Transfer Case Info for OEM Squarebodies

Discussion in 'Transfer Case' started by HotRodPC, Jul 16, 2012.

  1. HotRodPC

    HotRodPC Administrator Staff Member

    Posts:
    38,957
    Likes Received:
    167
    Joined:
    Aug 29, 2010
    Location:
    OKC, OK
    First Name:
    HotRod
    Truck Year:
    85
    Truck Model:
    Silverado K10 to K20 Conversion
    Engine Size:
    6.2 to Gas???
    The 4 transfer cases availalbe in Squarebodies from 73-91 were NP203, NP205, NP208 and NP241C. All are passenger side drops, and all are manufactured by New Process.

    Here is a little information on all of them. And we'll add more info as the thread grows. Soon, we'll have all the transfer case info all in one thread which comes in handy for doing conversions and modifications.
     
  2. HotRodPC

    HotRodPC Administrator Staff Member

    Posts:
    38,957
    Likes Received:
    167
    Joined:
    Aug 29, 2010
    Location:
    OKC, OK
    First Name:
    HotRod
    Truck Year:
    85
    Truck Model:
    Silverado K10 to K20 Conversion
    Engine Size:
    6.2 to Gas???
    Np203

    NP203
    Chevy, Dodge and Ford all used variations of this transfer case. All were chain drive to the front output. Some were full-time 4WD while others were part time. While the whole case is very large heavy and clunky, they have attained popularity through the use of the front "range box" section which is then adapted and mated to the front of another transfer case, a dual transfer case setup commonly known as a "Doubler".

    Transfer Case Specifications:
    Low Range reduction ratio: 1.96:1
    High Range: Direct (1:1)




    Chevy 203

    Input Spline: GM used three different input spline configurations on these cases.



    10 spline: (1971-79) Used behind SM465 transmissions



    27 spline: (1971-79) The units supplied with a T350 automatic have a 27 spline female input shaft.



    32 spline: (1973-79) This is the preferred shaft, as it is the strongest. These came behind Turbo 400 trannies.



    Bolt Pattern:

    Is an asymmetrical pattern unique to the 203. It is possible to disassemble this case and re-drill it for the 6 bolt circular pattern. An adapter is also available to mate this case to Jeep, Dodge or Ford 6 bolt circular applications: adapter PN AA50-0202
     
    Last edited: Jul 17, 2012
  3. HotRodPC

    HotRodPC Administrator Staff Member

    Posts:
    38,957
    Likes Received:
    167
    Joined:
    Aug 29, 2010
    Location:
    OKC, OK
    First Name:
    HotRod
    Truck Year:
    85
    Truck Model:
    Silverado K10 to K20 Conversion
    Engine Size:
    6.2 to Gas???
    Np205

    NP205

    The NP205 gear driven transfer case is considered by many to be the king of bulletproof. It was supplied in many GM, Ford, International and Dodge full-size trucks.

    GM NP205

    Note 8 bolt "racetrack" bolt pattern on early Chevy. Late Chevy will have the six bolt circular pattern, similar to the Ford, except the Chevy unit will have the front output yoke on the passenger side, like the early Chevy.

    Bolt Pattern:

    All GM NP205 cases 1971-1985 had a 8 bolt "racetrack" bolt pattern

    All GM NP205 Cases 1986-up had a 6 bolt circular bolt pattern

    Input Spline: GM Used four different input shaft configurations on these cases.

    10 spline (from SM465 Applications): (1971-85) The most common were units supplied with a 4 speed which typically had a 10 spline male input shaft.



    27 spline (from Turbo 350 applications): (1971-79) The units supplied with a T350 automatic have a 27 spline male input shaft.



    32 spline SHORT (appx 2" stickout)

    32 spl LONG a(appx 3-5/8" stickout)

    These are both from (Turbo 400 applications) (also some SM465 86-up may have used a 32 spl input.) We have seen both a short (about 2.0" stickout) and long (3-5/8"" stickout) versions of this gear. The adapter casting in both cases is 4-3/8" long. With the short input, the trans will have an output shaft that sticks out of the main case of the trans appx 4" With the Long input, the trans will have a shorter mainshaft: Sticks out of the main case about 2.5"



    1979 to 1985 GM NP205: 8 bolt "racetrack" bolt pattern:

    During these years, the GM NP205 showed up behind Turbo 400 and SM465 Transmissions in 1 Ton trucks only.. 1/2 and 3/4 T trucks began to be supplied with the NP208 instead. SM465 units will still typically use the 10 spline input. Turbo 400 units have the stout 32 spline female input (in most cases the short 32 spl input, about 1.5-2.0" stickout) however still uses the 8 bolt "racetrack" bolt pattern.

    1986 and Later GM NP205: 6 Bolt circular bolt pattern:
    At this point GM updated the unit to use the same 6 bolt circular bolt pattern used on the NP208, and all subsequent GM full size 4x4 truck applications. All of them are the 32 spline female input, although those we have seen are the long (about 3.5" stickout) 32 spl input.

    Front Output
    GM used two front output shaft configurations, one had a spline count of 10, the other was a 30 spline. 10 splines came before 1977 (roughly) 30 spline shafts came after 1977 (again, roughly). One quick way to tell them apart is by the fact that 10 splines came with a 1310 series yoke output, capable of accepting a CV or yoke driveshaft. 30 spline shafts came with the flat flange on the output, capable of accepting the GM 3R series CV joint.

    The 10 spline output will accept the stock 1310; Or a separately purchased 1330 or 1350 Spicer u-joint yoke, and the 1310 CV yoke. The 30 spline flange will accept the 1330 or 1350 CV joints.

    Rear Output
    The most popular version Is a 32 spline shaft / fixed yoke and will accept a 1310, 1330, or 1350 u-joint yoke, and the 1310 CV yoke.

    Some were slip yoke, with a longer tailhousing.

    NP205 Pics

    Round Pattern 32 Spline w/ Long Female Input:
    [​IMG]

    Racetrack Pattern 32 Spline w/ Short Input Female Input:
    [​IMG]

    Racetrack Pattern 27 Spline w/ Male Input (Used for Th350 and can be adapted to 700r4 also)
    [​IMG]
     

    Attached Files:

    Last edited: Jul 20, 2012
  4. HotRodPC

    HotRodPC Administrator Staff Member

    Posts:
    38,957
    Likes Received:
    167
    Joined:
    Aug 29, 2010
    Location:
    OKC, OK
    First Name:
    HotRod
    Truck Year:
    85
    Truck Model:
    Silverado K10 to K20 Conversion
    Engine Size:
    6.2 to Gas???
    Np208

    NP208

    Transfer Case Specifications:
    Low Range reduction ratio: 2.6 to 1
    High Range: Direct 1:1

    Chevy, Dodge and Ford all used variations of this transfer case. All were chain drive to the front output, with a light weight aluminum case. Most used a slip-yoke rear output. We are not aware of a Fixed yoke conversion for this case. While these units will hold up under moderately heavy off road use, they are not considered the preferred swap due to the chain drive and thin aluminum case.

    Bolt Pattern:

    6 bolt circular pattern. Note: This pattern is almost symmetrical, however it is not and will only bolt up one way. Chevy, Dodge and Ford all used the same bolt pattern, However with a different ROTATION of the pattern. Dodge and ford are close, and swaps might result in a useable Tcase droop angle, however Chevy units are about 90 degrees different and cannot be interchanged. Ford units have a driver side drop, While GM units are passenger side drop.



    Chevy 208



    Passenger side drop (front driveshaft). This Tcase has the GM rotation of the 6 bolt circular bolt pattern.


    Input Spline: We have run into two different input spline configurations on these cases.



    27 spline: The units supplied with a T350 or 700R4 automatic have a 27 spline female input shaft.



    32 spline: This is the preferred shaft, as it is the strongest. These came behind Turbo 400 or SM465 transmissions.
     
  5. HotRodPC

    HotRodPC Administrator Staff Member

    Posts:
    38,957
    Likes Received:
    167
    Joined:
    Aug 29, 2010
    Location:
    OKC, OK
    First Name:
    HotRod
    Truck Year:
    85
    Truck Model:
    Silverado K10 to K20 Conversion
    Engine Size:
    6.2 to Gas???
    Np241c

    NP241C

    Starting in about 1987, the New Process 231/241 series transfer case became standard in Jeep, Dodge, and Chevrolet applications. These transfer cases are part time 4WD (Shift positions 4HI - 2HI - N - 4L). They have a relatively thin aluminum housing. They are 1:1 direct drive in high range, and use planetary reduction gears for low range with a ratio of 2.72:1 They use chain drive for the front output. The NP241 was typically used in V8 applications.

    Exact identification:

    These New Process cases have a circular plate, about 2" in dia., on the rear of the case, in the center. Full identification info for the case is on this plate

    Bolt Pattern:
    Jeep, Dodge and Chevy versions all use a 6 bolt circular bolt pattern. This pattern is NOT symmetrical and will only bolt up one way. You can typically bolt a Jeep unit to a Dodge transmission and vice versa, however Chevrolet units are NOT cross compatible: While GM uses the same 6 bolt patter, they have it rotate approximately 90 degrees from that used by jeep dodge.

    In all of these 6 bolt applications the Klune-V Extreme Underdrive will bolt up to these transfer cases directly with adapters necessary. Some may require a spacer.

    Slip-Yoke Eliminator
    All of these units we have seen have been equipped with a slip-yoke rear output. Slip-Yoke Eliminator kits are available for most of these transfer cases

    GM New Process 241 Transfer Case
    In 1988, GM began using the NP241 transfer cases. Most of these units will be right hand drop, but Chevy also used a few left hand drop applications. The Chevy NP241 is supplied with a 27 spline female input or a 32 spline female input. With a T350, 4L60E or 700R4 tranny, it will be 27 spline. With a T400 or 4L80E trans or 5 speed, it will be 32 spline.
     
  6. 89Suburban

    89Suburban Full Access Member

    Age:
    43
    Posts:
    22,543
    Likes Received:
    72
    Joined:
    Dec 7, 2010
    Location:
    Southeast PA
    First Name:
    Paw Paw
    Truck Year:
    1990 Chevy Suburban
    Truck Model:
    R-1500
    Engine Size:
    5.7L TBI/700R4/3.73 10 Bolt Auburn L-S /Cat-Back
    Good info.
     
  7. bucket

    bucket Super Moderator Staff Member

    Posts:
    12,969
    Likes Received:
    67
    Joined:
    Aug 3, 2010
    Location:
    Usually not in Ohio
    First Name:
    Andy
    Truck Year:
    '77, '79, '84, '88
    Truck Model:
    K5, K30, C10, K20 Burb
    Engine Size:
    350-454
    Couple things. The 32 spline input on the 203 was used through the '79 model year, and most (if not all) '88 squarebodies had the 208.
     
  8. thaifighter

    thaifighter Banned

    Age:
    50
    Posts:
    76
    Likes Received:
    1
    Joined:
    May 8, 2012
    Location:
    chilliwack british columbia
    First Name:
    brian
    Truck Year:
    81
    Truck Model:
    k20custom deluxe 16.5 rims
    Engine Size:
    350 sm465/np208
    Nice write up
     
  9. HotRodPC

    HotRodPC Administrator Staff Member

    Posts:
    38,957
    Likes Received:
    167
    Joined:
    Aug 29, 2010
    Location:
    OKC, OK
    First Name:
    HotRod
    Truck Year:
    85
    Truck Model:
    Silverado K10 to K20 Conversion
    Engine Size:
    6.2 to Gas???
    You mean nice Copy and Paste. :rofl: Taken from a Transfer Case parts supplier. Yes, they did do pretty good on the info. :High 5:
     
  10. oneluckypops

    oneluckypops Full Access Member

    Age:
    36
    Posts:
    2,182
    Likes Received:
    13
    Joined:
    Feb 6, 2011
    Location:
    Sedalia, Mo.
    First Name:
    Luke
    Truck Year:
    85
    Truck Model:
    K30 SRW
    Engine Size:
    5.7 Fuel injected Vortec/ 4L80E
    good info, BUT in 1979 the NP205 was NOT just in the 1 ton's. My 79 shortbed 1/2 ton with the sm465 had a NP205 from the factory.
     
  11. HotRodPC

    HotRodPC Administrator Staff Member

    Posts:
    38,957
    Likes Received:
    167
    Joined:
    Aug 29, 2010
    Location:
    OKC, OK
    First Name:
    HotRod
    Truck Year:
    85
    Truck Model:
    Silverado K10 to K20 Conversion
    Engine Size:
    6.2 to Gas???
    Yep, and ALL 80 models had it, no matter what trans or model. I figured there'd be corrections needed to this stuff.
     
  12. bucket

    bucket Super Moderator Staff Member

    Posts:
    12,969
    Likes Received:
    67
    Joined:
    Aug 3, 2010
    Location:
    Usually not in Ohio
    First Name:
    Andy
    Truck Year:
    '77, '79, '84, '88
    Truck Model:
    K5, K30, C10, K20 Burb
    Engine Size:
    350-454
    Other than some rare '73-'74 trucks, every sm465 equipped truck got the np205. And actually, most people don't realize that automatic-equipped '77-'79 1-tons got the np203... not the np205.
     
  13. HotRodPC

    HotRodPC Administrator Staff Member

    Posts:
    38,957
    Likes Received:
    167
    Joined:
    Aug 29, 2010
    Location:
    OKC, OK
    First Name:
    HotRod
    Truck Year:
    85
    Truck Model:
    Silverado K10 to K20 Conversion
    Engine Size:
    6.2 to Gas???
    I thought ALL 73's got NP205? As did ALL 80 models got NP205.

    I just know I need an NP205 round pattern from an 86 up. That's gonna make it a tough find.
     
  14. Kapdin

    Kapdin Full Access Member

    Posts:
    801
    Likes Received:
    11
    Joined:
    Jul 26, 2012
    Location:
    North Dakota
    First Name:
    Lance
    Truck Year:
    1977,1979,1984,1987,1988
    Truck Model:
    Silverado K30, Scottsdale K20, Silverado C10, Silverado V10, Silverado V20
    Engine Size:
    400ci, 350ci, 350ci, TBI 350ci, TBI 350ci
    Hey gents, was drinkin with the family last night and got to talkin with grandpa (who i got the truck from) and he started saying that that np203 full time is only full time upto 35mph????? input please.
     
  15. 89Suburban

    89Suburban Full Access Member

    Age:
    43
    Posts:
    22,543
    Likes Received:
    72
    Joined:
    Dec 7, 2010
    Location:
    Southeast PA
    First Name:
    Paw Paw
    Truck Year:
    1990 Chevy Suburban
    Truck Model:
    R-1500
    Engine Size:
    5.7L TBI/700R4/3.73 10 Bolt Auburn L-S /Cat-Back
    Myth, sorry.
     

Share This Page