1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

TH400 What years and models?

Discussion in 'Transmission & Transfer Case' started by SCOTT CLEAVER, Sep 11, 2019.

  1. SCOTT CLEAVER

    SCOTT CLEAVER Junior Member

    Posts:
    3
    Likes Received:
    0
    Joined:
    Sep 11, 2019
    Location:
    33914
    First Name:
    scott
    Truck Year:
    1983
    Truck Model:
    k10
    Engine Size:
    350
    I am looking to start a project. Shortbed K10. prefer to get a TH400 to start with. Are certain years or engine tranny combos the best place to look in order to have a 400?
    Thanks Scott
     
  2. 1987 GMC Jimmy

    1987 GMC Jimmy Automobile Hoarder

    Age:
    22
    Posts:
    5,244
    Likes Received:
    1,662
    Joined:
    Jan 23, 2016
    Location:
    Mississippi
    First Name:
    Jesse
    Truck Year:
    1987
    Truck Model:
    V1500 Jimmy
    Engine Size:
    350
    You’re gonna find them in 3/4 and 1 tons mostly. 454 will be guaranteed to have a TH400, but keep an eye out for the 6.2 diesels and 350s. If I were you, I’d find a motor home that’s based on a Chevy P30 chassis being sold cheap or parted out. You’ll find in there a pristine TH400 that shifts like a dream 99/100 times. Hell, I’d yank the whole running gear. As with all the longitudinal GM trannies of this era, the later model, the better.
     
    Larry Olson and donnieray like this.
  3. Matt69olds

    Matt69olds Full Access Member

    Posts:
    419
    Likes Received:
    350
    Joined:
    Jan 8, 2018
    Location:
    Central Indiana
    First Name:
    Matt
    Truck Year:
    81
    Truck Model:
    GMC 1/2 ton
    Engine Size:
    455 Olds
    Other than valve body calibration, the 400 hasn’t changed much since it first came out in 65. In 1969, Hydromatic changed the center support by machining an extra .040 off the case lugs. They added a .040 snap ring under the center support. This prevented the center support from wearing the case. In 1971, the desirable smooth race direct drum was replaced with the weaker roller clutch style. The later drum can’t be upgraded to a 34 element sprag The early style drum returned with the introduction of the 4L80 trans. In the mid 70s, the aluminum pistons were replaced with less desired stamped steel. This was a cost savings change. The aluminum accumulator piston in the valve body was also changed to plastic, they break and should be replaced. The aluminum pistons are getting kinda hard to find. The 4L80 bonded direct drum piston will retrofit into the 400.

    Ideally, find a core between the years of 1965 and 1971. If the core is older than 69, upgrade to the later center support and include the .040 snap ring. If it’s newer than 71, used a 4L80 direct drum and install a 34 element sprag.

    Some motor homes and big trucks used straight cut gears, those transmissions are known as 475. Some also use parking brakes on the output shaft and extension housings. They can be replaced with normal 4wd and 2wd output shafts and extension housings.

    Hope that helps.
     
    Larry Olson, fried_daddy and Rickf like this.
  4. Charlie

    Charlie Full Access Member

    Posts:
    1,627
    Likes Received:
    673
    Joined:
    Aug 2, 2017
    Location:
    Euless, Texas
    First Name:
    Don
    Truck Year:
    1974
    Truck Model:
    Cheyenne 10 LWB
    Engine Size:
    350/TH350/AC/4 BBL Quadrajet
    :welcome:
     
  5. nvrenuf

    nvrenuf Full Access Member

    Posts:
    663
    Likes Received:
    129
    Joined:
    Jul 30, 2010
    Location:
    Mobile, Al.
    First Name:
    John
    Truck Year:
    1991
    Truck Model:
    K5
    Engine Size:
    454
    Do yourself a favor and buy a trans / tcase combo together. The tailshaft lengths can change based on the tcase (NP208, NP205, NP203). In addition, the year of the tcase can effect the adapter and trans tailshaft length required. Also, tcases that were originally behind other types of transmissions will typically have the wrong spline count input creating additional work for the conversion to fit a th400.

    Your build will be simpler if you purchase these combo unit so you have all the right parts.
     
    Larry Olson and Arkansas_V8 like this.
  6. SCOTT CLEAVER

    SCOTT CLEAVER Junior Member

    Posts:
    3
    Likes Received:
    0
    Joined:
    Sep 11, 2019
    Location:
    33914
    First Name:
    scott
    Truck Year:
    1983
    Truck Model:
    k10
    Engine Size:
    350
    Thanks all. Good advice.
     
  7. Craig 85

    Craig 85 Full Access Member

    Posts:
    1,877
    Likes Received:
    1,172
    Joined:
    Jan 25, 2017
    Location:
    Grass Valley, CA
    First Name:
    Craig
    Truck Year:
    1985
    Truck Model:
    K30 SRW
    Engine Size:
    454/TH-400/NP205
    The 4x4 cases are different than the passenger car case. Look for 3 threaded bolt holes flanges near the torque converter (lower right).

    4WD
    [​IMG]

    2WD
    [​IMG]
     
  8. Matt69olds

    Matt69olds Full Access Member

    Posts:
    419
    Likes Received:
    350
    Joined:
    Jan 8, 2018
    Location:
    Central Indiana
    First Name:
    Matt
    Truck Year:
    81
    Truck Model:
    GMC 1/2 ton
    Engine Size:
    455 Olds
    I guess I forgot to mention the difference in 4x4 cases. I hang my head in shame.
     
    JoeR Jr and SCOTT CLEAVER like this.
  9. nvrenuf

    nvrenuf Full Access Member

    Posts:
    663
    Likes Received:
    129
    Joined:
    Jul 30, 2010
    Location:
    Mobile, Al.
    First Name:
    John
    Truck Year:
    1991
    Truck Model:
    K5
    Engine Size:
    454
    The HD cases, like pictured above, can also be found in some 2wd's they're just more plentiful in 4wd's. I don't know what dictates when a 2wd gets the HD case though, when used in a 2wd the bosses are there but undrilled because they still use the thin tin cover. Years ago, I scored an undrilled HD core cheap from a 4.6 v6 Astro van.

    The HD cases started in 4wd's around 78-79, in 2wd's it was somewhere in the mid 80's.
     
  10. SquareRoot

    SquareRoot Full Access Member

    Posts:
    324
    Likes Received:
    243
    Joined:
    Mar 18, 2017
    Location:
    Arizona
    First Name:
    Mike
    Truck Year:
    85
    Truck Model:
    K20
    Engine Size:
    350
    I'm about to yank my completely rebuilt (650 ish miles ago) th400/208 t-case out of my 85 K20 so I can install my completely rebuilt (0 miles ago) nv4500/205 t-case. Just saying.
     
  11. SCOTT CLEAVER

    SCOTT CLEAVER Junior Member

    Posts:
    3
    Likes Received:
    0
    Joined:
    Sep 11, 2019
    Location:
    33914
    First Name:
    scott
    Truck Year:
    1983
    Truck Model:
    k10
    Engine Size:
    350
    SquareRoot,
    Shame were not closer
     
  12. 73c20jim

    73c20jim Supporting Member Supporting Member

    Age:
    74
    Posts:
    1,494
    Likes Received:
    756
    Joined:
    Jun 11, 2018
    Location:
    Tombstone, AZ
    First Name:
    Jim
    Truck Year:
    1973, 1973
    Truck Model:
    C20 2WD Custom Deluxe. C10 2WD Base Model
    Engine Size:
    350 CID 195/260 HP Goodwrench crate, 400 CID 2bbl
    Got a 2bbl 400 CID motor for sale in southern AZ, if that helps? And TH375 trans.
     
  13. fried_daddy

    fried_daddy Full Access Member

    Posts:
    186
    Likes Received:
    141
    Joined:
    Apr 7, 2019
    Location:
    High Point, NC
    First Name:
    Matt
    Truck Year:
    1987
    Truck Model:
    R1500
    Engine Size:
    4.3
    My 87 R1500 came with a HD case TH400 behind the factory 4.3L engine. With the bosses drilled and the heavy duty 6 bolt dust cover. I think I was the first person to open that transmission up because it was sure in rough condition after 30+ years.
     
    nvrenuf likes this.

Share This Page