Register now to get rid of these ads!

thm400 transmission 4x4 vs 2wd

Discussion in 'The Hokey Ass Message Board' started by v8nova64, Jun 22, 2012.

  1. v8nova64
    Joined: Jun 4, 2011
    Posts: 134

    v8nova64
    Member
    from !!

  2. squirrel
    Joined: Sep 23, 2004
    Posts: 46,718

    squirrel
    Member

    Yeah, that's about the size of it.
     
  3. v8nova64
    Joined: Jun 4, 2011
    Posts: 134

    v8nova64
    Member
    from !!

    I notice that there are a few different write ups for different mods in this writeup. I think i can do all of them. I think it will be a wesome to be able to hold any gear like a manual trans without the transmission up or down shifting on you. Then on the street i can just throw it in drive and let it do the shifting.
     
  4. 12bjoshu
    Joined: Nov 6, 2011
    Posts: 17

    12bjoshu
    Member
    from Kansas

    I don't know if anyone has mentioned this yet, and I don't really feel like wading through the comments that are really repetitive. In 78, they started with the K-case transmissions. These got put into the 4x4 trucks, and from what I understand, heavy duty operations like cop cars. These cases are thicker around the bellhousing, and by the tailshaft section. The reason behind this is the guys running the trucks would get hung up and hammer on the truck and the transmission would break in these areas. So, the trannies got made heavier-duty for these applications. Being out of a 79, this should be a K-case 400. The simplest way to tell is where the dust cover bolts up. If it has 6 bolt holes versus the regular 4, then it is a K-case. I have over 60 of the OT style 73-87 trucks, and know this for a fact.
     
  5. v8nova64
    Joined: Jun 4, 2011
    Posts: 134

    v8nova64
    Member
    from !!

    would this trans need a transfer case if so it wont work unless i convert it to 2wd. What length tailshaft did these transmissions have?
     
  6. Probably the best thing for you to do is go to the library and loan the Ron Sessions book. Read it cover to cover.
    THEN start your search.

    Cosmo
     
  7. 12bjoshu
    Joined: Nov 6, 2011
    Posts: 17

    12bjoshu
    Member
    from Kansas

    I am fairly certain that these transmissions will work without a transfer case. While I have not tried this personally yet, the reason I am fairly certain is because they used them in police cars also, which would have had just tailshafts and housings. Also, the transmissions still had the 6 bolt pattern the same as regular cases. I believe the length varied between whether the transmission was mated to a NP203, NP205, or an NP208. Also, for racing purposes, the K-case is a highly regarded transmission around here, because of the strength factor over the regular case.
     
  8. squirrel
    Joined: Sep 23, 2004
    Posts: 46,718

    squirrel
    Member

    The 6 bolt cover is nice, but not really necessary for most hot rod uses.

    The 208 was first used in 1981 as best I can remember, and as far as I know it's the only one that might have a long enough shaft to use with a tailhousing...but there's no where to put a speedo gear on that shaft.
     
  9. F&J
    Joined: Apr 5, 2007
    Posts: 13,217

    F&J
    Member

    Here is what I did, when converting a 79 GMC TH400 2wd trans to a NP205 transfer case.

    Sure, the GM parts book says the output shafts are not the same, and that is true....but, after pulling the entire trans apart to swap in the new output from GM, the differences were not an issue for my swap.

    There were differences in snap ring grooves that were not needed. The 2wd output was a bolt-on yoke with a threaded hole at the end, and the 4wd shaft does not.

    So, I returned the new shaft to my friend at GM for refund, and put it all together as it was, except I did new seals/clutches while it was apart. Did this in 82 or 83, that truck went 11 years before rotting away, and now that same trans is in my 66K20 still pulling overloads whenever it leaves the garage.

    So, that is the opposite swap you are doing, but if a slip yoke will fit it, it should work, I would think.
     
  10. Crosley
    Joined: Mar 3, 2001
    Posts: 1,035

    Crosley
    Member
    from Aridzona

    GM used 3 different length T-400 out put shafts for 4x4 application. All were 32 spline

    In an early 205 t-case, the 4x4 shaft was the same length as the short 2wd shaft. The adapter from t-case to the trans was fairly long

    When the 208 t-case was introduced, the shaft for it was shorter and the 205 adapter was changed so the 208 and late 205 used the same shorter shaft.. the t-case adapter was shortened for the 205.

    The 203 t-case uses the shortest output shaft from the T-400. These are getting hard to find.
     
  11. v8nova64
    Joined: Jun 4, 2011
    Posts: 134

    v8nova64
    Member
    from !!

    in what vehicles could i find a 2wd with 4" tailshaft. the 4" tailshaft would be perfect with my driveshaft length all i need to do is change the yoke to 32 spline
     

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2020 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.