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Sm420 Questions

Discussion in 'Early CJ-5 and CJ-6 Tech' started by Cowboyjeeper, Jul 4, 2019.

  1. Jul 4, 2019
    Cowboyjeeper

    Cowboyjeeper Member

    Show low az
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    good morning happy 4th.

    I have an opportunity to get an sm420 for a very good deal but I have some questions before I go to look at it,
    1. How to Id what year it is if that is a big deal
    2. What to look for to tell condition? And when I pull the top.
    3. Are parts even still available should I need to rebuild?
    4. How hard are bell housings to find I have a small block already.
    5. I know Novak makes the t-case adapters, but I have what I think is a Saginaw or Muncie car trans now, how big of a job am I getting myself into?

    Thnaks again
     
  2. Jul 4, 2019
    sgogpn

    sgogpn Member Sponsor 2019 Sponsor

    Glendale, AZ.
    Joined:
    Nov 20, 2002
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    If you check Novak’s Knowledge base it will detail the 3 different iterations of the 420 over the years. Most internal parts are still available and Novak’s rebuild kits are very good.
    As far as swapping from a car 4 speed to the 420 your current bellhousing should work. You will have to measure to see the difference in length between the two to determine where your crossmember will end up. Any change in crossmember location will require your driveshaft lengths to be changed, as well as floorpan modifications.
    While there is work involved in any swap, the benefits of a granny low in a Jeep cannot be overstated. You’ll love it when you’re done. :)

    Good luck with your swap; keep us posted.

    Mike
     
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  3. Jul 4, 2019
    Cowboyjeeper

    Cowboyjeeper Member

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    I’ll go read that section from Novak. I agree a granny gear is a great thing in a Jeep. I had a sm420 in a flattie when I was younger it was a great setup. Would be nice if I could just use the bell housing I have. I figured the drivelines would change. Also any idea if my pto winch can still work?
     
  4. Jul 4, 2019
    Muzikp

    Muzikp Sponsor Sponsor

    Sacramento Ca.
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    I have a SM420 in mine and love it. But they are big and heavy. It will require some modifications to your floor so if you are trying to keep the tub all original it will be difficult.
     
  5. Jul 4, 2019
    Cowboyjeeper

    Cowboyjeeper Member

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    No trying to keep all original PO already cut it up to put a car 4speed in. I can make a nice cover. The good thing about big n heavy is less likely to break
     
  6. Jul 4, 2019
    sgogpn

    sgogpn Member Sponsor 2019 Sponsor

    Glendale, AZ.
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    Your PTO winch should still work as it’s driven off the transfer case. You might need to check the driveline to the winch from the PTO to see if the 420 will interfere with it.

    Mike
     
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  7. Jul 4, 2019
    Muzikp

    Muzikp Sponsor Sponsor

    Sacramento Ca.
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    I’ve heard some people have a clearance issue with the front driveshaft hitting the tranny but mine doesn’t seem to have an issue.
     
  8. Jul 4, 2019
    Cowboyjeeper

    Cowboyjeeper Member

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    Maybe casting differences? Any ideas on the length difference compared to the Saginaw car trans?
     
  9. Jul 4, 2019
    Muzikp

    Muzikp Sponsor Sponsor

    Sacramento Ca.
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    Yeh I think some 420’s have a hump on the passenger side that interferes, I’ve read about it on this forum somewhere. I’m not home or I would measure mine. There are several pics in my build thread of the tranny but not the installation process.
     
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  10. Jul 5, 2019
    Cowboyjeeper

    Cowboyjeeper Member

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    Well I went and got that trans. It looks pretty good shifts well. Anything specific I should look for? Or just rebuild it for good measure? I know these things are pretty tough.
     
  11. Jul 5, 2019
    sgogpn

    sgogpn Member Sponsor 2019 Sponsor

    Glendale, AZ.
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    Just check for the usual things; abnormal wear, pitting, broken gear teeth, chewed up thrust bearings, worn shifter pins, etc. If you order a Novak kit, ask them to verify that the kit for your 420 needs 2 synchros. The last time I went through one of mine recently there was only 1 new synchro in the kit; to their credit they sent one right out.

    Mike
     
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  12. Jul 5, 2019
    jpflat2a

    jpflat2a what's that noise?

    Riverside CA
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    Me, I would rebuild/go thru it. That way I know what shape it's in.
    Otherwise, it's roll of the dice.
    Do you feel lucky ?
     
  13. Jul 5, 2019
    Cowboyjeeper

    Cowboyjeeper Member

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    Was thinking just getting a Novak kit for good measure since I don’t need it right this second.
    Still need an adapter and stuff to install.

    It does have good teeth and is smooth. Where are the shift pins? What I looked at isn’t too worn.
     
  14. Jul 5, 2019
    sgogpn

    sgogpn Member Sponsor 2019 Sponsor

    Glendale, AZ.
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    They are the 2 pins on either side of the shift tower that the shifter grooves ride in (for lack of a better description). Sometimes the pins can work loose or get worn, causing shifter slop. the grooves in the shifter can also get worn, contributing to the slop...

    Mike
     
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  15. Jul 5, 2019
    Cowboyjeeper

    Cowboyjeeper Member

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    Sgogpn oh I know what you mean those are good and tight as well as the shifter is tight too. It actually looks good.

    If anyone anywhere near AZ has a sm420 to d 18 adapter they need a new home for pm me.
    Thanks everyone for all the help.
     

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