Results 1 to 16 of 16
  1. #1
    mtbr member
    Reputation:
    Join Date
    Nov 2008
    Posts
    47

    New question here. Magura Louise '08 bite point problem

    Hello, I own Magura Louise disk brakes and I noticed this (in my opinion) strange behaviour:

    1. When I press the lever for the first time it moves for a certain amount
    2. Then I quickly press and release the lever few times
    3. The bite point has changed, the lever moves noticeable less then in step 1)
    4. After the lever has been released and then pressed after few moments it moves as in step 1)


    In fact, as press and release the lever, point in which brake pads engage the rotor changes.

    The brake is brand new. This problem occurs while I am riding or standing, so heat is not the issue.

    Could you please advise me about this problem?
    Thanks.

  2. #2
    mtbr member
    Reputation: Stevirey's Avatar
    Join Date
    Jul 2005
    Posts
    702

    brake point

    I'd ask a tech at the Magura web site.

  3. #3
    mtbr member
    Reputation: Wombat's Avatar
    Join Date
    Jan 2004
    Posts
    1,754
    There is air in the system and you are compressing it when you pump the lever. After you stop pumping it returns to its uncompressed state. You need to bleed the brakes.

    Tim

  4. #4
    mtbr member
    Reputation: itsdoable's Avatar
    Join Date
    Jan 2004
    Posts
    1,874
    Most brakes do this to some extent, I've notice maguras seem to do it more, but that may have been with the old thicker fluid.

    The caliper pistons retract slowly - in that they retract slower than your lever. Your master is an open system, so if the pistons have not completely retracted yet, squeezing the lever again starts pushing the pistons back in from where they were, and thus you engage earlier at the lever. Waiting a few seconds allows the pistons to fully retract, and you get the original feel.

    This occurs more often when there is excess lever travel, which is sometimes the caliper pistons not auto-adjusting, and sometimes cause by a tiny amount of air in the system.

    Air in the system usually causes your lever to need more travel to move the pistons. Levers to the bar without engagement is a classic air in the lines symptom.

    If there is a tiny amount of air, you can just use the brakes normally and live with the weird lever play. Over a short time, the air will make it's way up to the reservoir, and effect will go away, or be minimized. Then you can open the reservoir and burp the system. You can also do a full bleed, but that may just re-introduce a bit of air in there (usually bleeds leave a tiny bit behind).

  5. #5
    mtbr member
    Reputation:
    Join Date
    Nov 2008
    Posts
    47
    Thank you for your replays.

    I just got my brakes bled and they work much better. Also they put a little more oil to reduce lever travel to give me firmer fill and to allow me to adjust lever closer to the handlebar. Now, I am pleased how they work and I am looking forward testing them in snow and mud.

    Thanks!

  6. #6
    ...idios...
    Reputation: SteveUK's Avatar
    Join Date
    Apr 2006
    Posts
    5,680
    "Also they put a little more oil to reduce lever travel to give me firmer fill and to allow me to adjust lever closer to the handlebar."

    Then they've over-filled your system. Don't be surprised if one problem has been replaced by another - which will be that your brake starts to bind during/after braking descents.
    .
    .


    What luck for rulers, that men do not think - Adolf Hitler

  7. #7
    mtbr member
    Reputation:
    Join Date
    Nov 2008
    Posts
    47
    Quote Originally Posted by SteveUK
    Then they've over-filled your system. Don't be surprised if one problem has been replaced by another - which will be that your brake starts to bind during/after braking descents.
    I hope that it will be ok.

    Before I couldn’t adjust reach to fit my hand size because when braking lever would come too close to the handlebar. Now is just fine.

    I will test it this weekend on local hill/mountain.

  8. #8
    mtbr member
    Reputation: itsdoable's Avatar
    Join Date
    Jan 2004
    Posts
    1,874
    Quote Originally Posted by SteveUK
    Then they've over-filled your system....
    They may have been underfilled to start with, then the bladder in the reservoir tends to cause the pistons to retract a bit more when the compensation port is open.

    This also happens when the pads are worn, as you need more fluid down at the caliper, and it thus sucks the reservoir bladder in. I've found that some Maguras tend to start doing this when the pad still had some life left (~1/3) - a consequence of minimizing fluid volume to save weight. You can replace the pads, or top up the reservoir. If you top up the reservoir, you just have to remember to burp some fluid out then you change the pads.

  9. #9
    mtbr member
    Reputation:
    Join Date
    Nov 2008
    Posts
    47
    Quote Originally Posted by itsdoable
    They may have been underfilled to start with, then the bladder in the reservoir tends to cause the pistons to retract a bit more when the compensation port is open.
    Hm.
    The brakes are brand new, originally bled by Magura, pads are new. Maybe they did come underfilled or some oil escaped while installing and shortening the hose.

  10. #10
    ...idios...
    Reputation: SteveUK's Avatar
    Join Date
    Apr 2006
    Posts
    5,680
    "They may have been underfilled to start with, then the bladder in the reservoir tends to cause the pistons to retract a bit more when the compensation port is open."

    It's not possible to know whether or not they started out under-filled. I doubt very much that there would be enough vacuum pressure at the MC diaphragm to retract the pistons, an assertion that you agree with in your next sentence...

    "...as you need more fluid down at the caliper, and it thus sucks the reservoir bladder in."

    If the fluid has been 'topped up' when the pistons/pads have extended to their working position, which is what I understood to have happend from purple dog's post, then the system is over-filled an more likely to suffer from problems during periods of continuous braking. It's pointless for us to ruminate - the OP could check with the shop to confirm exactly what they've done. Perhaps they thought, as many do, that they could shorten the hose without bleeding afterwards?
    .
    .


    What luck for rulers, that men do not think - Adolf Hitler

  11. #11
    mtbr member
    Reputation:
    Join Date
    Nov 2008
    Posts
    47
    Quote Originally Posted by SteveUK
    If the fluid has been 'topped up' when the pistons/pads have extended to their working position, which is what I understood to have happend from purple dog's post, then the system is over-filled an more likely to suffer from problems during periods of continuous braking.
    No, they didn't just 'topped up' the fluid, they bled the brakes putting a little more fluid so I could use the brakes – dial reach adjust to suit my hand size and that lever would not almost touch the handlebar (as it was before).

    Quote Originally Posted by SteveUK
    Perhaps they thought, as many do, that they could shorten the hose without bleeding afterwards?
    Yes, first time while instaling the brakes they didn’t bled after shortening the hose.

  12. #12
    ...idios...
    Reputation: SteveUK's Avatar
    Join Date
    Apr 2006
    Posts
    5,680
    "Yes, first time while instaling the brakes they didn’t bled after shortening the hose."

    In which case there was air in the system, creating the list of problems in your original post. I hope the shop hasn't charged you for attending to their own incompetence?
    .
    .


    What luck for rulers, that men do not think - Adolf Hitler

  13. #13
    mtbr member
    Reputation:
    Join Date
    Nov 2008
    Posts
    47
    Quote Originally Posted by SteveUK
    In which case there was air in the system, creating the list of problems in your original post. I hope the shop hasn't charged you for attending to their own incompetence?
    No they didn't. But I wouldn't be so harsh.
    I was (and still am) their customer for many years and they proved to be competent and fair.

  14. #14
    mtbr member
    Reputation: itsdoable's Avatar
    Join Date
    Jan 2004
    Posts
    1,874
    Shortening hoses without bleeding is an old Magura trick that goes back almost 10 years. You usually have to burp the reservoir, but it works fine if done correctly. It was documented on the old Magura Cult page, which closed early this year.

    Topping up the reservoir to use the last bit of pad is also an old trick, especially for those of us riding in sub-zero temps. If the brakes were bled with the pistons fully retracted, and you looked at the MC diaphragm under the cover when the pads are ~60% worn, it is sucked most of the way into the reservoir. And it does cause the pistons to retract more than necessary. Topping up the fluid till the diaphragm is neutral fixes the lever problem. Since the diaphragm is now neutral, there is still plenty of space for expansion. You just cannot retract the pistons completely to insert new pad until you burp the reservoir (This was also the case with the old Hayes brakes). Those that don't like playing with the fluid just replace the pads at that point.

  15. #15
    ...idios...
    Reputation: SteveUK's Avatar
    Join Date
    Apr 2006
    Posts
    5,680
    "I was (and still am) their customer for many years and they proved to be competent and fair."

    That is, of course, your prerogative, and I don't doubt that it's possible to do this "Magura trick", but the fact that they shortened a hose and didn't even check to make sure that it didn't need bleeding demonstrates a lack of competence. Agreed, it's not the end of the world, especially when they're doing a job that you can't/won't, but it's poor service all the same. Half a job, one might say.
    .
    .


    What luck for rulers, that men do not think - Adolf Hitler

  16. #16
    mtbr member
    Reputation:
    Join Date
    Nov 2008
    Posts
    47
    Quote Originally Posted by purple dog
    I will test it this weekend on local hill/mountain.
    I spent most of the Saturday and Sunday riding in mud, rain and some snow – brakes preformed flawlessly.

    Cheers!

Posting Permissions

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