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  1. #1
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    New Pads...Bleed required?

    Guide brakes

    So I put some new pads in (first pad change from original setup on a new bike, so Iíve never cracked open the brake system for any reason).

    Getting wheels back on after pad change (due to pads being tight to get rotor in) was difficult but I got it in by using a plastic putty knife to spread them quickly get wheel on.

    Now the brakes are super tight, they are pretty much ďonĒ, as you can spin the wheel but feel the resistance.

    Pretty much figure I need to bleed. Just donít understand how if I never changed fluid level or opened the system, and am putting back to original spec pads etc, why suddenly it seems like thereís too much pressure and or fluid/air in the system.

    I donít have a bleed kit at the moment...is there a quick maybe temporary half assed way to relieve the system without needing to do a full bleed? Iím thinking maybe open the bleeder and let a little pressure off and hope things still feel and operate reasonably for now until i can deal with a full bleed service...?

    Thanks
    Mike


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  2. #2
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    you can crack the screw at the lever to let a little fluid out but in my experience if you just go ride them for a little bit the system will equalize pretty quick and everything will be fine.

  3. #3
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    Quote Originally Posted by dfinn View Post
    you can crack the screw at the lever to let a little fluid out but in my experience if you just go ride them for a little bit the system will equalize pretty quick and everything will be fine.
    Yeh I was considering the just go ride thing...when you say equalize...what does that mean exactly, like what physically is going to happen/change that will cause this equalization? If itís a closed system how will it work itself out?


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  4. #4
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    Is the caliper just not centered on the rotor with the new pads?

  5. #5
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    If the system was never opened / bled from when it was new, you shouldn't need to do anything other than push the pistons back in. I would spend a bit more time trying to get those pads pushed all the way back.

  6. #6
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    Quote Originally Posted by toast2266 View Post
    If the system was never opened / bled from when it was new, you shouldn't need to do anything other than push the pistons back in. I would spend a bit more time trying to get those pads pushed all the way back.
    Push the pads/pistons back? Why is this necessary? I got the wheels back on without pushing the pistons completely in...as soon as you pull the levers they will be maxed out again so whatís the purpose of pushing them all the way in?


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  7. #7
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    Quote Originally Posted by jamal View Post
    Is the caliper just not centered on the rotor with the new pads?
    No itís ok in that aspect


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  8. #8
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    Quote Originally Posted by ADKmike View Post
    Push the pads/pistons back? Why is this necessary? I got the wheels back on without pushing the pistons completely in...as soon as you pull the levers they will be maxed out again so what’s the purpose of pushing them all the way in?


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    There's a reservoir in the master cylinder at the lever. As pads wear, the pistons will migrate out to account for that wear, and there'll be less fluid in the reservoir because that fluid got pulled into the system to account for the pistons being further out.

    Now you've reset that process with new pads. So you need to push the pistons back in, which will push fluid back into the reservoir.

  9. #9
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    Not a guide user but I would try to make it work without bleeding, if you have never bled them it should work see if they will equalize

    i think in general its best to spread the pistons/ old padz in an old caliper that way you don't run the risk of fucking up the pistons and you don't care if you fuck the old padz up


    IME if you bleed with padz that are very worn you end up with too much fluid in the system and have to rebleed when you put new padz in
    Lee Lau - xxx-er is the laziest Asian canuck I know

  10. #10
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    to go along with what was said about the master cylinder and replacing the fluid also consider how the seal design works

    when pulling the brake lever the piston seal flexes which allows the brake to engage
    when you let go of the lever the seal retracts, but the piston itself isnt pulled back into the caliper with negative pressure, its just the flex from the seal not having back pressure on it anymore

    so over time as the pads wear the piston including the seal will migrate outwards to compensate for wear, and it wont retract until you press the pistons back into the caliper manually, which will also move the fluid back into the bladder in the reservoir and out of the caliper

  11. #11
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    Sure, your wheels went back in, but obviously they're too close, right? The pads can only retract so far on their own. How it works is the square shaped piston seal pulls them back just a touch to keep them from rubbing when you let off the brake. as the pads wear the pistons move out little by little to stay the right distance from the rotor and the reservoir in the lever handles the volume difference.


    Bleeding is done with a plastic bleed block in the caliper with pads removed. It would be unlikely someone bled the system with worn pads in it. Although if you have RSC levers the contact adjust needs to be all the way out and the reach in a certain spot. I think not doing that right could only result in too little fluid in the system, not too much.
    Last edited by jamal; 06-07-2021 at 10:05 PM.

  12. #12
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    Quote Originally Posted by toast2266 View Post
    There's a reservoir in the master cylinder at the lever. As pads wear, the pistons will migrate out to account for that wear, and there'll be less fluid in the reservoir because that fluid got pulled into the system to account for the pistons being further out.

    Now you've reset that process with new pads. So you need to push the pistons back in, which will push fluid back into the reservoir.
    This is the answer. Donít make it more complicated. Do this.

  13. #13
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    Quote Originally Posted by EWG View Post
    This is the answer. Donít make it more complicated. Do this.
    Ok thanks everyone for the responses. I didnít consider the fluid needing to go back into the reservoir by manually making it happen...it makes sense now that Iím reading the replies here. I guess I figured it backed off on its own from the pressure of the new thicker pads.

    I saved my old pads specifically for if I ever had to pry against the pistons as to not mar anything or tear a seal...so Iíll pop the old pads back in and use a screwdriver against them to push the pistons in.


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  14. #14
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    If youíve ridden your bike enough to wear out the pads, you should bleed your brakes.


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  15. #15
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    Quote Originally Posted by joetron View Post
    If you’ve ridden your bike enough to wear out the pads, you should bleed your brakes.


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    My reaction same.

    Sram uses dot fluid like your car. Hygroscopic. Not that it’s exposed to moist air, but it is sitting there for years.

    There’s a thread here about cheap bleed kits. I bought one of each type. cheap and easy to use. Do it.

    https://www.tetongravity.com/forums/...b-bleed-system
    ďLife has become immeasurably better since I have been forced to stop taking it seriously.Ē
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  16. #16
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    As others have said push the pistons back in and you'll be good. I usually push them all the way back in, put the new pads in, and then they "correct" to the right spot after a few modulations. I do not bleed every time I change pads since that can happen pretty quick in certain conditions. I usually just bleed when they get shitty
    Quote Originally Posted by other grskier View Post
    well, in the three years i've been skiing i bet i can ski most anything those 'pro's' i listed can, probably

  17. #17
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    Quote Originally Posted by ADKmike View Post
    Ok thanks everyone for the responses. I didn’t consider the fluid needing to go back into the reservoir by manually making it happen...it makes sense now that I’m reading the replies here. I guess I figured it backed off on its own from the pressure of the new thicker pads.

    I saved my old pads specifically for if I ever had to pry against the pistons as to not mar anything or tear a seal...so I’ll pop the old pads back in and use a screwdriver against them to push the pistons in.


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    I think this ^^ is a good idea and will probably work, you hear about people facking up the end of the piston while pushing in pistons and you definalty don't want that, I only bleed brakes that are spongy myself



    minor thread drift: there used to be a brand of hydraulic brake in that same era as the hayes mags that was a closed system, if they got really hot the brakes would eventualy stay locked on, this happened on a long continuous steep decent. The bike mechanic in the group said " well i could crack that bleeder to release some pressure but if I fuck it up you got no brakes in a must have brakes zone"

    buddy pushed it down hill a very long way
    Lee Lau - xxx-er is the laziest Asian canuck I know

  18. #18
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    Don't forget about Guide's sticky lever syndrome. I quickly found out which of my brakes hadn't been warrantied the other day when it got hot as fuck out.

    If you're still having a bit of drag after you've pushed the calipers all the way in, it could be this.

  19. #19
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    Quote Originally Posted by joetron View Post
    If youíve ridden your bike enough to wear out the pads, you should bleed your brakes.


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    Yeh I know I know...I procrastinated on getting a bleed kit and now Iím trying to get the bike rideable for this weekend...wonít be getting a kit in time for that...but itís on my to do list along with a fork service.




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  20. #20
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    Quote Originally Posted by ADKmike View Post
    I saved my old pads specifically for if I ever had to pry against the pistons as to not mar anything or tear a seal...so I’ll pop the old pads back in and use a screwdriver against them to push the pistons in.


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    Even with the old pads in you will still likely have a hard time. I use a soft tire lever, like one of the bright blue plastic Park Tools one, and just gently press directly on the piston, with the pads out. This might not be the 100% correct way of doing it but I've changed probably 50 pairs of pads across my bikes over the years and never damaged a piston doing this.

  21. #21
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    good artical on alternatives to shimano brake padz
    also bedding in procedures

    https://nsmb.com/articles/alternativ...no-brake-pads/

    https://nsmb.com/articles/oem-altern...e-month-later/
    Lee Lau - xxx-er is the laziest Asian canuck I know

  22. #22
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    So I got the front working fine - def was just needing pistons pushed in. Still having trouble in the rear. One side piston is all the way in and the other side (inbound) itís pretty far out. Pushed on it pretty hard using old pads as a buffer. Bike is rideable but thereís def some resistance on the rear. Prob will polish my inbound pad.

    Is the issue with the Guide brakes related to a piston being stuck outward? And having ďunevenĒ piston protrusion (is normal ďequalĒ?)


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  23. #23
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    Quote Originally Posted by ADKmike View Post
    So I got the front working fine - def was just needing pistons pushed in. Still having trouble in the rear. One side piston is all the way in and the other side (inbound) it’s pretty far out. Pushed on it pretty hard using old pads as a buffer. Bike is rideable but there’s def some resistance on the rear. Prob will polish my inbound pad.

    Is the issue with the Guide brakes related to a piston being stuck outward? And having “uneven” piston protrusion (is normal “equal”?)


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    The Guide issue is at the master cylinder.

    I'd bet the piston is just slightly canted in there, which can make it bind up and tough to push back in. I'd try (carefully) pushing on the piston directly. A stout tire lever works well, or a box wrench can work well too.

    And when you're pushing the pistons in, you're fighting that fluid. The easiest way to get the pistons back in is to crack open the bleed port, push the pistons back in, and then re-bleed (the line would still have fluid in it, and the brake would probably still work, but the reservoir would need to be re-filled with fluid). But that obviously requires having a bleed kit.

  24. #24
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    so yer car or truck has hydralic brakes, do you bleed them every time you replace brake padz or just push the padz in and replace ?
    Lee Lau - xxx-er is the laziest Asian canuck I know

  25. #25
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    New Pads...Bleed required?

    Quote Originally Posted by XXX-er View Post
    so yer car or truck has hydralic brakes, do you bleed them every time you replace brake padz or just push the padz in and replace ?
    It is recommended to in most owner's manuals, but mostly just to circulate fresh fluid into the system. If you've topped off your brake fluid during the life of your pads your system could be overfilled though.

    I typically don't bother as it's dry as fuck here, my brake fluid still looks great in both of our rigs. I've done flush/bleeds on older vehicles I've bought though.

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