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known issues with SM420?

Discussion in 'Early CJ5 and CJ6 Tech' started by mtntinker, Jul 8, 2004.

  1. mtntinker

    mtntinker New Member

    Ouch!

    I finally gulped and bought an SM420, supposedly freshly re-built. Got it in, linkages all figured out, etc. etc. Had to get it shipped in, not exactly local.

    Test drive time - won't stay in 3rd gear. Period. Checked clutch adjustment, no help. Will have to pull it and send it back for another try.

    Question is, is this a common problem, or just my luck holding bad?
    Any known issues (this, or anything else) with the 420?

    Thanks, wish me luck, supposedly leaving in a week for a week of wheeling the Colo. high country...
     
  2. lafester

    lafester Sponsor

    i have not heard of any known problems with the 420.
    my first one popped out of gear also in 1st and 2nd only in low gear down hill. this one was not rebuilt though. my second one works great with no problems, also not rebuilt.

    where are you wheeling at?

    chris
     
  3. mtntinker

    mtntinker New Member

    Thanks for the info! The guy (in Denver) who built it sent up a different tranny, it's going in today. Here's hoping.

    We haven't finalized the trails yet, fire danger in southern part of the state may close some down. Might have to give up on Blanca, but will likely do Holy Cross, Redcone, etc.
     
  4. Boyink

    Boyink Super Moderator Staff Member

    Sheese Van..what's that net you, about 110:1 crawl?
     
  5. timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    I was curious ... 7.0*3.15*4.88 = 107.6
     
  6. Boyink

    Boyink Super Moderator Staff Member

    7.2:1 on the 420, IIRC.
     
  7. timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

  8. timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Could be assembled wrong, and it's not going into gear fully. Pops out on decelleration, or randomly?
     
  9. Boyink

    Boyink Super Moderator Staff Member

    Ah. Was getting the T18 and 420 confused in my head (distracted with the 6 auction...;)

    7.05 for the 420 looks like..

    http://www.off-road.com/jeep/tech/convtrans/sm420yj/

    So 108:1 for van. Still. Looow!

    I'm looking at 83-ish to 1 on the CJ6, thinking that's probably lower than I need here in MI.
     
  10. Project71-5

    Project71-5 BACON

    I want an SM420, I'm only at 28.44...in fact its lower than that with the 33's :(
     
  11. mtntinker

    mtntinker New Member

    Yep, 108:1 is what I get, too (BWG) And, since I'm still running 31's to keep low, ground speed is way low. Looks like around 4 mph at about 4000 rpm. Interestingly, granny low in high range gives me nearly the same crawl that I originally had in low range!

    But, to me the great hidden gain is a better spread in the top 3 gears, makes for even better use of the OD, plus sync in 3 gears instead of 2! And now with PLoc in front, also ... Yeehaaa!


    Per Tim's question, it just wouldn't stay in at all, couldn't even hold it in.


    Anyway, this old fogey is getting really pumped about the trip, first real trails since she (CJ5) played Rip Van Winkle about 15 years ago. Now if I can just get the bodywork/paint done sometime soon...
    (Still trying to figure out how to post pics)
     
  12. lafester

    lafester Sponsor

    i would love to check out your rig sometime and compare notes. looks like we have very similar taste in building!

    pm or email if interested.

    i am wondering why you chose to have the 420 worked on in denver. i was toying with the idea of having my spare rebuilt somewhere here in loveland.

    chris
     
  13. mtntinker

    mtntinker New Member

    Done - we'll be in touch!

    For all, 2nd tranny works a charm! Dunno what was wrong with the first, but the guy that rebuilt it stood by it, made this one right. This one is the newer case, with ribs, had to grind a bit to clear the drive shaft. But, all seems well now.

    Have Jeep, Will Travel
     
  14. H8PAVMNT

    H8PAVMNT Rub his head for luck

    Prolly ought to edit your sig now Van :D.
     
  15. mtntinker

    mtntinker New Member

  16. lafester

    lafester Sponsor

    great news!

    you are going to have lots of fun on your trip!

    chris
     
  17. Rob C

    Rob C Member

    Van,
    FWIW, I ran into the same problem with my newly rebuilt T14 that I put in my 66. Turns out it was a bent shift fork causing 3rd not to engage fully. Might be worth a try.
     
  18. mtntinker

    mtntinker New Member

    2nd tranny is in, and works fine. Shifts, stays in gear, all that good stuff. Looking hopefull!

    Now to just finish up the new tranny cover/floor pan, shift boots, ... Might make it yet!
     
  19. Rob C

    Rob C Member

    Glad it worked out. Mine had me scratching my head for a couple of months....... :oops: