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transmission swap

Discussion in 'The Garage' started by narnar, Mar 31, 2004.

  1. narnar

    narnar Newbie

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    I have a 77 blazer with a turbo 350 and 203. I recently lost all of the forward gears in that transmission. I have acquired a turbo 400 with a 208 transfercase that is in good shape out of a early 80s 3/4 ton and i can get the front driveshaft easily. What do i need to do to make the rear driveshaft work and will my old crossmember work because i dont have a new one. Is this swap worth the hassle or should i just rebuild the turbo 350. I am on a very tight budget also because i am in high school and dont currently have a job. Thank you and forgive me if i didnt give enough info because this is my first post.
     
  2. bablazer73

    bablazer73 1/2 ton status

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    First think you should do is fill out your profile!! We like that!
    I could help you, if your close. The crossmember will not work. You will need the later crossmember. which i have. Your old rear shaft has the slip part in the shaft, and the newer style has the slip going into the t-case. This will require a rear shaft, I think I have. If you don't have the shifter for the 208, then thats something else you will need. Which i also have. so, unless you have, or can get these parts, It might just be easier to have the 350 rebuilt.

    Where are you located??
     
  3. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    if the 400/208 has the short adapter you will need a new crossmember but if it is the tall adapter you will not need a nem member. you many need to redrill the frame though.
     
  4. grd2go

    grd2go Registered Member

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    You are going to need other parts off the tk that the 400 / 208 come out of like the rear driveshaft then it needs to be shortened you need the shifter assembly from the tk the kickdown for the 400 trany is diferent the crossmember is different you might need a conversion joint to mount the driveshaft to that old of a axle if the donor shaft came from the mid 80s the th-400 is longer than the 350 so you need to make sure the exhaust dosnt need a little working over too then you have a 208 with a slip yoke on the rear that is prone to eating seals and leaking besides that its a decent transfercase but at the same time the 203 is heavy but just as strong if not stronger than the 208.. You come to money thing a new rear shaft $200-$300. Used crossmember $25-$75 at the junkyard plust the shifter and kickdown parts at least another 50-$100 so all said in done what will youre local tranny shop bench a TH-350 for I can get it for $400-$450 were I live. Used 350 here are 100 to 150 dollars a used or rebuilt TH350 bolts right back in no hassels and you can do it in a day... If you dont have the parts I wouldnt try it because murphys law says what can go wrong will go wrong /forums/images/graemlins/whistling.gif /forums/images/graemlins/crewcab.gif
     
  5. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    whats different in the crossmember?
    ive never seen other than 3 crossmembers, flat, w shaped and s shaped.
     
  6. narnar

    narnar Newbie

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    thank you for your replies. It is kind of sounding like it would be better to rebuild the 350. I have done some research and i think i am capable of something like this. What kits would be a good choice that are fairly inexpensive I don't necesarily need a race transmission but a mild shift kit would be nice any recomendations. Also if i were to find a used 350 would it have had to have been attached to a 203 or would different ones work?
     

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