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I need HELP (Doubler)

Discussion in 'OffRoad Design' started by shevygi, Apr 24, 2004.

  1. shevygi

    shevygi Registered Member

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    I have a th475 /forums/images/graemlins/woot.gif(th400)that is new and don't want tear into and void the warranty.
    I want to put a doubler in but I'm not sure what adapter and np203 I need. /forums/images/graemlins/dunno.gif /forums/images/graemlins/confused.gif /forums/images/graemlins/dunno.gif ?????


    Please help.
     
  2. boz42

    boz42 1/2 ton status GMOTM Winner

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    the easiest way is to get a T-400 version 203. u will also need the 203 adapter & the t-400 tailshaft for this combo. after u aquire all that all u will need to do is swap tailshafts in the t-400 and buy the doubler.
     
  3. shevygi

    shevygi Registered Member

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    This is a new tranny that still has /forums/images/graemlins/thumb.gifwarranty /forums/images/graemlins/thumb.gifthat I don't
    want to void. /forums/images/graemlins/confused.gif /forums/images/graemlins/dunno.gif
    whats the diff anyway? /forums/images/graemlins/confused.gif
     
  4. jac6695

    jac6695 1/2 ton status

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    Hey, sorry I didn't get back to you in the other post. I forgot about it. Look around on the ORD site. Lots of good info there. Any TH400 version 203 will work for you (like mine) and you need to seperate the range box (for the first low and high range). The 205 you already have is the only one you need for a Gen2 Doubler.

    The main difference between Gen1 and Gen2 Doublers are the Gen1 uses the factory adapters for the second case where as the Gen2 has the adapter "built in", making the overall setup shorter and somewhat stronger. I believe you can only use your 32 spline 205 for the Gen2, with the Gen1 a 10 spline (4 speed), 27 spline (TH350), or the 32 spline could be used in GM applications. I may have some of this info mixed up, but I am sure Stephen or someone else can correct me.

    So basically, buy my 203 /forums/images/graemlins/whistling.gif, buy the Doubler and have fun putting it all together/forums/images/graemlins/thumb.gif
     
  5. shevygi

    shevygi Registered Member

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    I'm thinking about it.
     
  6. Stephen

    Stephen 1/2 ton status Moderator Vendor

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    The big question is what output shaft do you have? You can measure how far it sticks out of the case and figure it out from there. Use this from our page to help:
    GM TH400 Automatic Transmission:
    If you have a TH400, there are three options for mating the 203 to your trans.

    1: Use a factory configuration. The TH400 was available with the NP203 in heavier duty trucks (3/4 and 1-ton generally) in approximately '78-'79. The factory configuration uses a 1 3/8" stickout 32 spline shaft in the TH400, a 32 spline input gear in the NP203 and a 1.1" adapter plate between the two, somewhat similar to the TH350 adapter plate. This is the shortest way to mate the TH400 and NP203.

    2: Use a TH400 that originally had an NP208 mated to it. This TH400 uses a 32 spline shaft that sticks out of the case about 2.5" and has an adapter housing that's about 2.5" thick. You'll use a TH400 version 32 spline input gear in the NP203 and re-drill and tap the face of the NP203 with the round bolt pattern to match up to the NP208 adapter housing. Benefits of this kit are the parts are quite common since the NP208 was very widely used with TH400 trannies. The drawback is the adapter is about 1.5" longer than the shorter factory configuration.

    3: Use a TH400 that originally had a NP205 behind it. This TH400 uses a 32 spline shaft that sticks out about 4.5". You'll need to use a factory TH400 to round pattern NP205 adapter housing that is 4" thick and once again, re-drill the front face of the NP203 to match the round pattern. The input gear will be the TH400 version NP203 32 spline input. Drawbacks to this system are the overall length with the 4" housing between the two and the expense of buying the factory housing. They're not common as used parts and typically must be purchased new. ORD can supply this adapter.

    If you need more, let us know.
     

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