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700R4 to TH400 swap???

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by MNorby, Jun 4, 2002.

  1. MNorby

    MNorby 3/4 ton status Premium Member GMOTM Winner

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    Well, blew up the 700R4 again last Saturday. I still owe $300 on fixing it last time. Anyhow, the shop said I can get an exchange 700 for $680. Well, went to the salvage yard and for $700 I can get a TH400 with a NP 241 that are both newly rebuilt. The yard will give me $200 for my old tranny/ t-case but I think I can sell it for more since the t-case is rebuilt and the tranny has a new pump and converter and lockup silinoid. I think I will get the TH400/NP241 but jsut quirious if anyone knows what mods will be needed to do that swap. Any vacuum line difs to shift compared to the TV cable for the 700? Crossmember bolting up? driveline lengths? Cooler lines? Shift linkages? etc.... Thanks /forums/images/icons/smile.gif
     
  2. ken

    ken 1/2 ton status

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    I did this very swap to my wife's '90 Suburban after blowing up 6 700r4s over a period of 5 years. Your same crossmember will work and no driveshaft mods need to be made. One thing I do remember is that the dipstick tube will need to be from the 400 trans, as the 700s will not work. Also, I ran a vacuum hose down from the back of the intake manifold to the 400's vacuum modulator. You can get a kickdown switch for the 400; it mounts under the accelerator pedal, unlike the 700's cable type kickdown system (also like a TH350 tranny). I never did get the kickdown switch...I could put in one if I want to though, as 400s were an option in 1990 and the accel pedal bracketry has a place for a kickdown switch. This is one of the best upgrades you can do to prevent future tranny failures. Some on this board are having marvelous luck with their 700s, but me, and it sounds like you too, have not, therefore the need for indestructibility in a transmission...the TH400. Good luck with your swap, you'll be happy knowing your tranny failure days are OVER!!
     
  3. MNorby

    MNorby 3/4 ton status Premium Member GMOTM Winner

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    hey, thanks. Ya, this is the 4th time this 700 has died somehow or anyother. I am getting the TH400/NP241 from a 1990 'burban. I'll see if I can steal the braketry too
     
  4. ken

    ken 1/2 ton status

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    Also, cooler lines are the same, bolted right up. Transfer case linkage was the same, I did not change it at all, or even have to adjust it. Shift linkage to the trans was the same, bolted right up, except now there are only 3 detents for gears instead of 4 with the 700...so the gear pointer in your dash will be off, I solved this by going to a wrecking yard and getting a gear selector/pointer assembly from a truck with a 3 speed auto tranny, rather than a 4 speed auto. Bolted right in and now shows the correct gear. No problem!!
     
  5. ftn96

    ftn96 1/2 ton status

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    Ok, Sounds like a plan. HOWEVER!! It has been my eperience, that if your tranny goes....little metal shaving go flowing throughtout the tranny and they end up flowing through what? The Torque Convertor. Now, unless you can guarantee you can get "ALL" the metal shaving, chunks, nicks whatever out of the TC, then you SHOULD/BETTER replace it. So if I were buying the 700 from you, The New TC wouldn't add squat to the price. Just my 2 pennies. Good luck with the swap over.
     
  6. MNorby

    MNorby 3/4 ton status Premium Member GMOTM Winner

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    Well, got the 400 in teh truck just gotta hook up cooler lines and fill her up. I don't have the gas pedal kick down yet, will it hurt anything to run without it? The new tranny tcase is all brand new basically and paid 700 for it minus 200 for my old tranny tcase
     
  7. MNorby

    MNorby 3/4 ton status Premium Member GMOTM Winner

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    also the speedo for the new 241 is electric and the old 208 was mechical. Is there an adaptor to go from electrical to mechanical?
     
  8. ken

    ken 1/2 ton status

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    Running without the kickdown is no problem. I still haven't put mine in and it's been 2 years!! Just if you're in a situation where you're bogging down in third gear, manually pull it down into second to save wear and tear on the tranny.
     
  9. BlazerGuy

    BlazerGuy 3/4 ton status

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    Would this swap be any different in a K5 with a NP208, assuming I have the correct adapter for the t-case. I want to know because when my 700 goes out I will promptly install a 400. Do it once, do it right......
     
  10. dawson444

    dawson444 1/2 ton status

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    Its the same. I have done it.
     

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