don't want to mix different fluids in that are incompatible; you could clean the syringe by drawing in and out a bunch of times, but its probably less convenient than just keeping a separate syringe for different fluids.

They may fail at some point (likely the gasket), but that's probably fine; just use a new syringe when it fails. This may occur between multiple uses if you don't clean/if the materials degrade the syringe over time. But its not a big deal.

Note that even humans have fairly high success rates reusing syringes, particularly drug addicts in first world countries and oral syringes for babies (which is closer to the type of syringe your bleed kit has). Though, obviously, for medical reasons, you don't always want to (usually don't) want to reuse a syringe.

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  • I'd stick each syringe in a plastic clipseal bag and clearly label it with the fluid type. – Criggie Aug 28 '18 at 8:29
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    I've been using the same syringe for bleeding Tektro and Shimano brakes for years without any problems whatsoever. – Mick Jan 22 at 9:38
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I know it’s an old question, but I just received my bleeding kit, and I was wondering the same thing. I looked up ‘syringe’ on Amazon, all of them have markings saying ‘discard after use’ or ‘single-use only’, regardless of their intended purpose, including some where the description clearly states that they’re reusable, like the ones meant for cleaning a baby’s nose with saline solution (just a plain syringe with a plastic attachment). Chinese factories that make them by the millions don't want to bother with custom versions, a single machine stamps all markings at once. This said, I would not switch between mineral and DOT fluid without thoroughly cleaning the syringe.

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  • Given the low price of the components, and the high cost of screwing up a brake system by even trace contamination, I'd suggest keeping completely separate kits for each kind of oil and never ever changing them. One could even have separate clean and dirty syringes for each oil and it still wouldn't break the bank. Good first answer - keep it up ! – Criggie Apr 15 at 5:29
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When done with the syringe DON'T add mineral oil and lube the rubber gasket with it. It's the oil that weakens/breaks down the rubber causing it to eventually fail.

If you want to reuse the syringe just make sure you clean it thoroughly. This will make it last longer but eventually it will need to be replaced. If you want something that will last it'll cost you more money. Just get the Park Tools brake kit which is designed to last and it's what the shops use as they use it over and over countless times a year.

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    I don't have direct experience with this, but this seems plausible. We do know that you have to design rubber seals inside brakes to work with either DOT or mineral oil, and if you believe Shimano or Magura the exact composition of the mineral oil also matters. So the seal's gasket could be the issue as you described. In your experience, would it help to clean the gasket off with alcohol as in Herr Derb's answer, or is that unnecessary? – Weiwen Ng Jan 21 at 20:20
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    @Weiwen Ng the Shimano/Magura thing is contestable. Many people use “shigura” brakes without issues with a Shimano lever and Magura caliper. – MaplePanda Apr 13 at 17:25
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Simply clean them with some cleaning alcohol spray. After it dried, lube it with a little bit of the hydraulic oil again (otherwise you would damage the rubber part of the piston) and you are ready to put them back to your tools an reuse them again.

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