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2wd Th400

Discussion in 'The Garage' started by fireplug, Dec 14, 2005.

  1. fireplug

    fireplug 1/2 ton status

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    Well I just picked up my first K5. It's a '76 350/350/205 D44/14bff both locked.

    I've searched and read recent posts on the subject but there seems to be a lot of conflicting info.

    I currently am running a 350/350/205 and really want to replace the tranny with a rebuilt 2WD TH400 that I have sitting around. Can I make this work?

    I am also thinking about doing the doubler with a 203 in the future (or now if it makes more sense) if this makes a difference.

    What considerations or other requirements should I consider with this buildup?

    Thanks for any help guys.
     
    Last edited: Dec 15, 2005
  2. jekbrown

    jekbrown I am CK5 Premium Member GMOTM Winner Author

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    congrats, and welcome to CK5. :thumb:

    2wd trannys have yoke outputs... it would probably be a royal PITA to swap over the 4wd stuff to make your th400 4wd-output-capable. Parts alone would probably cost as much as a core 4x4 th400.

    If you are ever going to "go doubler" it makes sense to do it at the begining... that way you won't have to get your driveshafts resized more than once... and you can build your drivetrain just once.

    What type of terrain you plan on running and what size tires. A doubler + locker + D44 could = exploded D44 parts... depends on your right foot and expected use of the rig though. Post what tires you want and what terrain you'll be in and people can offer specific advice appropriate to you and your rig.

    j
     
  3. fireplug

    fireplug 1/2 ton status

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    If the Th400 wasn't freshly rebuilt and free I wouldn't be so hot to do it, but I can't help but think I'll still make out ok $ wise in the end.

    The big question though is how it actually is done. Some guys are saying it's simply a matter of unbolting the tailshaft that would be alright!

    The 350/205 combo is from a '76 and the 2WD TH400 is from a '79

    The locker in the front is actually an Electrac (at least I think) it is a posi until switched on. I'm running mud trails mostly, not rocks like you guys call rocks, but muddy slippery stuff. I would use the locker with discretion for sure.

    Tires will be either the 36.5 Super swampers that came with it or my 37" Trxus off my Burb.
     
  4. fireplug

    fireplug 1/2 ton status

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    ttt anyone, anyone? I could really use your help guys! If no one has any first hand knowledge could you point me in the right direction for info?
     
  5. gmtech954

    gmtech954 Registered Member

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    the output shaft on the 400 will not fit into the input of your t case. the sizes and spline count is wrong.
     
  6. big4x4ride

    big4x4ride 1/2 ton status

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    th400 32 spline output th350 27 spline output
     
  7. k20

    k20 3/4 ton status

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    Yeh wont work with your tcase, but the way I understand it, unbolt the tailshaft and its ready to rock.
     
  8. fireplug

    fireplug 1/2 ton status

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    Soooo what you are saying is unbolt the tailshaft and it will work as long as I'm using a TH400 205 case?

    Thanks for the help so far.

    Oh and if I'm doing the doubler with the 203 is it the 203 that I need to match the TH400 to? Sorry I'm dumb.
     
  9. rdn2blazer

    rdn2blazer 1 ton status Premium Member

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    there was an article in Petersons 4 Wheel about this. it showed all the differences of the two. did not recomend it.
     
  10. jekbrown

    jekbrown I am CK5 Premium Member GMOTM Winner Author

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    yes, you'll need a factory th400-version np203 and the factory adapter along with it. There are 3-4 different length th400 outputs chevy used over the years... for the 203 it used a very short stubby output shaft. To keep the driveline length sane a lot of people like to use the short output 400/203. The adapter for this combo is only 1.1" thick and as I said, the shafts is short... so its pretty much the shortest way to do a doubler. That is the combo I am using for my K5. Basically you need a factory th400/203 combo... a doubler adapter and a np205. Most people go with a th400-version np205 because its 32-spline input is hella beefy... but there are some doubler-makers who will offer a 27 spline intermediate shaft that allows the use of a 205 that came from the factory behind a th350 (much more common and cheaper). To each their own... I'd rather have 32-spline shafts from the trans all the way to the driveshafts... but thats just me. ORDs web site has all the tech info on what years have what outputs etc. Poke around their site for more details.

    j
     
  11. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Jek is correct. All th400 4x4 outputs are 32 spline, and th350s are 27. th350 has the same output for 203 and 205, not sure about others. th400 has different lengths for each of the 203, 205, and 208, and none of these is the same as a 2WD. The tail bolt pattern on a th400 is 6 bolt, th350 is 4 bolt, so obviously, even if the output shaft length were the same, they would not interchange. Furthermore, there is a round and "figure 8" 205 adapter (this is the bolt patter on the tcase side).

    This is one place Ford kick GM's collective butt. All Fords use the same round pattern adapter and use the far superior 31 spline large bearing, short female input (which is comparable to the short 32 spline used only on th400s by GM). Better design and much easier to mix and match on a Ford in this case, though no other than I'm aware of.
     
  12. thebigdaddyof2

    thebigdaddyof2 1/2 ton status

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    Only one thing to add:
    Not true.
    Many were the slip yoke design.
    I have yet to pull the slip yoke housing off of the 2WD T400 I have
    to measure the output shaft length...
     
  13. blazin_blazer

    blazin_blazer 1/2 ton status

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    th 400 with yokes

    ussually come out of big van trucks like a u-haul or a potato chip delivery truck ...pizza delivery...mid-sized van trucks...never seen 1 in a 1ton down
     
  14. fireplug

    fireplug 1/2 ton status

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    I have to pour over these responses again, and compare them to the other posts too.

    what about replace the shafts? I know this would likely be pricey but If I end up with a bomb proof driveline I gotta wonder if it wouldn't be worth it.

    Otherwise I might have to build up the 350 I have. Hmmmm.

    Oh and I'm going to start searching for adapters, I know advance adapters, where else should I look?
     
  15. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    If your 2WD TH400 has a bolt on yoke then you can remove the tail housing and it is now the same as a 4WD TH400 as far as output length is concerned. A 4WD tranny case is thicker and uses an aluminum cover for the converter which has 6 3/8" bolts holding it on unlike a 2WD case which uses a sheet metal cover with 4 sheet metal screws.
     
  16. blazin_blazer

    blazin_blazer 1/2 ton status

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    th400's

    why not a short tailshaft th400 then ..i have a buddy who has a th400 with the fixed yoke that he had built several years ago and runs it in the derby every year and it looks to be the same as a 2wd short tailshaft th400 i have sitt'n in my shop except for the yoke....is it a spline count thing?
     
  17. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    All TH400's are 32 spline. I think the short version TH400 with a slip yoke still has a longer shaft than the bolt on yoke style does but not 100% certain so don't take my word for it.
     
  18. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Which 4WD th400? I don't think it's the same as any of them, but that's just a vague opinion since I don't recall where I hear/read that. However, I am certain that it is not the same for more than one, since there are 3 dramatically different 4WD output shaft lengths. Not to mention the bolt on yolk has a threaded end that would need to be cut off since otherwise it would prevent spline engagement. Like I said, if you cut the end off, there might be enough spline to work for one of them, but the 3 lengths are different enough that I fail to see how it could possibly fit more than 1...

    And the 4WD cases are not thicker. In fact, from the bell back, they are identical. And even at the bell, the only diff is the heavier flange with threaded holes for the cast inspection cover. I've actually cut up and mic'd/measured/examined 2 K cases to come to that conclusion, and I suspect it's true for "HD" cases as well.
     
  19. thebigdaddyof2

    thebigdaddyof2 1/2 ton status

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    Exactly!
    The information on the THREE DIFFERENT lengths of output shafts are listed on the Doubler page at ORD. Hell, I've posted the info here several times.
    http://www.offroaddesign.com/catalog/doubler.htm

    On the 4wd T400s, there are THREE DIFFERENT lengths of output shafts to bolt up to three different transfer cases (technically four if you count NP241).

    Like Baddog has proven, the only real difference in the T400 cases is in the ability to bolt up the cast metal convertor cover, instead of the flimsy sheetmetal type. This allows the two "triangulation" bars to be bolted up to help reduce the likelihood of cracked bellhousings.

    When I get a "roundtuit", I will unbolt and remove the short tail housing from the (slipyoke style) 2wd T400 I have and measure the shaft stickout to see if in fact it would work for one of the applications.

    To the original poster:
    Do the research and learn what you need for your setup.
    Then, unbolt the tailhousing from the T400 you have to work with.
    Meausure the shaft stickout length and see if it will match one of the listed applications. You will also need to be concerned about the amount of splines that you are dealing with. Even if the 2wd shaft stickout will work, you may not have enough spline engagement.

    Post up a pic of the output shaft of the 2wd T400 you're working with.
    I have both the 203 and the 205 version T400s that I may dig out and snap a pic of.
     
  20. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Sorry for not stating which 4WD version, but the shortest version is what i'm talking about.

    I'm not sure what you're talking about having to cut a portion of the shaft off. The 2WD TH400 that was used in some trucks and also corvettes is the shortest version TH400 made and the END of the shaft is drilled and tapped for a bolt so that you may bolt the fixed yoke to the end of the shaft. The shaft is still splined all the way to the end just like the rest of them.
     

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