wanting to swap trannys in my 74 chevy cheyenne heavy half ton 4x4

Discussion in 'Chevy C/K Truck Forum' started by jmiller5058, Oct 28, 2011.

  1. jmiller5058

    jmiller5058 New Member

    i want to take out the th350 trans and transfercase, i was told that the th400 is a four speed and another person said it wasnt i wouldnt mind having a 400 in but i was thinking of putting in a 700r4 in it to make sure i had the overdrive gear any advice on if i could put a 700r4 in my truck thanks
  2. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    If your looking for a 3spd with overdrive go with the 700R4.
    It has a friendlier gear ratio that'll help with mileage.
  3. Pedro

    Pedro New Member

    A common misconception with the 700r4 is that the overdrive gear ratio is higher, thus giving you better fuel economy. This is not true. The overdrive gear in the 700r4 is actually the same (or very close) as the 3rd gear in most of the TH400s and TH350s, from what I've understood. So you actually get the same fuel economy regardless of the transmission. The benefits of the 700r4 are lower gear ratios in the first three gears because it has the overdrive gear to shift into when at highway speed. One would choose the 700r4 if he wanted to have more torque at low speed. The 700r4 is my personal preference, but if you're frequently pulling a load or hauling the TH400 is the toughest transmission without doubt. The 700r4 has cooling issues when it is put under extreme work loads, but I've seen trucks with an extra transmission cooler to help with the excess heat. What are your intentions with this truck? Are you going to be off-roading, hauling, drving to work and back etc.???
  4. jmiller5058

    jmiller5058 New Member

    i drive to work and back and the third gear in a th400 is the same as the 700r4s fourth gear then? and i would be putting in a 700r4 from a 1986 chevy 4x4 into my 1974 chevy cheyenne 4x4 heavy half ton will it mount in i know i would have to modify the drive drive shafts and would a 700r4 bolt to my transfer case from my th350

    ---------- Post added at 09:07 PM ---------- Previous post was at 07:25 PM ----------

    and can i use my np 203 transfercase from my turbo 350 trans on the 700r4 trans
  5. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Gear ratios for the 700R4, Turbo350, and Turbo400 are as follows:

    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

    As you can see 3rd on all three trans are the same, the first two gears on a 700R4 are lower which will help with fuel mileage in traffic, and overdrive is spaced farther out to improve mpg even better on the highway.
    All transmissions like cooler fluid temps, to a certain extent, to cool and they can develop slipping issues.
    A medium sized cooler has been repeatedly proven to increase the longevity of 700R4 transmissions.

    You really need to look for a short shaft 700R4 to attach to the transfer case, personnally if I was replacing the trans with a low mileage take out I'd try to get the T case too and install it all as a complete unit.
    You may also need to have the driveshaft length changed to accomodate the new trans.
  6. Boonduff

    Boonduff Rockstar 4 Years 100 Posts

    You'll save a bunch of money using the transfercase that was bolted to the 700r4. The aftermarket adapters needed to bolt it to your stock transfercase be it a NP203 or NP205 are about $500. You also need to factor in the cost of lengthing your front driveshaft and shorting your rear shaft as the 700r4 and its transfercase will be longer then your stock units.
  7. jmiller5058

    jmiller5058 New Member

    but it will work in my truck
  8. jmiller5058

    jmiller5058 New Member

    i was told by two different guys that it wont bolt up to my transfer case and the other guy said as long as i have the adapter from the transfer case the 700r4 came with it should bolt right up the 700r4 is from a 86 chevy and i want to put it in my 74 chevy anymore advice would help alot
  9. Boonduff

    Boonduff Rockstar 4 Years 100 Posts

    The stock transfercase in your truck is either a NP203 fulltime 4x4 or NP205 parttime 4x4, usually in the 1974-1979 1/2 ton trucks the 205 only came with a manual trannsmission. Neither transfer case will bolt up to a 700r4 using any factory adapters. Also don't forget about the shaft stickout length and spline count on the transmission output and spline count on the input of the transfercase. The factory often used different spline counts and shaft lengths depending on different trannsmissions and transfercases. The guys I'd talk to if I were you would be either Novak conversions or Advance Adapters. They specialize in swapping drivetrain components and will give you info you can trust. I recently swapped a transmission in my Jeep and Advance was able to give me alot of helpful info.
  10. jmiller5058

    jmiller5058 New Member

    i looked on summit racings website they sell advanced adapters and the have an adapter to work with a 700r4 to a np 203 and my truck has the np203 is that all i will have to do to bolt it up

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