Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Diesel Transmission (3 speed to 4 speed)

Discussion in '1982-Present GM Diesel' started by aquaman02, Dec 14, 2002.

  1. aquaman02

    aquaman02 Newbie

    Joined:
    Dec 11, 2001
    Posts:
    4
    Likes Received:
    0
    Location:
    Tallahassee, FL
    Hey all,, have a question that I cant seem to find an answer to. I have a 1984 CUCV 6.2L with a 3 Speed THM-400 / 208 Transfer Case. It is mostly a road truck with some light off road use. I am not too fond of the high RPM's this thing is turning out and would like to make it a 4 speed. What do I need to do this.. Do I need to change the transmission to a 700 or can I just keep the THM-400 and swap the Transfer case for something else? Someone told me that I could just swap the transfer case and that would make it a 4 speed.. is this correct? /forums/images/graemlins/k5.gif
     
  2. u2slow

    u2slow 1/2 ton status

    Joined:
    May 9, 2001
    Posts:
    2,217
    Likes Received:
    0
    Location:
    BC Canada
    I different t-case won't help. I don't know of any with better than 1:1 ratio in high-range.

    A TH700 will fit your engine, but you'd need a different t-case, or at least a different input gear in the t-case to make it work.

    There is an auxiliary overdrive made by Gear-Vendors. It will cost you. And only works in 2wd since it bolts onto the back of the t-case.

    Bigger tires or different axle ratios are your alternatives.
     
  3. arveetek

    arveetek 1/2 ton status

    Joined:
    Mar 1, 2002
    Posts:
    722
    Likes Received:
    0
    Location:
    Granby, MIssouri, USA
    Perhaps somebody was thinking of a Gear Vendors or US Gear aux. overdrive transmission when they told you about swapping transfer cases.

    Both of these aux. transmissions work like a two-speed axle. They have direct and overdrive. This allows you to split all gears, so your three speed is, in essence, a six speed.

    The GV unit bolts on behind the TC, and can only be used in 2WD mode.

    The US Gear fits between the transmission and TC, and can be used in both 2WD and 4WD.

    Both units are expensive.

    Swapping to a 700 would probably be cheaper, but is still difficult. You have to move the TC back, and modify the driveshafts.

    Casey
     
  4. JORGE

    JORGE 1/2 ton status

    Joined:
    Jan 10, 2001
    Posts:
    213
    Likes Received:
    0
    Location:
    VITORIA-GAZTEIZ(ALAVA)BASQUE COUNTRY,SPAIN
    Why he needs an other T-case?I have the Th- 700- r4 with the Np208 from factrory...
     
  5. u2slow

    u2slow 1/2 ton status

    Joined:
    May 9, 2001
    Posts:
    2,217
    Likes Received:
    0
    Location:
    BC Canada
    The TH700 needs a 27-spline t-case input. The th400 uses a 32-spline. Ech tranny has its own adapter too.
     
  6. imiceman44

    imiceman44 1 ton status

    Joined:
    Aug 5, 2002
    Posts:
    15,160
    Likes Received:
    1
    Location:
    Sacramento, CA
    I agree that if you are not into heavy fourwheeling, you're better off with a 700, the 208 you have will need to be changed or swaped for one that goes on the 700.
    Where are you at?
    Fill out some of your profile like what city are you at and what year your vehicle is and what upgrades if any you have done to it.
    That sometimes helps people point you in the right direction, and for me here, it would let me know if you are close enough where I could trade you what you need. /forums/images/graemlins/smile.gif
     

Share This Page