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700r4 to a turbo 350?

Discussion in 'Chevy Truck Talk & GM News' started by lifted71, Dec 30, 2011.

  1. lifted71

    lifted71 New Member

    I have a chevy 1985 4x4 custum deluxe and there was a 700r4 in it and i want to put a turbo 350 in it would it match up? would i need a new drive shaft and a block?
  2. tbplus10

    tbplus10 Super Moderator Staff Member Platinum Contributor 1000 Posts

    This swap is possible, most go the other way TH350 to 700R4.
    Driveshaft length needs to be adjusted.
    Shift linkage will need to be corrected, I recommend getting an aftermarket floorshifter it makes the swap easier.
    Speedo needs to be corrected.
    Kickdown linkage adjusted.

    Block?
  3. dedmon27

    dedmon27 New Member

    I believe the 700 is a stronger tranny than the 350, I believe the 700 is like a 400 but the 700 needs computer to operate. But a 350 should bolt up as long as you get one made for a 4x4. I believe the 350 shifts off of engine vacumn. So getting it to work in place of the 700 might be tricky. Hopefully a transmission mechanic on here can help. Good luck
  4. Texxxan

    Texxxan New Member

    Stick with the 700R4. Just my 2 cents.
  5. tbplus10

    tbplus10 Super Moderator Staff Member Platinum Contributor 1000 Posts

    In factory form the TH350 is a better trans than a 700R4, holds up to abuse better, early model 700R4's can be modified/rebuilt to be just as reliable as a TH350, but the 700R4 can never be accused of being almost as strong as a TH400.
    Both transmissions use vacuum.
    Depending on what model 700R4 you use it doesnt require a computer, later model 700R4's use some computer inputs but these can be bypassed with a little work. Full computerized transmissions requiring a computer werent in use untill the 4LE series.
    Yes you will require a short shaft transmission unless you want to go with a divorced transfer case, which wouldnt make any sense, it'd be way to much work, it would probably be best to buy a transmission and transfer case together since the adaptor for a TH350 to your transfer case will more than likely be expensive, dont know what transfer case you have though so we cant be a 100% positive on this.
    When its all said and done you'd be better off putting a good rebuild into your 700R4.
    With the TH350 your transmission gear ratios will change and affect MPG.

    I posted this a few months ago, maybe it'll help you in your transmission decision:
    700R4
    1st gear 2nd gear 3rd gear O/D
    3.06:1 1.63:1 1:1 0.70:1

    Turbo 350
    1st gear 2nd gear 3rd gear O/D
    2.52:1 1.52:1 1:1 none

    Turbo 400
    1st gear 2nd gear 3rd gear O/D
    2.48:1 1.48:1 1:1 none

    The 700R4 has a deeper 1st gear than either TH350 or TH400, and the final drive is taller for better cruising RPMs, especially if your running taller than factory tires. You dont state the initial reason for wanting to go with a TH350 so I'm guessing since your truck is 4x4 you plan on running larger tires, at some point you'll need to change axle gearing, my recommendation would be a quality rebuild, larger pan, fluid cooler, and change to friendlier diff gears.
    This is a tried and true combination that thousands of mid Chevy 4x4's are running with little or no problems, really depending on how their treated i.e. maintenance and a throttle happy driver.

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