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SM420 troubles.

Discussion in 'Early CJ5 and CJ6 Tech' started by Corveeper, Sep 13, 2006.

  1. Sep 13, 2006
    Corveeper

    Corveeper Member

    Chanute, Kansas
    Joined:
    Jul 29, 2005
    Messages:
    817
    Anyone know much ‘bout these?
    Mine was jammed up in 3rd gear. I’ve taken it partially apart, enough to get at the speed clutch, hub and synchros, and I’m at a loss as to why it was jammed. The 3rd gear synchro was jammed up under the speed clutch sleeve but after removal both parts look fine as far as I can tell.
    Is it possible that the 3rd & 4th speed clutch keys are worn and allowed the speed clutch sleeve to slip too far over the 3rd gear synchro and speed gear?
    I’ve been work’n with Herm "the Overdrive guy" Tilford via e-mail but that can be slow going since he answers e-mails only when he has time.
    Any help would be appreciated.
     
  2. Sep 13, 2006
    runnamuck

    runnamuck look out!

    hickory, nc
    Joined:
    Nov 7, 2005
    Messages:
    223
    those parts should come in a quality rebuild kit, fwiw.

    have you checked for a bent shift fork or rod? i would think a bent fork is more of you problem. it would force the jam you describe.
     
  3. Sep 13, 2006
    Corveeper

    Corveeper Member

    Chanute, Kansas
    Joined:
    Jul 29, 2005
    Messages:
    817

    What rebuild kit are you look’n at? Seriously, unless I’ve missed something all the rebuild kits I’ve been look’n at have bearings, gaskets, snap rings, and depending on price synchro’s, but none of them have speed clutch hub, springs, keys or sleeve.
    If you could point that out to me, I’d appreciate it.

    Bent shift rail? Doubt it, the shifter moves smoothly through each shift and shows no cosmetic indications of be’n bent.
    Bent shift fork? I don’t know, I’ll look more closely at that. What would be a good way to measure that?
     
  4. Sep 13, 2006
    runnamuck

    runnamuck look out!

    hickory, nc
    Joined:
    Nov 7, 2005
    Messages:
    223
    atk transmission rebuild kit. the ones that most people get are like you say. at work we get atk's through napa. to check the fork the easy way is with two straight edges a square. not a rail if the shifter moves good when removed from the tranny. i would really check the forks. should be esay to see.

    also there is a tranny shop out in cali that has really complete kits also, when i get home i get more info. for now back to work.
     
  5. Sep 13, 2006
    Corveeper

    Corveeper Member

    Chanute, Kansas
    Joined:
    Jul 29, 2005
    Messages:
    817
    Thanks for the response.
    I’ll search up ATK transmission rebuild kits, take a good long look at my 3rd & 4th shifter fork, and see what I can come up with.
     
  6. Sep 14, 2006
    Corveeper

    Corveeper Member

    Chanute, Kansas
    Joined:
    Jul 29, 2005
    Messages:
    817
    Had a good look at the shift mechanism and don’t think it’s a bent fork. It’s pretty hard to measure though since it’s not a straight flush fork, it’s thicker at the base then “waisted” before reaching the fork that actuates the speed clutch. Eye ball’n it, it looks to be ok, at least I can’t find any stress cracks that would make me think it’s been bent.
    I also had a good look at the speed clutch hub and that is showing obvious signs of wear. It makes sense though, I’m run’n a pretty high-strung V-8 and 3rd probably sees the most stress ‘cause of it.
    Anyway, I haven’t heard back from Herm yet, probably have to give’im a call.
     
  7. Sep 14, 2006
    Corveeper

    Corveeper Member

    Chanute, Kansas
    Joined:
    Jul 29, 2005
    Messages:
    817
    Here’s the 3rd & 4th Speed Clutch Hub and Keys.
    I think that part of the function of these keys, besides engaging the synchro, is the keep the hub from sliding out from under the sleeve. Can anyone confirm or deny this?
    What appears to have happened, the hub slid out from under the sleeve allowing the 3rd gear synchro to get further under the sleeve that it should. Once into the groove on the underside of the sleeve, the synchro then turn slightly and this is what had speed clutch sleeve jammed in place until I disassembled it.
    Does this sound reasonable to you transmission guys?
    I hope so, at least that’s the direction I’m headed.
     
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