Sm420/tranny tunnel clearance issue

Discussion in '40- & 55-Series Tech' started by CruisinGA, Jul 2, 2005.

  1. CruisinGA

    CruisinGA

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    I'm down at ULC in the middle of boltin up the SM420. In about 15 min the engine/tranny/tcase will be out of the truck.

    Before I get there, should I plan on interference between the SM420 top plate and the tranny tunnel? It has the hole for a 3spd shifter...

    Asking so that I can go ahead and yank the tunnel if there is a clearance problem before finding out as I am slipping the long block back in the truck.

    Thanks!
     
  2. Pin_Head

    Pin_Head

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    It is pretty hard to get the sm420 in with a 4sp tunnel. My prediction is that you will need to
    either remove the tunnel or drop the rear motor mounts for more clearance. Your choice.
     
  3. CruisinGA

    CruisinGA

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    Its a 3 spd tunnel...

    (early '74 truck)
     
  4. Pin_Head

    Pin_Head

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    My point was that I don't have any experience with a 3sp tunnel and the 420. From my experience with the 4sp cover, I don't think that the situation will be any better with the 3sp cover. If you remove the rear motor mounts and swing the tranny shift tower up into the hole, it may work (if the hole is in the right place). You can't just slide it straight back with the tunnel cover in place and get the tower in the hole because it is too high above the sheet metal by about 2-3 inches.
     
  5. CruisinGA

    CruisinGA

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    Ok, sorry I did not catch your point.

    We just pulled the tranny tunnel anyway.

    Thanks!

    (BTW Charlie- your writeup has been my SM420 bible, I've probably read it 100 times over the last 2 years) :cheers:
     
  6. mr_manny

    mr_manny

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    When I installed my 465, I also pulled mine.

    when you get tired of the open floor, it will be time to modify your 3spd tunnel.

    Took lots of measurements and removed as little as possible from the stock tranny tunnel
    (several trial fittings where required to get this right).
    I then made a sheet metal cover that was welded on top of my tunnel.

    Really happy with the results,
    manny
     
  7. Poser

    Poser Oh...Durka Durka Durka. s-Moderator Supporting Vendor

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    465 trannies are taller than a 420.


    420 tower should fit into the same hole as a three speed tranny opening on the tunnel....least it did on mine...


    Good luck!


    -Steve
     
  8. Pin_Head

    Pin_Head

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    Geez, if you had to read it 100 times it must be pretty bad. I have been meaning to update it to include rebuilding the transfer case.

    The 420 shift tower fits into the 4sp tunnel cover hole with no cuting too, so they must be pretty much the same.
     
  9. 73lndcrsr

    73lndcrsr

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    I had to modify mine for the 420 to fit. I only had to take an inch or so all the way around. I did not do any body lift.

    I just made a new shifter boot for it and it works fine.

    The 420 is great off road, I love the low gearing.
     
  10. CruisinGA

    CruisinGA

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    Got a few small additions (parts list/ numbers etc) I want to send you for your review Charlie. I rebuilt a spare tcase, just used the FSM.


    Good deal on the tranny tunnel.

    One more question- I tried both some 1/2"-20 bolts and the Metric bolts that came out of the 3spd in the lower tapped holes in the SM420. Neither threaded in very well. Is 1/2"-20 supposed to be correct?
     
  11. Pin_Head

    Pin_Head

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    The lower holes thrreaded in the sm420 ears are half inch SAE coarse thread. The upper bolts are fine thread.
     
  12. CruisinGA

    CruisinGA

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    Good deal.

    Thanks again Charlie.

    I think it would have saved you some time if you had just flown down to Atlanta and stood there while I installed the 420. :D
     
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