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With a bike featuring Shimano 486 Hydraulic Disc brakes and levers, what should I do if I wanted to maintenance them? I have no experience of brakes other than V-brakes so where do I begin? The front brake seem to work but the lever goes all the way down, the back brake doesn't work at all. The lever goes all the way down but the brake doesn't bite.

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    This seems like a very broad question -- it's basically, "Disc brake maintenance -- tell me all about it!" There are lots of good videos on Youtube (e.g., on the Park Tools channel and GCN) that go over the basics. I suggest you watch some of those so that you can ask a question that's more specific. – David Richerby Nov 14 '18 at 18:32
  • From your description it sounds like your brakes' hydraulic lines need bleeding to get rid of the air that got into them. But it might be something else: problems with the pads, leaky hoses etc. I agree with David that you should first look for general tutorials on hydraulic brakes service, then try doing it on your system, and if something is still not clear, get back with a more specific question. Good luck! – Grigory Rechistov Nov 14 '18 at 20:37
  • Has the brake ever worked, to your knowledge? – Criggie Nov 15 '18 at 6:02
  • Try bleeding the brakes, but if that seems to fix them but soon after the problem comes back then it's likely to be the seals and Shimano don't sell the parts. You can try changing the o ring seals as these can be obtained ymmv. I've found that if a bleed doesn't fix them then its time for new brakes. – Jackson Nov 15 '18 at 14:05
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Hydraulic disc brakes pads are self adjusting for wear, so if the lever needs to be pulled back too far, or is hitting the handlebar the hydraulic system needs to be put through the proper bleeding process to remove air bubbles. You also need to check for leaks and loss of fluid, and check the wear on the brake pads.

Hydraulic fluid cannot be compressed, but air obviously can. When you pull the lever the air bubbles are compressing rather than the pistons and pads being forced towards the rotor. It's kind of like having a spring in the cable of a mechanical V-brake system.

If you are unfamiliar with hydraulic brakes, you may find it better to have a good bike repair shop do the bleed process - it requires a special kit, replacement fluid and has to be carried out following proper procedure. If you want to learn how to do it yourself there are video tutorials available online (here's one) but you really need to check the Shimano manual to make sure you are following the correct procedure.

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