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Another Cold Day And I'm Chasing Another Rabbit

Discussion in 'Jeepster Commando and Commando Tech' started by ANTHONY DRANE, Feb 5, 2022.

  1. Feb 5, 2022
    ANTHONY DRANE

    ANTHONY DRANE New Member

    Friendly, WV
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    I want to do a TDI conversion on my 67 JC. The pre made adapters are from TDI to Chevy TH400 but Jeep used the BOP TH400 so only the bottom bolt and alignment dowel are the same. All the other bolt holes mismatch. I can have an adapter made if I have accurate measurements. Does anybody here have an accurate drawing with good measurements of the BOP TH400 bellhousing. What I've found online omits referencing the crank centerline to any height measurements. Width is there but no height. I think Chevy measures 2.32" from crank center to dowel center but that's unconfirmed. BOP should be the same though, if it's correct. Thanks
     
  2. Feb 5, 2022
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Jeep never used the BOP TH400. All their Buick engines used a nailhead/universal transmission with a ring adapter and in some cases a bushing for the crank snout. Look at the J-series parts book. The 225 and 350 will be the same.

    If you do not understand what this means, I can elaborate.

    A Chevy TH400 should be easy to come by. Transfer the Jeep output shaft to the Chevy case. I don't recall the details - the Chevy output may bolt up to the Jeep transfer case adapter, and not have to transfer the output shaft.
     
    Last edited: Feb 5, 2022
  3. Feb 5, 2022
    ANTHONY DRANE

    ANTHONY DRANE New Member

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    OK. I've gotten some bad info and ran with it. Are you saying that the rear of the buick V6 in my JC is the same as a chevy 350? I found this, https://www.jeeptech.com/trans/th400.html and misread it. If it has a chevy 350/400 pattern, I'm good.
     
  4. Feb 5, 2022
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    No. The Chevy, BOP and nailhead cases are all different.

    If you want a Chevrolet pattern, you need a Chevrolet case. There are adapters from the BOP to the Chevrolet pattern, but you have neither with a Jeepster. You have a nailhead that's adapted to the BOP pattern using a ring adapter. I suppose you could go from the nailhead to the BOP adapter to a Chevrolet adapter, but I'm not sure how the convertor support would work out.
     
  5. Feb 5, 2022
    ANTHONY DRANE

    ANTHONY DRANE New Member

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    No. This is getting out of hand. I wanted to be able to switch back to stock motor/trans if The notion took me. I'd be way ahead to just pull the motor trans as a unit and set it aside, buy a 700r4 and adapt my TDI to it. Man, just being a little off can be a lot of trouble. I think I'll put a bug in my transmissions guys ear and let him be the brains. I'll just take his good advice and keep my OEM motor/trans under a tarp in the garage. Thanks. This is easier anyway.
     
  6. Feb 5, 2022
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Jeep bought the nailhead transmission from GM, and adapted it to their engines. They used several engines ahead of the TH400, each with its own ring adapter.

    Look at the Buick nailhead engines. The nailhead block sticks out to meet the transmission case, providing the extra length needed (ie a shorter TH400 case) to adapt to other engines. Jeep adapted the same transmission to the AMC 327, Buick 350, Buick 225, Rambler 232, AMC 258, AMC 304 and AMC 360. They used a different ring adapter for each, and sometimes a bushing to support the convertor.

    If you need a Chevrolet pattern TH400, the obvious route (to me) is to source a Chevy TH400 and install whatever output shaft is needed for the Dana 20.
     
  7. Feb 5, 2022
    ANTHONY DRANE

    ANTHONY DRANE New Member

    Friendly, WV
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    I was wondering if I could use my D20 on another GM trans. I'm a Mopar guy and know a lot of that stuff in my sleep. (kinda why I stuck to it.) I've got a lot to learn. My trans guy is heavy into GM an 4x4s. I'm betting he can fix me up with something he. or a buddy of his has, for less than I'd have in rebuilding my OEM trans. I'm learning.
     
  8. Feb 5, 2022
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    I don't know offhand. You need a TH400 output shaft with the right spline count to match your input gear to the Dana 20. Look on the Novak site - they have a table of Dana 20 input gears that you can match with what you have.

    There are passenger-drop NP241s as I recall; the NP241C, though I don't think that's enough specification to guarantee passenger drop. Ask your transmission guy. You also need to worry about the narrow chassis width of the C101 and a chain-drive transfer case. The Dana 20 will be ok, regardless.
     
  9. Feb 5, 2022
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Seems unlikely. The D20 adapter has the "texas pattern" which is only compatible with the Dana 20 and Dana 18. If you go with something later, like the Dana 300, you'll have the round New Process pattern, which can mate to other transfer cases.
     
  10. Feb 5, 2022
    ANTHONY DRANE

    ANTHONY DRANE New Member

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    Man, I'm in uncharted water. I'll talk Jason and get his advice on how I should proceed. Look how much easier this would have been If I'd been happy to leave the V6. NOOO not me, I gota be different. It will be fun in the end and worth the effort. I hope. :)
     
    Tom_Hartz likes this.
  11. Feb 6, 2022
    Lockman

    Lockman OK.....Now I Get It . 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    timgr is very, very knowledgeable on the tech stuff . If I may suggest : https://www.novak-adapt.com ,also . Great reference site & when you call , they have a ton of knowledge & experience. They've seen it all before.
     
    Last edited: Feb 6, 2022
  12. Feb 6, 2022
    Fireball

    Fireball Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    It shouldn't be that hard to find a Chevy tubo 400 case to swap your guts into. They made literally millions of them.
     
  13. Feb 6, 2022
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Thanks for the vote of confidence ... there's plenty I don't know about this topic.

    The OP seems a little lost, so I will recap if I may.

    I am quite sure about the TH400 case types. Realize that there is the transmission, an adapter, and the transfer case. If you stay with the original transfer case (a Dana 20), the bare transmission has an output shaft that must mate to the splines of the drive gear of the transfer case. The Jeep TH400 has a 15 spline output shaft, which goes through the adapter and into the transfer case drive gear. The adapter converts the rear pattern of the bare transmission to the "texas" pattern (sort-of looks like the state of Texas) of the Dana 20.

    The most straightforward way to get the Chevrolet pattern that you want for your TDI adapter is to use a Chevrolet TH400. That's what I would do. There were a lot of them made, and it should be easy to find a core. I would build a transmission, since I think that kind of work is fun, and my experience with rebuilding automatics says it's all cleanliness, parts replacement and proper assembly order.

    The output shaft is the last part to come out of the transmission case and the first part to go back in. According to the Novak site, the passenger car TH400s have a very long output shaft which you will need to replace with either the Jeep output shaft or an output shaft from a 4WD Chevy, which I think is the same length and spline count as the Jeep output shaft. If you need to be certain of this in advance, somebody here may know, or maybe ask on a Wagoneer forum like ifsja.org or fsjnetwork.com

    I would just buy any old Chevrolet passenger car TH400, and build a replacement transmission for the Jeepster with the adapter and output shaft from the Jeepster TH400, the case from the Chevy TH400, and whatever old parts I needed from either. Walla, a Jeep TH400 and transfer case with a Chevrolet front pattern, Chevrolet torque convertor and Chevrolet flex plate (if needed).

    Then buy your TDI adapter and run it with your new transmission. Your adapter supplier might have some advice about how to set up the TH400, of which you would have ample opportunity while its on the bench.

    Novak Dana 20 gears page:
    https://www.novak-adapt.com/knowledge/gear-table/

    Novak TH400 page:
    https://www.novak-adapt.com/knowledge/transmissions/automatic/th400/
     
    Last edited: Feb 6, 2022
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  14. Feb 6, 2022
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    This is the factory engine-to-transmission adapter for the Jeepster TH400:

    HydramaticAdapter.png

    This only works with the transmission from the Buick nailhead engine. The nailheads were a 1st-gen Buick engine built in the 50s and early 60s. In some cases Jeep adapted to a BOP engine (225 or 350) but it's not a BOP transmission. Look under your Jeep and you will see the ring adapter, 6.525-1. The Buick does not use the spacer 6.521-1, however it does use its own flex plate and convertor which are unique to the Jeep application.

    Summit and Jeggs sell plate adapters that convert from the BOP pattern to the Chevy pattern. https://www.jegs.com/i/JEGS/555/60172/10002/-1 Possible you could put one of these in there between the Jeep ring adapter, and your TDI adapter. Maybe. Seems quite likely that you'd run into a problem making this work. Plus there is zero aftermarket support for the Jeep flex plate and convertor, AFAIK.
     
    Last edited: Feb 6, 2022
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  15. Feb 6, 2022
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    You can, but it will require an adapter kit. Novak sells this for the 700R4: https://www.novak-adapt.com/catalog/adapters/transmission-to-transfer-case/th700r4-to/kit-107/

    The TH400 is a very strong and durable transmission. As I see it, its main fault is lack of fuel efficiency. The later GM automatic transmissions like the 700R4 will be more efficient and give you an overdrive gear. However, Jeepsters don't typically have deep axle gears like the CJs, and you can buy a lot of gas with the money you'll spend upgrading the transmission.
     
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  16. Feb 6, 2022
    ANTHONY DRANE

    ANTHONY DRANE New Member

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    I would just buy any old Chevrolet passenger car TH400, and build a replacement transmission for the Jeepster with the adapter and output shaft from the Jeepster TH400, the case from the Chevy TH400, and whatever old parts I needed from either. Walla, a Jeep TH400 and transfer case with a Chevrolet front pattern, Chevrolet torque convertor and Chevrolet flex plate (if needed).
    This is where my head is at too and what I meant by using "another GM trans". I was hoping I could use my tail shaft and housing on a trans that was adapter friendly. Sounds like I can. My trans guy will know what I need, being both a GM and Jeep lover.
    I looked everywhere I could think of for a pic of that factory adapter and found nothing. Thanks for the pic. I've been on Novak's site but I thought I had A BOP pattern. I think you can see my frustration. To be honest, I was ready to go this route out of frustration. As with most things I'm discovering that the more I learn, the less I was right about what I thought I knew. I appreciate all the good advice offered from all the posters. We will prevail. :)
     
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  17. Feb 14, 2022
    eyotajeeper

    eyotajeeper Member

    Iron Range
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    a th400 from a 2 wheel drive chevy or gmc truck or suburban, or a passenger car, will bolt up to the adapter that came stock in your jeepster. providing your jeepster had an automatic from the factory. a th350 will NOT bolt up to your stock tc. gm th400 are 32 spline output if irrc, and th350 are 27 spline if irrc.
    The nailhead trans was a th400, and the adapter to the tc was used from the factory in a few different vehicles from jeep. I have used the adapters several times in the past to put gm v-8s into different vehicles.
    Hope this helps.
     
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  18. Feb 16, 2022
    Keys5a

    Keys5a Sponsor

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    Yes, there are numerous GM TH400 bellhousing patterns, BOP, Chevy, and even AMC on the later Jeepsters.
    Something else you need to check on the TH400 is the output shaft spline count and length. The Jeep TH400 had a unique output shaft that mated to the D20 in conjunction with the factory adapter/trans mount. Your original output shaft will need to be swapped over if you use different (Chevy?) case, or buy the Novak or AA adapters to accomplish the same.
    -Donny
     
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