1. Registration trouble? Please use the "Contact Us" link at the bottom right corner of the page and your issue will be resolved.
    Dismiss Notice

sm420 problem

Discussion in 'Early CJ5 and CJ6 Tech' started by AKCJ, Feb 1, 2005.

  1. Feb 1, 2005
    AKCJ

    AKCJ Active Member

    Fairbanks, Alaska
    Joined:
    Aug 12, 2003
    Messages:
    1,035
    Problem 1. I had a load "bang" noise from under the Jeep 3 times in 2 months. Sounded like someone hit something with a sledge hammer. I tried to ignore it the first two times but after the third there was a very slight ticking noise from the tranny (sm420) while in 3rd or 4th gear - about 1 tick per 1 or 2 seconds. Pulled the center out of the floor and pulled the top off the tranny looking for a broken gear tooth. Can't see any damage but now:
    Problem 2. While looking at all the gears I slid the front shift collar forward to see better. Now it won't come back! Dang. I've really pulled hard and tried to (carefully) pry it back but it is stuck. It will move but just will not go back to where it should be.

    Any ideas?
     
  2. Feb 2, 2005
    msbweiland

    msbweiland Member

    Yakima, WA
    Joined:
    Oct 26, 2002
    Messages:
    80
    Might be a broken shift dog or blocking ring?
     
  3. Feb 2, 2005
    AKCJ

    AKCJ Active Member

    Fairbanks, Alaska
    Joined:
    Aug 12, 2003
    Messages:
    1,035
    Looking at sm420 diagram. Not seeing "shift dog" or "blocking ring". Were you refering to problem 1 or problem 2? I'm not really a transmission guy - but I know what one is when I see it.

    And, I meant to say loud bang in the first post (not load bang!).
     
  4. Feb 2, 2005
    AKCJ

    AKCJ Active Member

    Fairbanks, Alaska
    Joined:
    Aug 12, 2003
    Messages:
    1,035
    OK. After an extensive search I found some info on the loud bang. Steve in CO (CJ6/Nisson guy) mentioned these trannys "binding up and releasing with a loud bang". His solution was graphite etc.. Anyway, that's good enough for me on problem 1. I'm still unable to put it back in service due to problem 2 - shift collar won't slide back.

    I've got the t-case in neutral and have put a strap on to hold down the clutch pedal. I can easily turn gears by hand - no binding. Everything is great except for shift collar - also called "3rd and 4th speed clutch sleeve" in the book.

    What do you guys think?


    1970 CJ-5, 225 V-6, headers, HEI, PS, D30 Fr, 44 Rr, ARB's, SM420 w/ Novak, D18 single stick, 33" TSL Radials, Ramsey REP 5000, Sky Jacker Soft Ride,
     
  5. Feb 2, 2005
    Boyink

    Boyink Super Moderator Staff Member

    Tulsa, OK
    Joined:
    Sep 20, 2002
    Messages:
    6,193
    I've had the "tranny bang" experience... :shock: I caused it by staying in 4WD on a road that grew hard-packed after I shifted in the front axle. Soon I had the bang!, enough of a jolt to kill the engine, and I thought the Jeep was toast. Visual inspection was OK...started it up and drove on w/o issue.
     
  6. Feb 2, 2005
    AKCJ

    AKCJ Active Member

    Fairbanks, Alaska
    Joined:
    Aug 12, 2003
    Messages:
    1,035
    Thanks Boyink,
    RE: big bang,
    First one was in Sept. during a trail ride - dirt trail, I think in 4WD.
    Second in Nov. on slick, icy, snow road - in 4WD for sure.
    Third in Nov. slightly icy road - possibly 4WD but not sure.

    It's good to hear that the noise may not be worth getting too worried about.
     
  7. Feb 2, 2005
    maxx

    maxx Banned

    Menlo Park, Ca
    Joined:
    Apr 22, 2003
    Messages:
    171
    Just a shot in the dark suggestion. If you havent got it to shift, why not try to put the shifter into the appropriate gear it is stuck in, and try to get the cover back on? The 420 gears are huge and heavy, and need to be tugged in the right points with the right amount of force.

    As far as the ticking, its hard to make a guess without hearing it/being there. Does it do it with clutch in or out? You said in 3rd or 4th. Does it make the tick while stopped?

    Last ditch effort would be to email Herm the overdrive guy. He rebuilds 420s among many other things, and might have some insight. Keep us posted on the outcome ok?
     
  8. Feb 3, 2005
    AKCJ

    AKCJ Active Member

    Fairbanks, Alaska
    Joined:
    Aug 12, 2003
    Messages:
    1,035
    maxx thanks for the ideas

    -Tried putting the cover back on but even with the lever in 4th the shift fork will not go far enough forward to go in to the groove in the shift collar. I had hoped to use the gear shift lever to get this sucker to move.

    -Ticking. The frequency is what seems strange to me. What goes around only one time every 1 or 2 seconds? while in 3rd or 4th gear? And it's the same frequency in 3rd or 4th gear. Only does it when the vehicle is moving - not when stopped. It does it for sure with the clutch out - I only drove it this way from work to home - about 4 miles. Not sure if it happens while moving with clutch pushed in but I think yes.

    -Good idea asking Herm. I'll email him ASAP.
     
  9. Feb 3, 2005
    lafester

    lafester Sponsor

    loveland, co
    Joined:
    Sep 24, 2002
    Messages:
    260
    have you drained the oil to see if there is anything at the bottom preventing the gear to slide forward? synchros look good?

    chris
     
  10. Feb 3, 2005
    AKCJ

    AKCJ Active Member

    Fairbanks, Alaska
    Joined:
    Aug 12, 2003
    Messages:
    1,035
    Yes the oil is out. Yes synchros look good. Nothing in bottom.

    I emailed with Herm today. I now think the shift dogs have slid too far forward. I need to push in on all three of them at the same time while slightly rotating the main shaft to get the shift collar to slide towards the back where it belongs. Herm gave me a written description.

    The first reply to this thread (from msbweiland) refered to shift dogs but I didn't know what they were.

    Work is getting in the way of my Jeep time this week so it will be a day or two before I can get out to the garage before 10PM.
     
  11. Feb 4, 2005
    msbweiland

    msbweiland Member

    Yakima, WA
    Joined:
    Oct 26, 2002
    Messages:
    80
    There is usually a reason they slide forward. The dogs are held in place by a spring/clip from underneath (from what I can remember). I'd bet one of them broke, allowing the dogs to slide forward.
    The blocking rings are the brass syncros. I would bet the 4th gear ring is at the very least cracked if not broken. There isn't any place for the dogs to go unless they break the ring. I'd check it VERY closely before you seal it back up.
    When in doubt, tear it apart. 8)
     
  12. Feb 7, 2005
    AKCJ

    AKCJ Active Member

    Fairbanks, Alaska
    Joined:
    Aug 12, 2003
    Messages:
    1,035
    Update.
    Finally! got it to slide back into place but it wasn't easy.
    Ended up making a jig to mount a thick metal strap across the top of the tranny. I drilled two holes (before mounting it of course) in the strap to put pry bars through. Using this setup (and some creative language) I finally got it just right to make it slide. One pry bar on each side of the shift collar. Kinda like a makeshift shift fork. Seemed like it took a lot of force but I can't find anything broken. I'll look at it some more before I put in the fluid and put the top back on.
    Jerry
     
  13. Feb 7, 2005
    maxx

    maxx Banned

    Menlo Park, Ca
    Joined:
    Apr 22, 2003
    Messages:
    171
    Ingenious solution. Hope its ok. Let us know.
     
  14. Mar 1, 2005
    AKCJ

    AKCJ Active Member

    Fairbanks, Alaska
    Joined:
    Aug 12, 2003
    Messages:
    1,035
    Well, good news bad news.

    Got the tranny all buttoned up, put the floor all back in no trouble. Decided to take another look in the t-case since I couldn't find anything wrong in the tranny.

    Wow. Broken gear teeth in the t-case.

    I'll start another post with new title "Dana 18 problem".

    Here's a picture of the setup for moving the stuck shift collar.
     
New Posts