Forum home Mountain biking forum MTB workshop & tech

Avid Juicy 7 problems - too much stroke for pad contact

strakstrak Posts: 439
edited February 2008 in MTB workshop & tech
Hi,
Have had this problem on the back brake since new.
Ive adjusted the pad contact adjuster fully out, and the lever still comes too close to the bar before pads contact disc.

Im not sure what the issue here is - Has it not been properly bled?

Have lloked at the SRAM guide, is it possible to try and bleed without the kit? I notice the bleed ports have special inserts required, so doesnt look like the old hose over the mipple technique can work??

puzzled :(

Posts

  • nicklousenicklouse Posts: 81,520 Lives Here
    have you adjusted the lever adjuster? that does the reach and stroke. then play with the pad adjuster.

    How old are the brakes?
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • strakstrak Posts: 439
    08 Juicy 7.
    THe lever adjust is as far out as I would like it, thats the problem.

    Then with the pad adjust fully out, it still comes in too close to the bars.
    I also notice the pad contact moves after bikes been left vertical or upside down. Is this normal or indicative of air in the system?
    cheers
  • nicklousenicklouse Posts: 81,520 Lives Here
    so how long have you had the brakes?

    new fit or.....
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • strakstrak Posts: 439
    newly fitted boss
  • nicklousenicklouse Posts: 81,520 Lives Here
    so the pistons will not have settled yet. pump the lever and them hold wish a zip tie over night.

    this is presuming that the caliper is correctly fitted and aligned.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • strakstrak Posts: 439
    done that already, then centralised the caliper with the brake on.

    Its like the lever has to travel further to move the calipers the same distance than on my front brake? strange
  • nicklousenicklouse Posts: 81,520 Lives Here
    have you left them ON over night?
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • dave_sdave_s Posts: 4,362
    It did that on the Juicy Sevens I fitted but I took up the play with the lever reach adjuster (small allen key inside the lever near the lever pivot) and got the reach and bite point spot on.

    Otherwise take them to your LBS to adjust and bleed the brakes.
    Dave S
  • skylinerskyliner Posts: 613
    The mushy lever when the bike is vertical indicates air in the MC, and pressure bleeding the lever end (as per the instructions) will remove it.( you need a bleed kit for this)
    But aligning the caliper with the brake "on" doesn't quite centre the caliper over the rotor IME.
    Try loosening off the tri align bolts, and the pump the lever a few times to set the pistons, then centre the rotor beween the pads by eye, and tighten the bolts.
    This usually improves the feel, and shortens the "free stroke" before pad contact.

    I find this is a better way to set up all postmount brakes.
    It's nice to be important, but it's more important to be nice.
  • strakstrak Posts: 439
    yep had them zip tied up over night then centralised using the brake on and clamp technique. I may try again with skyliners technique, using feeler guages and eye, but i cant see this reducing the free stroke to be honest.
    Otherwise yep trip to the LBS to get lubed up and bent over. :shock:

    cheers guys
  • Can someone please explain to me how cable tying the brake on and leaving it overnight can make any difference to a brakes feel. The system is sealed when the lever is pulled so there is no way any air can move from the system.
    I've read about it so many times and, as a bike techie, I just cant see how it works.

    Ref the issue with the Juicies.....they are very difficult to get perfect as they have multi position mounts with cones etc. We usually let customers run em for a few rides, to bed em in. We ask em to come back for the first service and then spend time centralising the caliper spot on. You will have a long lever stroke until you do this properly.
    Magic

    Riding, wrecking and repairing mtb's for too long!!

    www.about-bikes.com
  • nicklousenicklouse Posts: 81,520 Lives Here
    it can center the pads to the rotor, or the rotor to the pads. so the pads move evenly.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • Sorry Nicklouse, as soon as you release the lever it returns to its original position.

    Theres no way that this procedure can help-if it does then there must be something that I'm missing. Holding a brake on overnight will make no difference to a brake whatsoever.

    If the pads/rotor are not centralised the force will hold them in the correct position as the rotor will flex to match the caliper. When you release the lever the disc will go back to its original state.

    If the pads are not operating evenly within the caliper there is an issue within the caliper.

    Unless you can tell me otherwise, that is.
    Magic

    Riding, wrecking and repairing mtb's for too long!!

    www.about-bikes.com
  • skylinerskyliner Posts: 613
    But if you have air in the system that works it's way into the hose where it's compressible, holding the lever open with the bike upright can allow the air to pass back into the Master Cylinder, restoring brake feel, but not curing the initial problem, which is air in the system.
    It simply relocates it to a "more convenient position" and is only a "quick fix" or short term remedy.
    Bleeding is usually required to completely erradicate the problem.

    ETA the letter "S" in system
    It's nice to be important, but it's more important to be nice.
  • nicklousenicklouse Posts: 81,520 Lives Here
    Sorry Nicklouse, as soon as you release the lever it returns to its original position.

    Theres no way that this procedure can help-if it does then there must be something that I'm missing. Holding a brake on overnight will make no difference to a brake whatsoever.

    If the pads/rotor are not centralised the force will hold them in the correct position as the rotor will flex to match the caliper. When you release the lever the disc will go back to its original state.

    If the pads are not operating evenly within the caliper there is an issue within the caliper.

    Unless you can tell me otherwise, that is.

    it works.

    the pistons move the same amount from where ever they are. so if you have a caliper that is not quite aligned correctly and is moving the disc as the brake is applied. Allowing the rotor to let the pistons to be set at different distances "out" when the lever is released the pistons move back the same amount, so they now when the brake is applied the pads hit the disc at the same time. It is not a cure all but it can help the settling of the brakes. As the brakes settle under normal use this what happens.

    the Air comment by Mr skyliner is also very valid but i will add this it can also "shrink" the size of the air bubbles allowing them to move more easily through the pipes. BUT too much pressure can put the air into the fluid which is one reason some companies mention De-gassing the fluid.

    Dont believe it? fine dont try it.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • skylinerskyliner Posts: 613

    If the pads/rotor are not centralised the force will hold them in the correct position as the rotor will flex to match the caliper. When you release the lever the disc will go back to its original state.
    .

    Unless you can tell me otherwise, that is.

    If the rotor flexes during operation of the brake, the caliper is not correctly centred.
    This usually stems from the notion that applying the brake with the tri-align bolts loosened and then tightening them centres the rotor between the pads.
    In my experience, this has never been the case with any postmount brake since I started working with them in at least 2003 with the BRM525 on Specialized bikes as OEM components, and possibly before that on Trek or other bikes.
    The only way to set up postmount brakes is to loosen the PM fixing bolts, pump the brake lever a few times to set the pistons, and then centre them by eye.
    Then you get a god positive feeling lever, and no pad binding after the 1st ride to correct.
    It's nice to be important, but it's more important to be nice.
  • skylinerskyliner Posts: 613
    De Gassing. I haven't heard that term since my Motocross days. Fond memories flooding back there. But can't override the Rallying and DH/AM.I'm doing now.

    In my post above this, it says you get a god lever feel, this should read "good lever feel"
    Apologies.
    It's nice to be important, but it's more important to be nice.
  • nicklousenicklouse Posts: 81,520 Lives Here
    used to service for a few rally cars years back before i started racing (Tarmac). Oh and have a read of the Avid brake manual as it was them that kind of first made it posible in the MTB world (or should i say Formula with the design).
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • skylinerskyliner Posts: 613
    Yep, saw the presentation at a show recently, but didn't think it was relevent to my experience of PM brakes in this context.
    It's nice to be important, but it's more important to be nice.
  • skylinerskyliner Posts: 613
    Which teams did you crew for BTW?
    It's nice to be important, but it's more important to be nice.
  • nicklousenicklouse Posts: 81,520 Lives Here
    no teams just privateers.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • skylinerskyliner Posts: 613
    That's cool though.
    I have a friend who worked for PRODRIVE on the current antilag system.
    He's got some interesting stories about the development stages of that process!
    And another mate who works for PROMAX on Gp N Mitsi's and other privateer packages.
    Gets me into some otherwise "no go "areas of Rally GB.

    What kind of tarmac racing are you currently in to? Do you compete at Pembrey?
    It's nice to be important, but it's more important to be nice.
  • skylinerskyliner Posts: 613
    Sorry guys, big thread hijack for no apparent reason. I'll take it to PM or E-mail.
    It's nice to be important, but it's more important to be nice.
Sign In or Register to comment.