Results 1 to 11 of 11
  1. #1
    mtbr member
    Reputation:
    Join Date
    Jul 2013
    Posts
    5

    Shimano SLX M666 Mystery. Please help.

    Hey guys,

    Decided to buy a set of used SLX M666 brakes for a new build. Reviews were solid. The brakes arrive. To test them out, I remove my Code 5's from my FS bike, put the M666 on and align them. No rub, even spaces between pads and rotor. As soon as I squeeze either of the brakes, there is a loud harmonic vibration. I feel it in both of the levers. I resurface the pads, clean rotors with alcohol. No difference. Front AND Rear both produce horrible noise. Put my Code 5's back on, no issues. I don't think its my disks.

    I buy new pads and new rotors anyway. Assemble and align everything on ANOTHER frame. A hardtail frame. I'm trying to rule all variables out here. New pads, new rotors, different wheelset, and different frame. Same harmonic vibration on both front and back brakes.

    I tell the seller this is BS and get a refund.

    Proceed to order another set of used SLX M666 from a different seller. They arrive. SAME F-ICKING thing.

    What am I missing?

    I also own a set of AVID Code 5's, a set of old Juicy 7's and a set of very old Hayes 9's. If there is contamination (wet, residue on rotor, etc) they all make a little noise/squeak. I wipe the rotor with my glove, and the problem is gone.

    Here I have brand new rotors, brand new pads, and two sets of brakes that sound like a horn when I touch them.

    I'm sorry for the long post. I want to understand...

    Edit: Lever feel is solid, they are not mushy at all. I don't think there is air in the system.

  2. #2
    mtbr member
    Reputation:
    Join Date
    Jan 2004
    Posts
    6,929
    How long have you spent riding the bike w/ the SLX's? I have put new pads on bikes and had little power & noise problems that disappeared after the brake pads bed in (sometimes miles).

  3. #3
    mtbr member
    Reputation: jfrbikes's Avatar
    Join Date
    May 2011
    Posts
    55

    Re: Shimano SLX M666 Mystery. Please help.

    To me sounds like they have not been bedded at all. In the stand most brand new brakes feel like ****.

  4. #4
    rebmem rbtm
    Reputation:
    Join Date
    Apr 2007
    Posts
    2,958
    Post a photo of the brake setup.

  5. #5
    mtbr member
    Reputation: honns's Avatar
    Join Date
    Sep 2011
    Posts
    520
    Have you bedded the pads and rotors at all?

  6. #6
    mtbr member
    Reputation:
    Join Date
    Jul 2013
    Posts
    5
    No bedding has been done. I cannot bring myself to leave the house and ride with these. I am a bit sceptical about bedding as being the cause of the vibration because I've never had to "bed" another brake set before. I know to avoid bombing down on a fresh set until some pad material is on the rotor, so as not to glaze the pads. But if I can throw literally throw any other one of my sets on with no issues, I tend to think its not a bedding issue. I can throw the Juicy 7 on either of the 3 wheelsets, same with the Code 5. Even the 10yo Hayes. No bedding, no noises or vibration.

    I thought maybe its sticky pistons. Does anything permanent happen to mineral oil when exposed to low temps (like those in the cargo compartment of an airplane)? Wouldn't more people have the issue then?

    If you guys say it's bedding, then the brand new set of Hayes Prime Comp that's coming as a replacement today should theoretically honk as well until I bed it? My Code 5's were purchased new and I never "bedded" them. They never honked like this. Will report back.

  7. #7
    mtbr member
    Reputation:
    Join Date
    Oct 2010
    Posts
    363
    You should always bed new pads/rotors. I generally do 10-12 hard stops at home in the grass or gravel to avoid flat-spotting the tires on concrete. Last thing you want is a new set of brakes failing you on the trail because they weren't properly set up!

  8. #8
    mtbr member
    Reputation:
    Join Date
    Nov 2012
    Posts
    23
    Not sure on SLX, but the XT's I have are shoking until bedded. I don't notice any vibration, but they squeal like anything untill they get a real good heat cycle into them (sometimes happens after a bike clean but not as bad as new), and they wear into the rotors (happens again if you put another set of rotors in, or have a secod wheel set you swap to on occassion).

    You need to bed brakes in properly. You mightn't have in the past, and it might have worked, but, going on experience in other sports, if you don't do a proper bed in, they don't work as well as they could until you fully clean them down and bed them in again (involving a rather caustic brake cleaner solution, and sanding of hte pads, as parts of the pads will have become glazed). I've seen similar things on the MTB, though not as pronounced.

    get them up to a decent speed (while riding, can't do it on the stand, as you need the weight on them) and hard on the brakes, coming to an almost complete stop, repeat about 10 to 20 times and they've usually stopped by then (or at least a lot better, and stop sortly into the first ride after that), and braking a hell of a lot better!.

  9. #9
    mtbr member
    Reputation:
    Join Date
    Jul 2013
    Posts
    5
    Thank you all very, very much for your replies. I think I may have miscommunicated myself a bit. English is not my first language. I know that before I can do any kind of hard riding with a new set of brakes, I first have to break them in. I think the proper term is "bed" them. I do that on any new brake I buy, as per manufacturer recommendations. I just don't think that is what is behind the honking/vibration.

    The thing is, prior to my experience with the m666, I haven't yet had a set of brakes, let alone 2 sets of brakes, honk and vibrate like this. I thought the issue was something other than bedding, because I've switched all of my sets back and forth between frames and wheelsets, and never had any noise like this. Prior to any kind of "bedding". The "bedding" then happened when I rode to the trail. 20-30 hard brakes on a flat surface, letting the pads cool in-between.

    I put on a new set of Hayes Prime Comps I ordered as a replacement and they didn't honk either. A slight squeal up front (there was something on the rotor, cleaned it with alcohol), but that's it. I followed the proper brake in as recommended by Hayes. They feel great.

    I still feel like I didn't get to the bottom of this. Did I just buy two sets that coincidentally both had sticky pistons? I don't want to invest more money into rebuilding a set I can return, but the question still bothers me.

  10. #10
    mtbr member
    Reputation:
    Join Date
    Jan 2004
    Posts
    6,929
    If they were my brakes I wouldn't have any problem running the bike around the block a couple times to see if the noise subsided - i wouldn't be afraid they were going to explode. Our shop has seen quite a few howling & vibrating brake sets. Pad contamination , hard compound & mis aligned calipers can be the cause of noise. I have seen rotors w/ high spots cause vibration. Sticky pistons usually made for constant rubbing sounds (no brake application).

  11. #11
    mtbr member
    Reputation:
    Join Date
    Jul 2011
    Posts
    346
    Different brakes act differently, so don't assume that because it doesn't happen with one set doesn't mean it won't happen with another.

    If I were you, I'd give the rotors a good cleaning with isopropyl alcohol (+90%), perhaps even a light rubbing with steel wool (make sure you get off any steel wool bits). I'd also clean the pads with alcohol. Make sure not to get hand oil on the rotors/pads.

    Then I'd do some good stops to bed in the pads.

    If you're still having noise, report back.

Similar Threads

  1. Another Shimano SLX M666 (2012) Review
    By jsilva in forum Brake Time
    Replies: 21
    Last Post: 07-18-2014, 08:40 AM
  2. Replies: 11
    Last Post: 06-03-2013, 09:08 AM
  3. Shimano SLX M666 honk?
    By jsilva in forum Brake Time
    Replies: 0
    Last Post: 05-08-2013, 07:05 AM
  4. Replies: 4
    Last Post: 07-26-2012, 02:05 PM
  5. Shimano SLX M666 or M665?
    By TacoBeer in forum Brake Time
    Replies: 5
    Last Post: 07-25-2012, 12:10 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •