Results 1 to 10 of 10

Thread: Lefty Knock

  1. #1
    mtbr member
    Reputation:
    Join Date
    Aug 2006
    Posts
    16

    Lefty Knock

    When I lower the SPV pressure to near the min. 30 psi on my Lefty Max 140 SPV I can hear a knocking while riding. By 50 psi it is pretty much gone. The knock is not a top out or bottom out, not related to bearing migration, and happens at the exact moment following a bump when the "fork" travel reverses from compression to rebound. Unfortunately, I like the way the "fork" feels with only 30 psi in it.

    Two questions:
    1) What causes the knock?
    2) Do they all do this?
    3) Will I damage something in the system by allowing it to knock?

  2. #2
    All Lefty's, all the time Moderator
    Reputation: MendonCycleSmith's Avatar
    Join Date
    Feb 2005
    Posts
    12,622
    Most likely, the fork has air in the oil. A well executed oil change and bleed, should resolve the issue.
    This is a Pugs not some carbon wannabee pretzel wagon!!

    - FrostyStruthers



    www.mendoncyclesmith.com

  3. #3
    LA CHÈVRE
    Reputation: Dan Gerous's Avatar
    Join Date
    Feb 2004
    Posts
    9,380
    But SPV forks do make a clicking sound with too low pressures. Too low is close to or under 30PSI, it shouldn't be there at 35 or more. If it still does it at higher pressures..... I'd guess Mendon is right.

    DAN.GEROUS.NET : MOUNTAIN BIKING : CYCLOCROSS : ROAD :

  4. #4
    mtbr member
    Reputation:
    Join Date
    Aug 2006
    Posts
    16
    Up till a few months ago my Lefty kept losing SPV air pressure every week, then I changed the oil and found it to be dark, burnt, and foamy. With the oil change I used the OE oil and followed the instructions on this forum, being sure to purge air and fill completely to the top. No more SPV pressure lost! I think that was caused by having too much air and compressability above the SPV bladder.

    What it did and still does however, is knock at the lower pressures. It definitely goes away the higher I set the SPV, but I like the lower SPV pressure ride qualities. Intuition tells me that knocking is metal on metal, and this is never good, so I'm assuming I should keep enough air in it that it doesn't knock. Thoughts?

    What actually causes the knocking? I've never had the damper assembly disassembled to know. Is it a valving/shim pack slamming shut? I'm guesing the SPV pressure keeps something seated or closed and it is being allowed to come open. If anyone wants to take the time to explain thsi to me I'd love it.
    Last edited by DDDDylan; 08-03-2007 at 08:12 AM.

  5. #5
    LA CHÈVRE
    Reputation: Dan Gerous's Avatar
    Join Date
    Feb 2004
    Posts
    9,380
    Found this thread explaining why SPV forks make that sound... Not enough SPV pressure, no rebound, top outs... I think I remember a similar explanation a while back. If it's a top out, I think it's more annoying than damaging but I'd rather avoid it...
    Last edited by Dan Gerous; 08-03-2007 at 01:14 PM.

    DAN.GEROUS.NET : MOUNTAIN BIKING : CYCLOCROSS : ROAD :

  6. #6
    mtbr member
    Reputation:
    Join Date
    Aug 2006
    Posts
    16
    OK, thanks. Sounds common. I think I still want to run enough pressure to avoid the noise. It is DEFINITELY not a top-out issue. It sounds like nobody knows exactly what the mechanics are.

  7. #7
    All Lefty's, all the time Moderator
    Reputation: MendonCycleSmith's Avatar
    Join Date
    Feb 2005
    Posts
    12,622
    Quote Originally Posted by DDDDylan
    OK, thanks. Sounds common. I think I still want to run enough pressure to avoid the noise. It is DEFINITELY not a top-out issue. It sounds like nobody knows exactly what the mechanics are.

    Well, it's not that we don't know the mechanics, it's that there are sooooo many variables, and different folks, explain and experience things so differently. One persons horrible noise, is anothers thing they just ignore As for the noise, oil level, next to top out (and SPV pressure), is the most common cause, top it off, and bleed it, most likely it will go away
    This is a Pugs not some carbon wannabee pretzel wagon!!

    - FrostyStruthers



    www.mendoncyclesmith.com

  8. #8
    mtbr member
    Reputation:
    Join Date
    Aug 2006
    Posts
    16
    -"It sounds like nobody knows exactly what the mechanics are."

    Sorry, I didn't mean that to sound condescending.

  9. #9
    All Lefty's, all the time Moderator
    Reputation: MendonCycleSmith's Avatar
    Join Date
    Feb 2005
    Posts
    12,622
    Quote Originally Posted by DDDDylan
    -"It sounds like nobody knows exactly what the mechanics are."

    Sorry, I didn't mean that to sound condescending.
    No worries, just want to make sure you're happy
    This is a Pugs not some carbon wannabee pretzel wagon!!

    - FrostyStruthers



    www.mendoncyclesmith.com

  10. #10
    mtbr member
    Reputation:
    Join Date
    Jul 2006
    Posts
    95

    spv volume

    try turning the spv volume adjustment in and then lowering the spv air pressure. It worked for me, now I only get a knock when the bearings migrate

Posting Permissions

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