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th400 tailshaft length?

Discussion in '1973-1991 K5 | Suburban | Truck' started by Bross82, Jan 24, 2003.

  1. Bross82

    Bross82 1/2 ton status

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    hey, i have a 305, th700r4, np208, and 10 bolts.... i'm just curious if the th400 would bolt right up and what tailshaft length is needed? also, what do you think of the remanufactured ones from the summit catalogue, are these any good? how would this transmission hold up with this setup, and the 10 bolts probably have 3.08's in them and i have 35'' tires....i know heat is more an issue with the th700r4. i had hoped to have better axles with lower gears by now, but thats another issue because of money spent on body rot issues.

    thanks for any input,
    matt
     
  2. R72K5

    R72K5 Banned

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    no, al 4x4 tailshafts are same for each model of tranny, th400 is oddball spline count i think 32 ?,

    manual trans are 10 bolt, and 700r4 and th350 are 27 spline, gonna take a different adaptor at the minimum, a th350 will replace that 700r4 ALOT easier
     
  3. Bross82

    Bross82 1/2 ton status

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    i didnt know about the tailshaft length, i just saw in the summit mag it said you needed to specify the length. what do you think of the rebuilt th350 and th400 trannies from summit and TCI? is there a better place to get good already rebuilt trannies at a low price?

    how much more difficult would it be to replace with a th400? in the long run, hopefully only 2-3 years, i plan on swapping in a 454 and adding as much power as possible. so i'm trying to keep that in mind. what adapter(s) would be needed for a th350 and what would be needed for a th400? is there anything else i need to keep in mind that would need to be upgraded or changed such as the torque converter?

    how well will one of the th350 or th400 trannies hold up with: 305/th700r4/np208/3.08 ? dont plan on this being a long-term setup, but the current axles and gears may need to stay in up to a year.

    thanks for any help,
    matt
     
  4. u2slow

    u2slow 1/2 ton status

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    You would be better to find a complete TH400 with a t-case already attached. There's at least three different output shaft lengths all mated to different t-cases. Here's a snippet for ORD's website that outlines this:

    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.
     

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