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  1. #1
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    Question: How often do you bleed your brakes?

    I'm in my 3rd season on my MTB with Shimano Saint M820 hydraulic disc breaks. The rear break is not performing well, feels very soft, have to apply a lot of pressure and they squeal abnormally though I see no physical issues.

    I'm going to bleed the breaks figuring that is the problem because when I apply pressure I don't feel the pressure applied though the break line to disc. Without load the rear break does work and stop the tire from rotation. The front appears fine.

    My question is do I completely flush the system or simply top it off?
    How often are you to perform this type of maintenance?

    I ride 1 or 2 times a week for 1-2 hours each ride: 30% pavement, 70% deep woods.

  2. #2
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    All over the board for me.
    During bike park season when I'm riding lift assist 4-5 times times a week for 4 months, I'll often bleed Saints 1-2 times a month.
    For normal trail riding with several rides a week sometimes I can go months without having to bleed my XTs
    Depends on the brake and it's age and amount of miles in my experience.
    I've got a pair of Guides with almost daily riding for 6 months that do not yet need bled.
    I bleed Shimanos as soon as I notice lever pump up or variable pad contact points in the lever throw or excessive lever travel.
    A good bleed where all air is removed will perform and last longer than a mediocre bleed.
    Sounds like it is time for you to do the full bleed/flush, however a quick bleed + top off would likely improve performance as well.
    Also, since you are getting squeal, check caliper alignment and rotor + pad contamination as well.
    Also check overall pad life/thickness.

  3. #3
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    Doing a complete flush is so easy it's pointless not to. I don't do my Shimano brakes every year though, only when they need it and it can be years until they do. I have a pair that haven't been bled in three-years and are still fine.

  4. #4
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    I typically bleed my brakes every spring, even though the fluid is still in good condition, itís just part of getting my bikes ready for riding season. I also need to change my pads every year sometimes twice a year on my DH bike. I would recommend bleeding your brakes and checking you pads if you havenít already.

  5. #5
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    Quote Originally Posted by michealj View Post
    I typically bleed my brakes every spring, even though the fluid is still in good condition..
    That's like throwing out fresh bread because you were in the kitchen anyway. Except it costs more and takes longer.

  6. #6
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    Why-----I have never done this and my XT's are still good after several years-----I mean in my car they do not need this even after 10 years and 150K====are not these sealed systems?

  7. #7
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    Quote Originally Posted by pctloper View Post
    Why-----I have never done this and my XT's are still good after several years-----I mean in my car they do not need this even after 10 years and 150K====are not these sealed systems?
    Actually you should have replaced your brake fluid 2-3 times now. Called maintenance.

    Has nothing to do with "sealed system" has to do with heat generate and just age of fluid.

    Once every yr or 2 is pretty normal for mtb brakes. Good idea to do it depending on how hot you get them regularly.

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  8. #8
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    Once a year or so. My fluid definitely darkens/has some blackish fluid in when I do.

  9. #9
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    Quote Originally Posted by Mr Pig View Post
    That's like throwing out fresh bread because you were in the kitchen anyway. Except it costs more and takes longer.
    Bleeding the brakes does not require replacing the fluid, if the fluid is still in good condition, bleeding is simple removing any air that may be trapped in the system. Kind of like throwing out the heels of said bread. You should be replacing you fluid once the performance starts to degrade, as you pointed out. Mineral oil makes a better brake fluid because itís boiling stays about the same once itís wet, but will break down from heat cycling of hard use.

    Quote Originally Posted by pctloper View Post
    Why-----I have never done this and my XT's are still good after several years-----I mean in my car they do not need this even after 10 years and 150K====are not these sealed systems?
    Different systems, unless you are using mineral oil brake fluid in you car, you should be flushing your brake system every few years depending on climate and brake usage. Most brake fluids are hydroscopic and will absorb water through the walls of your brake lines, master cylinder/caps and other entry points, which over time significantly reduces the boiling point of the fluid, which significantly reduces the fluids ability to not be compressed.

  10. #10
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    I rarely do a complete flush, but I'll "top off/check for air" on my Shimano's on occasion....maybe once or twice a year.

  11. #11
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    Quote Originally Posted by michealj View Post
    Bleeding the brakes does not require replacing the fluid, if the fluid is still in good condition, bleeding is simple removing any air that may be trapped in the system. Kind of like throwing out the heels of said bread. You should be replacing you fluid once the performance starts to degrade, as you pointed out. Mineral oil makes a better brake fluid because itís boiling stays about the same once itís wet, but will break down from heat cycling of hard use.
    If you're going to bother with bleeding in the first place, you might as well fludhing the old fluid regardless of fluid type. If there's a build up of air in system, it is what it is at that point. If water gets into the system thru the seals, housing, etc it will drop the boiling point to that of water and it will pool in the system. Thus flush that crap out fast.

    That said, mineral oil is cheap so don't be a miser and flush it. Also stick with Shimano oil, and stay away from Magura which has terrible boiling points.

  12. #12
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    Probably about every 2-3 years here. Sooner if there's a problem or I'm changing part of the system. It depends on DOT fluid vs mineral oil too, as mineral oil is supposed to be hydrophobic (repels water) and not hydroscopic (absorbs it).

    Quote Originally Posted by michealj View Post
    Different systems, unless you are using mineral oil brake fluid in you car, you should be flushing your brake system every few years depending on climate and brake usage. Most brake fluids are hydroscopic and will absorb water through the walls of your brake lines, master cylinder/caps and other entry points, which over time significantly reduces the boiling point of the fluid, which significantly reduces the fluids ability to not be compressed.
    QFT. Water lowers the boiling point and generally isn't great for the components. Most car manuals say 2 years iirc.

    Either way, the best thing to do is read the instructions for your brakes and stick to what the manufacturer recommends. The engineers that design the product should unilaterally know better about what their product needs.
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  13. #13
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    When they start to feel mushy. A partial bleed with the funnel usually fixes that.

  14. #14
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    I've never had to bleed the brakes on my MTBs. That being said...

    Quote Originally Posted by ikolbyi View Post
    I'm in my 3rd season on my MTB with Shimano Saint M820 hydraulic disc breaks. The rear break is not performing well, feels very soft, have to apply a lot of pressure and they squeal abnormally though I see no physical issues.
    It sounds like you have contaminated pads. Make sure there are no signs of oil leaking from around the pistons, and if not then buy new pads and be careful to not get them contaminated.

  15. #15
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    Bled the XTs on my squishy for the first time ever a week ago. Had to flush the front one six or seven times before the fluid turned from opaque black/brown to transparent light red. The rear only needed two flushes.

    This was after two full seasons and about 3,000 miles ... so I would say, "More often than that."

  16. #16
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    Quote Originally Posted by pctloper View Post
    Why-----I have never done this and my XT's are still good after several years-----I mean in my car they do not need this even after 10 years and 150K====are not these sealed systems?
    It's actually more important to replace your automobile's brake fluid than your bicycles. Mineral oil isn't hygroscopic like DOT.

  17. #17
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    Quote Originally Posted by RAKC Ind View Post
    Actually you should have replaced your brake fluid 2-3 times now. Called maintenance.

    Has nothing to do with "sealed system" has to do with heat generate and just age of fluid.

    Once every yr or 2 is pretty normal for mtb brakes. Good idea to do it depending on how hot you get them regularly.
    Depends on the system, but usually I don't bother until symptoms appear. For SRAM, that falls in line pretty well with "every year or 2". For Shimano, it varies a LOT...anywhere from never to 3 times in a year when I had a leaky piston (replaced the caliper the 3rd time).

    Quote Originally Posted by Schulze View Post
    It's actually more important to replace your automobile's brake fluid than your bicycles. Mineral oil isn't hygroscopic like DOT.
    This. I don't bleed Shimano until they tell me they need it.

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