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Need a walkthrough for tranny swappage... **UPDATE**

Discussion in 'The Garage' started by PhoenixZorn, May 26, 2005.

  1. PhoenixZorn

    PhoenixZorn 1/2 ton status

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    I'm doing a tranny swap tomorrown on the Blazer I'm picking up... Removing the TH400 and T-Case, and replacing it with the TH350 and T-Case... I think both T-Cases are NP208s, but I'm not positive... I think I've read that spline counts for both trannys are the same, but as the TH350 already has a T-Case attached, that won't be so much of a problem right? I am guessing that the Driveshaft has a 1310 joint, as it is a 10 bolt axle, and that the T-case will match up perfectly, and I won't have to "Machine" or buy any extra parts...

    I need a quick rundown of the swap, as I've never done one before, but I'll have a full shop to work in, thanks to MISFIT014x4. At a certain point he'll be helping me, but until then, I'll be pretty much on my own, with a little help from my Dad. I also need a list of parts that will likely need to be replaced due to normal wear and tear (and standard replacement due to a swap of this nature.) Thanks in advance guys...
     
    Last edited: May 31, 2005
  2. Chaddy

    Chaddy 1/2 ton status GMOTM Winner

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    trans

    if you already have a 400 then your set!! thats 1 of the best tranny's in the world and i would never swapp it for a turbo 350 regardless of T-case
     
  3. PhoenixZorn

    PhoenixZorn 1/2 ton status

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    The 400 only drives in reverse.... when it has fluid in it... and that leaks out in a few minutes... I'm doing the 350 swap because it was all I could find on short notice.... Unless someone in Wisconsin has a 400 they'd like to deliver to me like right now, I'm going to have to go with the 350
     
  4. az ranger

    az ranger 1/2 ton status

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    If You Must Go With The Th 350 The Spline Count Is Different 32 Spline For The 400 And 27 Spline For The 350 But If You Are Swapping In T-case Too Then It Won't Matter

    As Far As Replacement Parts I Would Either Flush Cooler And Lines Or Replace
     
  5. PhoenixZorn

    PhoenixZorn 1/2 ton status

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    Do all 400s and 35s have coolers?
     
  6. bugspray

    bugspray 1/2 ton status

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    It would be a good time to replace the upper and lower tranny mounts.
     
  7. sweetk30

    sweetk30 professional hooker Premium Member

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    the 400 is longer than 350 also. so drive shafts are diffrent. as listed before 32 spline for 400/ 4l80-e 27 spline for 350 and 700/4l60-e trannys. also the 400/4l80-e is 6 bolt tail housing. 350/700/4l60-e is 4 bolt tail housing. easy swaps but need to swap some stuff around. and dont forget the kick down stuff for the 350 tranny its cable and 400 is switch setup.
     
  8. PhoenixZorn

    PhoenixZorn 1/2 ton status

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    sweetk30... the mounting holes for the 4 bolts should already be there right? Just basically a weaker tranny in the 350 than the 400.... I have a feeling I'm going to be spending more than I thought on this swap...
     
  9. sweetk30

    sweetk30 professional hooker Premium Member

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    4 bolt for what? if tcase crossmember then you will most likly need to drill new ones as th350 setup is shorter. and yes 350 is smaller tranny. but i had one in my 1ton with 38" tires and it was 6500lbs truck no problems for over 3 years . and all that was with built 400 sbc. good tranny in my book. and lower first gear also than 400.
     
  10. PhoenixZorn

    PhoenixZorn 1/2 ton status

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    I'm still in need of a pictured walkthrough of removing and reinstalling the trannies.... I HAD a Chiltons manual, but can't find it anywhere... I'm hoping it wasn't in my burned truck... heh
     
  11. dhcomp

    dhcomp 3/4 ton status Premium Member

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    Um, disconnect/unbolt everything, remove old tranny/tcase, install new one in reverse order?

    Haha, sorry, i have no idea.

    Remember you can get basically the service manual off of autozone.com (not sure if it goes back to those years, but they should have some late 80's stuff that should be similar.
     
  12. az ranger

    az ranger 1/2 ton status

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    1. Place Jack Under Tranny Transfer Combo.
    2. Remove Driveshafts
    3. Unbolt Crossmember.
    4. Unbolt Tranny From Engine (its A Good Idea To Support Engine Somehow So It Dont Push Distributer Etc. Into Fire Wall)

    5.dontforget To Disconnectt All Linkages And Cooling Lines Etc.

    Install In Reverse Order
     
  13. PhoenixZorn

    PhoenixZorn 1/2 ton status

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    Thanks guys... after watching the removal of the 350 from the truck it was on, I think i can pretty much do this with my eyes closed... yeah right... but I have a general understanding of how it's done now...

    The output shaft for the rear driveshaft is a slip joint right? What I mean is that it doesn't need to seat all the way into the t-case to get a spline lock, it's meant to travel a little... am I correct on that assumption?

    Also, I figured I'd have to drill new holes, but here's a mind boggler... I watched the removal from above, as the cab of the donor truck was completely ripped off... All the work was done from on top rather than from underneath... I don't have that luxury when removing the 400 or reinstalling the 350. How shoudl i go about removing the 400 from under the truck and replacing the 350 where it should be? These guys basically dropped the tranny to the ground, then picked up the frame with their makeshift Front End Loader with I-beams for forks.... then we proceeded to put the tranny and t-case in the trunk of my Nissan Stanza... :D :D :D Needless to say, I drive a lowrider now... it's squirrelly at highway speeds too... haha.
     
  14. PhoenixZorn

    PhoenixZorn 1/2 ton status

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    Ok, so it took us 9 hours (including downtime) to just get the tranny and t-case out of the friggen truck... and we had a guy who works on trucks all the time helping us... Anyway, I'll be headed down there again this Saturday to finish the job and hopefully drive the new beast home... it has AC that actually works, but it's R12, so I'll have to get it upgraded if I want to transfer it to my truck...

    If someone has a chance, I need pictures of NP208 and NP205 t-cases... we think... but aren't sure yet... that the t-case we took out of the truck is a 205, as it looks much different than the 208 we are about to put in (for simplicity.)

    Also, I'm planning to cut the fenders while we are there due to the fact that they are beyond rusted out, and when you have the tools, you might as well take advantage of it... anyone have any suggestions on getting opposite sides to match?? i don't want to cut 4 inches on one side and 5 inches on the other...

    Oh yeah... if it is a 205, I'll have it rebuilt "bullet proof" to put on the back end of my 465 when I rebuild my truck...
     
  15. sweetk30

    sweetk30 professional hooker Premium Member

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    if the tcase is all alum then 208 or newer. if all steel cast iron then 205. if steel cast iron with alum back end for driveshaft its 203.
     

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