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Swapping NP203 to NP205

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by reddog64, Mar 15, 2001.

  1. reddog64

    reddog64 1/2 ton status

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    I have a th350 w/a np203 and want to go to the np205... my np203 is slowly dying... I had my rear driveshaft out last night and it still clunks when moving from a dead stop... It's gotta be the transfer case... How difficult is it gonna be to go to the np205 from the np203? Will the 205 bolt to a th400 better than the th350??? Will I need new drive shafts again?

    Um... yes officer I know it's too big...
     
  2. HarryH3

    HarryH3 1 ton status Author

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    Has your 203 been converted to part time? Perhaps with one of those el-cheapo kits that basically jams the internal diff? If so, then it's probably that those little jamming gears are worn and causing the clunk. If not, then the chain that drives the front output could be stretched. The 203 is a pretty strong t-case. Just make sure the chain doesn't get stretched too far and they'll last forever.

    It's way cheaper to fix or replace your 203. To go to the 205 you'll have to change the t-case, adapter, driveshafts and shifter. Low range is virtually the same with either case, so I wouldn't go to all the trouble of making that swap.

    <font color=black>HarryH3 - '75 K5</font color=black>
    <A target="_blank" HREF=http://ThunderTruck.ColoradoK5.com>http://ThunderTruck.ColoradoK5.com</A>
     
  3. rich

    rich 1/2 ton status

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    I am in the middle of the same swap right now. The NP203 is about 11 inches shorter than the 205, so you'll definitely need a different rear driveshaft. I have factory front driveshafts for both, and I know they are slightly different in length, but I can't remember how much difference there is or which is longer.

    As for which transmission they bolt to "better"- whatever type of trans the T-case came off of is what it will bolt back onto. So if you find an NP205 for a TH350, then it will fit a TH350 fine, and if you find one from a TH400, then it will fit a TH400. The input splines of the T-case are specific to each different trans - the TH400 has 32 splines and the TH350 has 27 I think. Also the adapter between the T-case and trans is specific to each trans.

    Hope this helps! I can measure the factory front TH350/NP205 driveshaft for you if you need the measurement. I don't have a rear driveshaft for it yet, so I can't get a measurement for that.

    Richard
    Raleigh, NC
    '90 K-5 Blazer - stock, daily driver
    '76 K-5 Blazer - 14-bolt FF, 4.10's, locked front and rear, 36's, SM465/NP205
     
  4. Wheels

    Wheels 1/2 ton status

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    If you get a 205 that has a 350 adaptor on it, it will bolt up directly. For GM 205 applications, there are three different adaptors, TH350, TH400, and the SM465. The TH400-NP205 has a larger input bearing. The others have different input shaft spline counts. The strut rod the goes from the bell housing (bottom right hand bolt) to the side of the transfer case will have to be shortended. Rear drive shaft will have to be lengthened about 8 to 10 inches and the front will have to be shortened. If you dont have automatic or manual hubs, you will need them for the 205.
     
  5. reddog64

    reddog64 1/2 ton status

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    Well, my buddy woks at a towing yard, he drives the truck, you know how handy a tow truck boom is for pulling a 454 and tranny.. took 10 minutes last night, no joke... course the fenders and cab were off... hahaha.. anywyas...
    I can get a used np203 for next to nothing, but I'd have to rebuild it.. what is the cost on a kit to rebuild a 203 with a part time kit in it.. mine currently has the part time kit, but I dont wanna take mine out till I have one to put in it... What does the rebuild kit cost...

    Um... yes officer I know it's too big...
     
  6. HarryH3

    HarryH3 1 ton status Author

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    Here's the best way to do the conversion to part-time: <A target="_blank" HREF=http://www.milemarker.com/catalog/4-x-2-conversion.html>http://www.milemarker.com/catalog/4-x-2-conversion.html</A>. That shaft at the top of the page gets installed into your 203. It's the right way to do the conversion.

    The low-budget conversion kit is the one further down the page that has what looks like 4 pieces of a gear. Those are probably what's in your current t-case and most likely the cause of the slop that's in it.

    Not sure of the cost of a 203 rebuild kit. Perhaps someone else here can fill you in on that.

    <font color=black>HarryH3 - '75 K5</font color=black>
    <A target="_blank" HREF=http://ThunderTruck.ColoradoK5.com>http://ThunderTruck.ColoradoK5.com</A>
     
  7. Mudzer

    Mudzer 1/2 ton status Author

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    I would say go for it, the NP205 is way better. I once had an NP203 with part time kit and I suffered the same symptoms. I have since installed a SM465 and NP205 tranny. Now, with my SM465 and NP205 install, I used a factory part for my rear bumper, but this will probably not work for your application. I used the rear section of a two piece driveshaft from a 3/4 ton Chevy 2wd truck. I removed the front portion of this two piece shaft (it slips off), then I removed the carrier bearing from the driveshaft. Next, I used my NP203 rear drivesaft yoke (front portion of the driveshaft non-slip style) and slipped it over the splined portion of the 3/4 ton shaft. And it worked! I did remove some from the splines because it would bottom out, but not too much. Look for 2wd driveshafts at local junkyards. Now, if you get a slip yoke style NP205, you will have to modify a longer shaft from a 4wd long bed truck. This could be done by any driveshaft shop very cheap. Up front, I again used my NP203 shaft and had it cut down. I think when you use the SM465, your NP205 sits about 8" more forward than the NP203 with TH350, but not sure about just changing transfer cases. Check out Offroad Design webiste under the doubler section. Stephen lists several adaptor lengths so you could get an idea. My tranny and case fit perfectly in the same holes on the crossmember, plus I used the same crossmember from my NP203 setup.

    Mudzer 1978/91 K5
    <font color=blue>www.mudzer.coloradoK5.com</font color=blue>
     
  8. Bowtie85

    Bowtie85 Straight outta Yorkton Premium Member

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    Bump, google brought this thread up.

    As well as this from 67-72 trucks:

    Most 1973 - 1980 GM Trucks had.
    4spd/NP205 10 Spline (part time 4wd)
    4spd/NP203 10 Spline (full time 4wd)
    Turbo 350/NP203 27 Spline (full time 4wd)
    Turbo 350/NP205 27 Spline (part time 4wd) I think, 1973 and 1980 Only
    Turbo 400/NP203 32 Spline (full time 4wd)
    Turbo 400/NP205 32 Spline (part Time 4wd)
     
  9. max 02

    max 02 N.E.D. Premium Member

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    Gotta love the old threads!

    Looks like I should save that two piece drive shaft I got in the back yard...you never know what it might fit!?? :haha:
     
  10. Bowtie85

    Bowtie85 Straight outta Yorkton Premium Member

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    I should just drop a 2wd trans in and call it a day. :haha:
     
  11. max 02

    max 02 N.E.D. Premium Member

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    We are in Canada! Not Michigan! :haha:
     

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