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Making a 2wd TH400 fit in a 4wd, ??????? Does it swap in ???

Discussion in 'The Garage' started by uglychevyZZ4, Jan 17, 2003.

  1. uglychevyZZ4

    uglychevyZZ4 3/4 ton status

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    i have a np205 abd sm465, i wanna swap in a TH400, and have access maybe to a 2wd one. will / can it work ? /forums/images/graemlins/confused.gif
     
  2. y5mgisi

    y5mgisi 1 ton status

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    The tranie will work but you'll have to swap out the 2x4 out put shaft to a 4x4 one. thats it.
     
  3. 79Beast

    79Beast 1/2 ton status

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    2 & 4 wheel drive TH 400's have different output shafts. If you don't mind changing the output and possibly the mainshaft, then all you need will be the correct adapter and the correct version of the NP205.
     
  4. uglychevyZZ4

    uglychevyZZ4 3/4 ton status

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    ok, how do i know if i have the " right one " since it wasnt made to bolt to a np205?
     
  5. 79Beast

    79Beast 1/2 ton status

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    Almost all SM 465's had 10 spline outputs with 10 spline 205's. TH 400's had 32 spline output with 32 spline 205's. If you want the auto, find a complete tranny, adapter, and Tcase.
     
  6. uglychevyZZ4

    uglychevyZZ4 3/4 ton status

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    so to swap in the 2wd 400 whats need to do to get it mated with my 205 though? once the shaft is changed will it bolt up or is a adapter plate needed?
     
  7. Longhorn4x4

    Longhorn4x4 Registered Member

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    First off, you'll need the correct output shaft for the transmission. The problem here is there are two different shafts, depending on your adapter and input shaft. Another problem is the case is slightly different. The 4x4 case has a thick flange where the dust cover bolts on, that has six BOLT (not screw) holes. The dust cover is different, it is thick aluminum, and has bolt bosses to attach strut rods that run from the motor mounts to the dust cover. The reason for that stuff is to keep the bellhousing from breaking due to the load of the transfer case on the back.

    If you don't have the correct case, make certain ALL of your mounts are good, preferrably urethane, and that you use the long bar from the side of the case to the bellhousing bolt, and the mount on the side of the case that goes to the frame.

    Now we come to the transfer case. The problem here is that the case itself is wrong for the 400. The 400 input shaft has a bigger bearing. You must acquire the input shaft and the bearing, tear the case down completely, have the hole in the case bored out, and then put it back together, with the new shaft and bearing. Now you need the correct adapter plate for the input shaft for the case and output shaft for the transmission, no shaft adapter is needed. Be prepared to spend $1K. At least.
     
  8. nvrenuf

    nvrenuf NONE shall pass! Premium Member

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    There are different tailshafts offered in the 400 but it's not necessarily a 2wd / 4wd thing. You can get a 2wd version that will have the right tailshaft for a 205, I got one froma 2wd motorhome with a bolt on rear yoke that went right on to my 205 (I already had the correct 205).

    The 205 t-cases prior to 85 were 10 spline BUT from 85 on they used the same female 32 spline input shaft as the 400 version 205 of the same year span.

    If your 205 is a 10 spline cse you can change the input shaft to a 400 style. There is a different size bearing so you will either have to bore the face of the t-case or buy a bearing with the correct inner / outer diameters (seen it done).

    Any way you go you will need to find the correct adapter, that wont be cheap.
     
  9. nvrenuf

    nvrenuf NONE shall pass! Premium Member

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    I forgot, check out the ORD web site it has really good info and pics concerning the 205 input shafts.
     
  10. 77fixer

    77fixer 1/2 ton status

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    I used the 2wd 400. It had the short tailcone which had an output shaft that stuck out 4.5" from the rear flange of the trans. It used a bolt-on yoke but the splines matched the 32 spline 205 input. You need the correct adapter, input shaft and bearing, then get the 205 case bored to fit the larger bearing.

    Brett /forums/images/graemlins/burb.gif
     
  11. JK5

    JK5 1/2 ton status GMOTM Winner

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    Sure it will work....but the belhousings are weaker on the 2wd!!!! /forums/images/graemlins/eek.gif
    [​IMG]
    Here's the 4wd....check-out the inspection cover area...its pretty thick!!!!

    Now check-out the 2wd
    [​IMG]

    It's alot thinner in that area....

    I'm using mine for parts.... /forums/images/graemlins/pimp1.gif
     
  12. nvrenuf

    nvrenuf NONE shall pass! Premium Member

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    Interesting trivia...

    The HD case that you have pictured could have come in a 2wd. Somewhere in the late 80's GM stopped producing the light duty car type case and exclusively used the HD style case. Just look closely at the later stuff with out the O/D option, after the TH350 was discontinued the TH400 was the only 3 spd available.

    It will have the bosses cast into the case for the HD cover but it will have a tin or plastic car type cover on it. You can drill the case and use nuts & bolts or tap it like GM would have.

    I have 3 cases like this. A great source for these is an Astro van. /forums/images/graemlins/cool.gif
     
  13. 77fixer

    77fixer 1/2 ton status

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    They put TH400's in Astros?!! /forums/images/graemlins/shocked.gif

    Brett /forums/images/graemlins/burb.gif
     
  14. JK5

    JK5 1/2 ton status GMOTM Winner

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    Cool....
    Thanks for the info....
     
  15. nvrenuf

    nvrenuf NONE shall pass! Premium Member

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    It sounds crazy but they did. Like I said, after a certain point the TH400 was the only 3spd auto in production. A couple of the ones I have came from Astro's with a 4.3 V6 (needless to say this was a huge suprise the first time I saw one! /forums/images/graemlins/eek.gif).
     
  16. nvrenuf

    nvrenuf NONE shall pass! Premium Member

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    Sorry, allow me to clarify my trivia...

    The vans and such are great sources for the HD cases but the trannys in a lot of these vehicles are TH375's (basically a TH400 case with a 27 spline tailshaft). Things like the small motorhomes and such are a good source for the true TH400 or TH475 with the 32 spline tailshafts (but you will still need to double check the tailshaft length).

    Basically, the big red flag for finding an HD case is a later vehicle without the O/D option.

    Sorry for any confusion. /forums/images/graemlins/crazy.gif
     
  17. Seventy4Blazer

    Seventy4Blazer 3/4 ton status

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    everybody is looking at this as the glas is half empty. this would be a GREAT thing in my eyes.
    i would call around and find out how much a divorced input is on a 205 and if it is a direct swap into your case.
    thats how i would do it. divorced case is cool. you can make it so your drive shafts are identical in length. no vibes up front and still a good angle out back.
    Grant
     

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