Brakes and rear axle: newbie questions- Mtbr.com
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  1. #1
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    Brakes and rear axle: newbie questions

    I did a search but couldn't find definitive answers here to two specific questions...

    I have a brand new bike and just built it up last night.

    1. The bike has Guide RS hydraulic brakes and thru-axles front and rear. I haven't had a chance to ride it yet (at all). I mounted and centered both brake calipers using the "loosen the mounting bolts, hold the lever, retighten bolts" process. The pads very slightly rubbed the rotors. I repeated the process and got the alignment even closer but it's still just scuffing the rotor. The scuff is not enough to slow the wheel noticeably but it is making a slight sound. Is this something that I just need to let "break in" through the bedding-in process? Should I take the wheel out and retract the brake pistons all the way manually?

    2. The bike has a 12mmx197mm rear thru-axle. The axle doesn't have a lever and is tightened using a 10mm Allen key. This is my first bike with thru-axles, is this type of thru-axle without a lever common? I assume this means I need to ride with a 10mm key, not a big deal but slightly annoying. Do people recommend I eventually swap the axle out for something with an integral lever?

    Thanks!

  2. #2
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    Calipers can be tough to line up, I do what you did but only slightly tighten then I eyeball em straight using a light under to help see. As far as axle, heck I would like one without the stupid levers. It's really up to you if you feel like it's to big of inconvenience or not.

  3. #3
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    Can't help with the thru-axle, other than wish I had one.

    For the brakes, keeping them straight when tightening down can be a challenge. I normally do the following:
    1. hold lever and tighten to take up loose slack
    2. release lever, hold lever and tighten each bolt quarter turn at a time till barely tight
    3. spin wheel to see if there is any rub
    4. if there is rub, loosen both bolts half turn, shake caliper, release lever, hold lever, and tighten half turn. go back to step 3.
    5. if there isn't any rub, tighten half turn on both bolts and check for rub again
    6. if rub, go to #4.
    7. If there isn't any rub, tighten both bolts another half turn, check for rub, then torque to spec.

    Tightening down the bolts can introduce twist to the caliper. It's a pain to do it over and over, but once set up right, it's worth the extra 5 minutes of annoyance.
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  4. #4
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    Problem with brake mounts like that is if you follow that "procedure" and look very closely at the caliper as you are tightening the bolts, you'll notice it "twists" when you start getting the bolts tight. This requires carefully increasing the torque on both bolts at once rather than just cranking one down and moving to the next. The other method I have to use sometimes is to manually push the caliper to one side while tightening the bolt, to keep it from twisting. You can try doing this with business cards in between the pads and rotors, but it wont solve the twisting problem that I've noticed over the years. This is why I liked non-post mounts, although they relied on facing of the tabs, they could be set up with shims to be perfectly centered, rather than post mounts, which can get pretty close, but sometimes not exactly perfect. There are other reasons post mount are used though, as you can't face the tabs on a carbon fork/frame, etc.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

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  5. #5
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    2. You should be carrying tools (small bike multitool) on your ride regardless.

  6. #6
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    yeah, doing the "squeeze the lever" method is generally never enough by itself. It's usually a good start, and then I have to tweak things. Sometimes with the business card method. Sometimes using a light and eyeballing it.

    And sometimes, the rotor needs to be trued.

    As for the thru axle not having a lever, I also would like my rear thru axle to be without a lever. On my bike, the lever sticks out and hits on stuff. It's annoying. But AFAIK, nobody makes a rear thru axle without protrusions like a lever that would fit my bike. Some companies make some wide enough, but the threads are wrong.

  7. #7
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    Quote Originally Posted by the-one1 View Post
    2. You should be carrying tools (small bike multitool) on your ride regardless.
    Agreed. As I said, no big deal. Still a long handled 10mm Allen key isn't tiny and not something you'll find on a multi tool.

  8. #8
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    Start with truing the rotors. They usually have some runout outta the package. The routine I use is using a feeler gauge between the pads and rotor. Works quickly and easily. One thing to note, when you do this, one piston will not retract as much as the other after a couple squeezes of the lever, repeat the procedure and you'll be good to go. Haven't had to readjust in a very long time.

    If you don't have the tools to true your rotors, visit an LBS that does, it makes all the difference...
    Get fAt, Stay fAt, Ride fAt
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  9. #9
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    ^Ditto.

    If you have intermittent rubbing, then your rotor is not running true. First thing to do before adjusting caller position is to check the rotor for wobbles. It takes a delicate hand to do the job efficiently, but if you have never done it before, go slow, with about the same pressure to pop bubble wrap.

    If you talk to your LBS and bring them some goodies, they would more than likely show you how to do it yourself.

  10. #10
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    Quote Originally Posted by abrar View Post
    ^Ditto.

    If you have intermittent rubbing, then your rotor is not running true. First thing to do before adjusting caller position is to check the rotor for wobbles. It takes a delicate hand to do the job efficiently, but if you have never done it before, go slow, with about the same pressure to pop bubble wrap.

    If you talk to your LBS and bring them some goodies, they would more than likely show you how to do it yourself.
    Beer is considered legal tender at most good bike shops!!! And usually is good for the receipt of preferential treatment. Weed can get you in even better...
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  11. #11
    Rippin da fAt
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    Runout in your rotor can prevent the brake from properly self adjusting and poor lever feel.

    Oh yeah! Fresh piping hot pizza can be helpful at the LBS as well...
    Get fAt, Stay fAt, Ride fAt
    Doctor recommended...

  12. #12
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    Are you a wrench at a shop somewhere, Banshee? We prefer morning coffee! Also, if you are going to bring beer and weed, make sure to come closer to closing hours. That way you can share it with your friendly neighbourhood LBS staff.

    Shooting the shit is part of the relationship!

  13. #13
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    Hell, they just might have their union break and safety meeting at a time when I'm not available, so gotta make sure they're stocked with the proper supplies!

    Besides, beer and cold pizza=breakfast.

    After hours = ride and test the Chris King power hitter mid ride!
    Get fAt, Stay fAt, Ride fAt
    Doctor recommended...

  14. #14
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    Yeah, I think I'll have a pro take a look at it if I can't get it right.

  15. #15
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    Took it to an LBS I know well. They charged me $45 to adjust the brakes. The pricing struck me as outrageous given that I needed no parts and it should be a ten minute fix for a good mechanic. However, I just wanted it fixed so I forked over the money. I picked up the bike three days later to find that they didn't fix a damned thing and that the brakes were clearly still rubbing. Gah. I complained, the LBS owner gave me a refund. No harm no foul.

    I took the bike home. After 20 minutes of watching YouTube videos, I took a crack at re-centering the calipers and a (very slight) truing of the rotors. Things I discovered:

    1. Holding the brake lever to get the caliper bolts started works well, but as you guys say the caliper starts to twist ever so slightly when you send the bolts home. I found that putting a light under the caliper to monitor the gap and using my hand to counter the torque as I finally tighten the bolts works. It took me three "grab brake lever, tighten slightly, spin wheel, tighten a bit more" etc cycles per caliper to get it just right.

    2. Truing new rotors if they just need a tiny amount of runout adjustment isn't difficult but it definitely requires a light touch. I used a paper towel to keep my filthy mitts off the rotors. Slight pressure is really all you need. This was one of those things you're sort of surprised works but it really does. Kind of satisfying, actually.

    3. For good measure, I took the wheels off, broke out my handy click-type torque wrench and made sure each rotor bolt had exactly the same torque. As I had hand tightened them before, I discovered that I was way off: basically every bolt needed a bit more torque. This of course caused the rotors to rub again, requiring me to start over. I really should do it right the first time.

    After about 45 minutes of work (and a large whisky sour), I got both brakes to run cleanly without rubbing. We'll see if my adjustment holds up.

    Overall, this was a bit of a twitchy adjustment for a newbie. I'm sure someone who does this daily can get brakes just right in their sleep...

  16. #16
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    Good on you but I usually lead off with the whiskey, the rest just kinda falls in place.

  17. #17
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    Quote Originally Posted by hiro11 View Post
    ... I used a paper towel to keep my filthy mitts off the rotors.
    For future reference, two cresent wreches with the jaws closed almost all the way work really well. Find the rotor bend, rotate that section of the wheel away from the caliper, give the rotor a light tweek.

    It's always good when someone learns to do this stuff themselves. Nice to know that you can now fix your brakes on the side of the trail, isn't it?
    "a hundred travel books isn't worth one real trip"

  18. #18
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    Kudos, hiro!

  19. #19
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    Sorry to revive this again.

    The rotors still aren't running true despite many sessions of delicately pushing and prodding the rotors in an attempt to get them exactly square. The tolerances are so ridiculously tight that it's tough to get this just right on your bike, I think you really need a truing stand with a rotor runout gauge to do this job properly if at all.

    In the meantime, I've requested that the bike seller provide me with new rotors as this is a brand new bike and I shouldn't have to deal with this. A new set of rotors is ~$75 from Amazon and I've ridden the bike exactly once. I'm a little frustrated...

    Two questions:
    1. Is this a common problem? Are brand new rotors frequently out of true enough that they need adjustment? Is this something that is a standard part of assembling a new bike these days? Am I just having bad luck here? I want to know how hard to push on the seller to fix the issue.

    2. What's the general consensus: is truing rotors worth attempting or is the standard advice to simply ditch them and buy new ones? Park's guidance on their own rotor adjustment site seems to be "you can try to true warped rotors but you should really just buy new ones". Several YouTube videos I've watched seem to corroborate this: don't even attempt truing, chuck the rotors and start over. I'm asking if I should try to take these to another shop or should I just give up and buy new rotors?

    Sorry for all of this, this is my first bike with disc brakes. I've built road bikes myself for twenty years and can assemble a road bike in about half an hour at this point, but disc brakes with very slightly warped rotors are seemingly much trickier than anything on a standard road bike.

  20. #20
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    It depends.

    I've seen some rotors out of the box that have been trashed before the first mile. But I've trued plenty of my own, too. Usually, I'm far less precise about it. I just grab the rotor with a clean rag and pull/push as needed. That only works for a slight wave. I've never had one that was badly warped. I've seen a couple that were so trashed from a wreck that the wheel wouldn't turn. Those were just replaced.

    If the noise is just annoying to you, it sounds like you just need thicker skin.

  21. #21
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    Since rotors are stamped out of sheet metal, there will always be some imperfections. I am talking about <1mm in deflection, either side. If you have a rotor that is moving >2mm in either direction, then it becomes a problem not worth fixing, maybe 40% of the time.

    Do not buy into the consumerist mentality. Everything is worth fixing, if not, at least attempting to fix.

    You will rarely have a perfect rotor, but what you could do is increase the tolerance by bleeding out a little fluid from the calliper. Depending on which brakes you have this could be really simple, or not worth the headache at all. The trick is to do it in such a way, that you do not let any air into the system.

    If you have the money for it, buy a new rotor. This is a normal enough problem, that if you push the LBS owner, you might get pegged for being an unreasonable customer.

  22. #22
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    Yeah, I'll readily admit that a major cause of this "problem" is garden variety owner neurosis.

  23. #23
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    I just checked back, and saw the mention of Guide RS brakes. Personally, I am not a fan of Avid/Sram hydraulics.

  24. #24
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    The companies that sell rotors recommend buying new rotors. shocking

    If they are truly warped through use, the metal is fatigued and would be hard to true. If they're new rotors, a new set of rotors will probably give you similar issues. You could contact the seller and try to get replacements or refund some money for shop work, but I wouldn't expect new rotors.

    Are the pads rubbing continuously or as the wheel turns. If it's continuous, it's caliper alignment. If it comes and goes as the wheel turns, it's a rotor issue.

    There is always the possibility that the rotor bolts aren't tightened down evenly. Easy fix with a t-25 wrench. You could also have bad brakes, but that'll take LBS support to resolve through warranty.
    "a hundred travel books isn't worth one real trip"

  25. #25
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    Quote Originally Posted by hiro11 View Post
    Sorry to revive this again.

    The rotors still aren't running true despite many sessions of delicately pushing and prodding the rotors in an attempt to get them exactly square. The tolerances are so ridiculously tight that it's tough to get this just right on your bike, I think you really need a truing stand with a rotor runout gauge to do this job properly if at all.

    In the meantime, I've requested that the bike seller provide me with new rotors as this is a brand new bike and I shouldn't have to deal with this. A new set of rotors is ~$75 from Amazon and I've ridden the bike exactly once. I'm a little frustrated...
    .
    Send me a PM with your address and I'll send you new rotors for free. I have 180mm and 160mm - all true.

  26. #26
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    Thats one way to solve a problem. Cheers, Scott!

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