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Need Help... swapping in a 700r for a th350 - what trouble may i run into?

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by ak7, Aug 15, 2002.

  1. ak7

    ak7 Registered Member

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    I'm running a th350 with 205 tcase and a stock 350 motor in my 172 GMC Jimmy. I've got a 700r sitting on the side of my house just waiting to be put to use. What trouble will I run into with the swap? Can I use the same tranny frame brace as the th350? I'm not one to like extra holes anywhere in my frame or body so I'm going for a stock finish look on this project. Any helpful tips would be appreciated. I don't know if this might help but the 700r was pulled from an 85' Suburban.

    Ak7
     
  2. BARRAZA

    BARRAZA 1/2 ton status

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    It's a good swap but there are a lot of details to consider. A 700 is longer than your 350 so something has to move, most people move the transfer case back but that will require new driveshafts. I have measured mine and think I will move the engine forward when I go to a 700, that way the transfer case shifter will not move back toward the seat and no driveshaft mods required, but you may have oil pan / axle clearance problems if you have no lift(fill out your profile). The 700 will also need some adapting to mate with your 205, it will bolt to the 350 adapter but will need a new output shaft (Advance Adapters has them) or use the stock output shaft with a spacer between the 700 and the 205/350 adapter. There was the part number for the spacer in a post recently, do a search. Also, if the 700 you have has not been updated, it should be before you do the swap. There were major updates to 700's made in the late 80's, I think it was 86. The OD in a 700 will be a lot of gear to pull if you have stock type ratios, even if you only have 31's you will need 3.73 gears or preferably 4.11's.
     
  3. ak7

    ak7 Registered Member

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    Thanks for the good info. I was thinking about moving the motor forward a bit. A buddy of mine swapped in a 700r for his 67 RS Camaro. He decided to move the motor forward . To do that, he had custom motor mounts welded to push the motor about 3/4" forward. That allowed him to use a 400 tranny mount with the stock mount holes in the frame. I was hoping to do something like that. I guess the motor mount cross member could be moved forward as well. Decisions... Decisions... Moving the motor forward would also makes some more room for hte HEI.

    Ak7
     
  4. Chris_T

    Chris_T 1/2 ton status

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    I did this and moved back the crossmember .. I believe it is 1 3/4", but don't quote me on that. I was getting a new fronst shaft anyway. If you have a reasonable lift, or are planning to do so in the next little while, that might save you from a new rear shaft. Otherwise the swap is as easy as it gets. I'd go with the new tailshaft for reliability, but that's just me. PM me if you have any questions
     
  5. jmeador74

    jmeador74 1/2 ton status

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    Hey... its been a long time since I have posted to this forum...I have taken a long vacation from this website since my move from Texas to the Wash. DC area... well let me tell you how I did my swapover...

    I had a 327/465/205 and now am at 400/700r4/205... and this is what I had to do to get there... I measured both lengths of trannies and the 465 came out to be 25" long and the 700r came out to be 27" long... so I made the decision to go ahead and move my engine forward 2 inches on the frame rails by sliding the engine crossmember forward two inches and drilling new holes. what I had to do to make the forward move complete was stretch the throttle cable forward a bit and cut the fan shroud down and cut a short length of fuel line out... I also had to replace the bracket holding the throttle cable on the engine block... and then had to extend the exhaust 2" and the way I did that (temporarily) was by using 4 exhaust clamps and two adapter sleeves to lengthen the exhaust pipes I just cut the exhaust pipes somewhere where it was straight and then put the adapter sleeves in place measuring a two inch space and then clamped it off. The clamps and sleeves were bought from any auto part store in the exhaust muffler section...

    Now for the other info... the tranny I have (700-r4) is a completely rebuilt tranny with all new stuff and shorter shaft to fit the 205 without having to use the spacer adater. Also the tranny I have no longer requires the use of a computer, so I don't have that thing to mess with.

    I do recommend going for the short shaft. and just moving the engine forward two inches. if you opt to stay with the long shaft and add the spacer that is going to add two more inches to your drive line not to mention the 2 inches already added for the length of the tranny for a possible total of four inches. Just more trouble for your driveline with incresed drive angles and having to moved the stickshifts around. I've been able to keep most of my stock locations on everything I think...
     
  6. topjimmy

    topjimmy Registered Member

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    Hey, I'm from Glen Burnie, MD...have a 71 Jimmy with 4" lift, and 35's, too! Gimme a shout...later. /forums/images/graemlins/k5.gif /forums/images/graemlins/thumb.gif /forums/images/graemlins/usaflag.gif
     
  7. ntaj*ep

    ntaj*ep 1/2 ton status

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    I did this in my 72 I moved the cross member and T-case mount back about an inch, I used AA output shaft for the 205 t-case. If you would like guidence PM me. /forums/images/graemlins/thumb.gif
     

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