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258 And Turbo 400

Discussion in 'Jeepster Commando and Commando Tech' started by garage gnome, Nov 26, 2022.

  1. Nov 26, 2022
    garage gnome

    garage gnome ECJ5 welder 2021 Sponsor

    Western MA
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    I found a turbo 400 that will bolt up to the 258 in my Commando. Only thing is, its missing the flex plate and torque convertor. Is the torque convertor the same as a GM application? And where could I find the flex plate?

    I want to put the th400 in for my mom so its easier for her to drive.
     
  2. Nov 26, 2022
    Keys5a

    Keys5a Sponsor

    Florida Keys
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    I’ve never done that combination, but my guess is you need a flexplate from a 258. Most automatics I’ve seen behind a 258 are either a 727 or 998/999, so I don’t know the bolt pattern for the converter will accept the GM pattern.. You will need a converter from a TH400 or maybe a TH350. Most of the TH400’s were behind AMC 304 or 360 V8s, but I’m pretty sure a few were behind the 258s, so you may find the correct flexplate.
    -Donny
     
  3. Nov 27, 2022
    garage gnome

    garage gnome ECJ5 welder 2021 Sponsor

    Western MA
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    According to Novak's site, the th400 was used behind the 258 in the early 70's.
     
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  4. Nov 27, 2022
    Lockman

    Lockman OK.....Now I Get It . 2022 Sponsor 2021 Sponsor

    White City, NY 14617
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    Very Cool......Novak is your best Source here. They can help mate any GM to AMC.
     
  5. Nov 27, 2022
    Keys5a

    Keys5a Sponsor

    Florida Keys
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    They did build this combination (258/TH400), but it was pretty rare. I’m not sure if I have ever seen one back in the day, let alone finding that flex plate today. I may have a parts book to look up the number, if I ever get home for a few days.
    -Donny
     
  6. Nov 27, 2022
    jpflat2a

    jpflat2a what's that noise?

    Riverside CA
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    The 258/T400 combination was used up to 1979 in CJ7s and full size Jeep models.
    The change to Chrysler autos started in 1980.
    Any auto transmission shop can help with the torque converter as the 258 and V8 are the same.
    I would think the flexplate would be avaialable as well. (I do have an NOS 258 flexplate if you strike out looking).
    Just make sure your crankshaft has the centering bushing unique to the T400 installed in the crankshaft.
    The snout of the converter rides/centers into that.
     
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  7. Nov 28, 2022
    garage gnome

    garage gnome ECJ5 welder 2021 Sponsor

    Western MA
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    Thanks for the info. My 258 currently has a T14 behind it, so I am sure it doesn't have the centering bushing. I think Novak offers one.
     
    Lockman likes this.
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