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  1. #1
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    Hydrolic Disc Brake Piston offset?

    Hi MTBR.
    I am a noobie with Hydrolic disc brakes, and i dont know how to explain this very well, but i saw that the pistons on the hydrolic disc brakes are offset, and are already pushed out, even with no brake applied

    are the pistons supposed to be like this? or are they supposed to go back into the piston hole all the way?

    thanks
    Matt

  2. #2
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    It depends on how much they are sticking out. They should be more or less flush with the caliper so you probably have a problem. What kind of brakes are they? It sounds to me like you have an issue with sticky pistons. It's an easy fix though assuming that's the problem. Pull your wheel, take your pads out, and clean up the pistons really well with rubbing alcohol. Lubricate the clean pistons with brake fluid, wipe off the excess so you don't contaminate your pads upon installation, install them, put your wheel back on and you're good to go. A bleed may not hurt either but that may be better for a shop to do.
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  3. #3
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    most hydrolics self adjust so as long as there is no brake rub offset is fine. Be careful not to activate the lever with a wheel removed or you will have to pry the pads apart.

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    Quote Originally Posted by faceplant72 View Post
    Be careful not to activate the lever with a wheel removed or you will have to pry the pads apart.
    If you pull the lever with the pads out, you could lose your pistons and then all of the fluid so as mentioned, don't pull your lever without a rotor in place and especially not without pads.
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  5. #5
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    Quote Originally Posted by mtbnozpikr View Post
    It depends on how much they are sticking out. They should be more or less flush with the caliper so you probably have a problem. What kind of brakes are they? It sounds to me like you have an issue with sticky pistons. It's an easy fix though assuming that's the problem. Pull your wheel, take your pads out, and clean up the pistons really well with rubbing alcohol. Lubricate the clean pistons with brake fluid, wipe off the excess so you don't contaminate your pads upon installation, install them, put your wheel back on and you're good to go. A bleed may not hurt either but that may be better for a shop to do.
    They are sticking out about 3-4mm give or take. so i do believe i have an issue.

    I have the Shimano Deore LX hydrolic brakes.

    How would i clean the piston? would i pull them out completely? Ah, ive done a few bleeds before, so im fine, but this is the first time i really did notice the pistons sticking out so much. so i got alittle freaked out.

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    In the event that i do accidently pull the lever, while pads and disc are out, what should i do, if the piston does fall out?

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    Alright, it is easier to clean them than to bleed them. If you have cotton balls or q tips and rubbing alcohol you should be good. Just wipe them off really well and since they're sticking out you'll be able to get the sides of them as well. I asked you what kind they were so I could determine what type of fluid you're running. Mineral oil is what you need to lubricate them with as you probably already know. I just didn't want you to put DOT fluid on a mineral oil brake (you'll be in the market for new brakes a lot sooner than you thought).

    You shouldn't accidentally pull the lever. It should not be an issue at all, just don't do it. Assuming you already did and the piston already fell out, you've got a bigger issue. To be honest with you I've never had the problem because I have never pulled a lever with no pads in. I think; however, that you can push your pistons back in and then do a bleed assuming you didn't tear your seals. I'm not positive though. Again, it shouldn't be an issue if it's not already.
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    Awesome, thanks! Hopefully this is the problem. if not, i will report back.

    Alright, don't worry, i havent, its just once, my shirt caught onto the lever, while doing a bleed and i was glad i had a spacer in the brake.. i was wondering just in case

  9. #9
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    Quote Originally Posted by Mattlikestobike View Post
    Awesome, thanks! Hopefully this is the problem. if not, i will report back.

    Alright, don't worry, i havent, its just once, my shirt caught onto the lever, while doing a bleed and i was glad i had a spacer in the brake.. i was wondering just in case
    Great, good luck.
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    You probably don't have a problem. Hydraulic brakes self adjust for wear so that you don't have to pump up your brake lever in order to stop when your pads get worn out. Your car brakes work on a similar system, self adjusting for wear.

    As long as the pistons are coming out of the caliper roughly the same amount you are good to go. If you ever get worried, take a CLEAN tire lever and gently and evenly pry the pistons back into the caliper body and pump the lever back up. Always a good idea to clean the pistons before you press them back in.
    Don't you hate it when a sentence doesn't end the way you think it octopus?

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    Quote Originally Posted by Mattlikestobike View Post
    Hi MTBR.
    I am a noobie with Hydrolic disc brakes, and i dont know how to explain this very well, but i saw that the pistons on the hydrolic disc brakes are offset, and are already pushed out, even with no brake applied

    are the pistons supposed to be like this? or are they supposed to go back into the piston hole all the way?

    thanks
    Matt
    The pistons self-adjust for pad wear. The thinner the brake pads get, the farther out the pistons stay. They only retract a small, set amount to keep the gap between the pads and rotor consistent. If the pads are thin, the pistons will stay partially extended out of the caliper. Otherwise, the free lever travel would increase as the pads wear.

    You will have to push the pistons all the way back into the calipers when you install new pads to gain the necessary clearance.

    If your brakes are working OK and not rubbing the rotor, they are fine.

    Edit...beat again due to slow typing skills.

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    Quote Originally Posted by gmcttr View Post

    Edit...beat again due to slow typing skills.
    Typing classes in high school pay off again!

    Don't you hate it when a sentence doesn't end the way you think it octopus?

  13. #13
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    Quote Originally Posted by zebrahum View Post
    You probably don't have a problem. Hydraulic brakes self adjust for wear so that you don't have to pump up your brake lever in order to stop when your pads get worn out. Your car brakes work on a similar system, self adjusting for wear.

    As long as the pistons are coming out of the caliper roughly the same amount you are good to go. If you ever get worried, take a CLEAN tire lever and gently and evenly pry the pistons back into the caliper body and pump the lever back up. Always a good idea to clean the pistons before you press them back in.
    That's a good point with regard to the self adjusting pistons. It definitely depends on how your pads are as well.
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  14. #14
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    Oh, glad i havent touched my bike yet then.. Since my pads have about 5-10 mm on them left and need changing soon.

    How much spacing should there be inbetween 1 pad, and 1 side of the rotor? i have give or take 1-3mm

  15. #15
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    Quote Originally Posted by Mattlikestobike View Post
    How much spacing should there be inbetween 1 pad, and 1 side of the rotor? i have give or take 1-3mm
    If you've got 1-3mm you're golden. As people mentioned, if your pads aren't contacting your rotors, you're good. Assuming 1-3mm, that's plenty of space.
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  16. #16
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    awesome, thanks!

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