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NP203

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Calclips, Dec 18, 2001.

  1. Calclips

    Calclips 1/2 ton status

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    Can anyone tell me about the NP203 T-case? I don't know much about those... you guys don't talk about them much. All I hear is 205, 205, 205. Thanks in advance to anyone who posts useful info!
     
  2. vince13

    vince13 1/2 ton status

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    203's are good t-cases for stock vehicles, they are strong but the chains tend to stretch and then break with lager tires but can be rebuilt to accomodate larger tires. they also have a lower low range than a stock 205. which is good for climbing and accomodating for larger tires. currently i have a 203 in my 73 blazer it is stock and never been rebuilt(soon tho) and i am running 36 inch swampers and 1 ton diffs. so it is pulling a lot of extra weight. and it seems to work just fine hasn't given me any grief in the 4 years i have wheeled it. and that low range sure is fun in the mud. overall they are a good t-case. thats my 2 cents anyways

    73 Blazer 1Ton 6inch lift, 3 inch body, 36 inch swampers
    79 3/4 ton suburban, soon to be 6 inch lift, 3 inch body, and 44 in boggers. Oh ya
     
  3. Calclips

    Calclips 1/2 ton status

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    okay, thanks again. I found a 79 chevy (its a pickup, I'm sorry) with a 350, th350, and a 203. Its solid for a 79, box needs a little work... but nothing major at all. Guy is asking 1850 for it which seems like a pretty good deal. I noticed some ATF fluid arround the tranny pan, but thats most likely only a gasket and the leak didn't look major. One thing I did notice was a slight tick when your in the cab. Didn't sound like a lifter tick and definately not a rod knock. I think its just an exhaust leak somewhere along the line. I think the truck looks like a good deal.
     
  4. Executioner

    Executioner 1/2 ton status

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    WRONG, the NP203 and NP205 have the same Low Range.
    1.96:1, and 2.0:1 are for all applications the same !
     
  5. Blazer79

    Blazer79 1/2 ton status

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    It's a full-time transfer case. It has a differential for use in paved streets and so. When you engage any of the "LOC" positions, it locks this differential so it works like any other 4wd. You'll love not having to get down and get all muddy just to lock your hubs. Also, the full-time 4wd gives you better grip in curves and slippery situations.

    Make sure you use 10w30 engine oil in this transfer case, not ATF or gear lube.

    <font color=purple>//////
    <a target="_blank" href=http://blazer79.freeyellow.com>blazer79.freeyellow.com</a></font color=purple><font color=black>
    Soon a 454 K5!!</font color=black>
    [​IMG]
     
  6. 72gmc-burb

    72gmc-burb Registered Member

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    Mile Marker makes a conversion from full time to part time for the NP-203 transfer case. It will set you back under 60 bucks + the cost of your locking hubs. Many folks have done this to there 203's over the years (especially during gas crunch). The conversion removes the differential from the case. Also, the chain driven 203 is typically less noisy than a gear driven 205. However, I wouldn't reccomend a 203 for over 300hp applications.

    Hubcap
     
  7. Executioner

    Executioner 1/2 ton status

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    FYI, they (GM) but them behind 454's and grany gear 4 -speeds.
    A brand new NP203, and a brand new NP205 are really about the same in streght.
    After 20 years YRWV.
     
  8. vince13

    vince13 1/2 ton status

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    I don't think so the 203 is 2.01:1 Low Range , and the 205 is 1.96:1 Low Range, therefore the 203 has a lower gear ratio. and it does make a difference. So they are not the same close but not the same.

    73 Blazer 1Ton 6inch lift, 3 inch body, 36 inch swampers
    79 3/4 ton suburban, soon to be 6 inch lift, 3 inch body, and 44 in boggers. Oh ya
     
  9. Calclips

    Calclips 1/2 ton status

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    So, how exactly does this work? Is there a 2wd at all, or is it always 4wd. The truck has locking hubs on the front of it, so I assume that it can't be in 4wd all the time. I just know that stock for that year was a 203 with that tranny, and it isn't a 205. What does a 208 look like? It may be one of those....
     
  10. bigredblazer

    bigredblazer 1/2 ton status

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    even with the hubs everything is spinning in the diffs, and transfer case, UNLESS there is a part time kit in it. The best thing for a 203, is to be bolted in front of a 205! I've had two Blazer's, and a POS Dodge with 203, and never had any problems, although something will happen sooner or later with some serious wheeling. Jon

    Blazin' Trails ORD Style
     
  11. mkmiller

    mkmiller 1/2 ton status

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    One thing that I noticed wasn't mentioned was the shift pattern of the 203. I don't know it and I have one! Anyone else?

    '71 K5 350/350/203
    Magnolia,AR
    You drive a Jeep? But shouldn't that little
    thing have training wheels?
     
  12. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    203 is one tough case. Look at it this way. In it's original version they run for years and 100's of thousands of miles without problem. That's the truck in 4wd for a long time. My 75 has over 200k on it and I just have replaced the worn chain. That's $130 in parts in 25 years and 200k. Pretty good track record. My wifes 79 was converted when we got it. It had a crappy superwench kit in it that I ended up having to replace about a year after we go it. Chain is still tight in it.
    From the age of the hubs I guess it got converted in the early 80's. It has Wolvorine hubs and the superwench bought the rights to the kit that was originaly packaged with those hubs in the 80's.
    I only converted my 75 to part time for 1 reason. I now run a front locker. I have put some serious though to putting the spider gears back into the front so that in the winter I can have the full time back.
    Now to answer a few of the other questions that came up in this post.
    In stock form the shift pattern is
    L LOC
    Low
    N
    High
    H LOC.
    The LOC posistions lockes the Diff that is located in the transfer case so you get a 50/50 power split to the axles.
    In high and low the Diff in the case is active and it is possible for all the power to go to either axle if you get wheel slip.
    When converted the LOC posistions become your 4X4 modes.
    The High and Low are 2wd and yes you end up with 2wd LOW.
    Now there is a problem with converting theses cases to part time and this is where most of the undeserved bad rep has come for the 203. The case was designed to use the oil slung off the chain to help lubricate the case. When you part time them the chain is no longer spinning and no longer lubricating. The big problem is in the tail shaft housing is a resivior. It catches slung oil. this oil is then piced up by a pump (plastic gear) and it pushes the oil into the tail shaft bearings and some of it goes up a oil jounal in the shaft and lubricates the upper chain gear bearings. Well when that resivior runs dry so do the tail shaft bearings.
    When you convert a 203 you MUST put it into LOC ( leave the hubs unlocked) every 200 miles or so and drive it a couple of miles to replenish the oil in the resivior.
    Over filling these cases is not a bad idea and will get the oil up so it sloshes into the resivior on take off or up hills.
    These cases also run ENGINE OIL not gear oil. Same flavor you run in the motor is fine. Gear oil in cold climates gets to thick and with break the plastic pump. Often ATF is mistakenly put into these cases. I have as yet to find anyone that says ATF has damaged them. ATF is reasonable lubricating properties and excelent cleaning but Oil is what belongs in it. If you find that ATF is in your case I would not be worried that it is possibly damaged. If Gear oil is in the case then take the small section off the tail cone and inspect the pump.
    To get the small section off you need to remove the rear yoke and the 6 (I think that's right) bolts that hold the very last section of the tail cone on. Take it off slow because the pump and spedo gear may fall off and have a catch pan ready. Pay close attention to what way the gear and pump go. That section has a O-Ring so you will not need a new seal unless the ring tears (not common). While you have it appart you may want to replace the tail shaft seal and the rubber seal under the washer on the yoke.
    If the pump is not broken then your ok The rest of the case will be fine with the gear oil. In warmer climates it is usualy ok. It's when you get places where the temp stays real low in the negatives that it will ruin the pump.

    Women dig dents and flat paint!
    coloradok5.com/gallery/Grim
    75 Jimmy, Dollar
    Grim-Reaper
     
  13. michaelm

    michaelm 1/2 ton status

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    how do you know it isnt a 205?
    a 208 is all aluminum.
    2.01 and 1.96 are so close that you wouldnt be able to tell the difference, what about 2.5% diference? funtionally the same
     
  14. Calclips

    Calclips 1/2 ton status

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    A 205 has a circular plate in the middle of it with 3 bolts in it. This case does not have one. At least it dosen't have one on the back side of it. If that plate is on the front side of it... it may be a 205... I didn't look at that side.
     
  15. michaelm

    michaelm 1/2 ton status

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    if it is cast iron and has free wheeling hubs then it is a 203 with a kit in it
     
  16. Calclips

    Calclips 1/2 ton status

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    Yeah, <a target="_blank" href=http://www.off-road.com/chevy/mm-np203/>http://www.off-road.com/chevy/mm-np203/</a> says that 203's are cast iron, and about 300lbs. The tailcone on them is aluminum on them (according to the link)
     
  17. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    300lb....Uhhh they are heavy but I would guess more like 200lb tops with fluid. I have dead lifted mine. Wasn't easy and I'm no wimp but I seariously doubt I could dead lift more than 200lb.
    Now maybe I missed a post or something but what year of a truck are you looking at? 203's were dropped for the 80 model year. In 80 all trucks got 205's. in 81 the 208 showed up. 205 was still behind some 3/4 and 1 ton trucks and I think in 90 is when the 241 came in. The only truck listed in your bio is a 90.

    Women dig dents and flat paint!
    coloradok5.com/gallery/Grim
    75 Jimmy, Dollar
    Grim-Reaper
     
  18. Calclips

    Calclips 1/2 ton status

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    I'm talking about a 79 half ton with a TH350 tranny. I'm just gathering info on what may be a purchase. And while were on the subject that its a 79... will a stock front driveshaft fit it with a 6" lift. There isn't one on it now. I won't be doing much serious offroading where alot of suspension travel is necessary. Mostly mud and mild trail riding.
     
  19. Boss

    Boss 1/2 ton status Author

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    79' 1/2 ton with the TH350, yep, it's a 203 alright.
    NP241 came in 89' btw. Just a little info.
    As far as a stock drive shaft working with 6" lift. I would say so. It will be close though.
    Boss

    Pic of my truck Before N' After
    <a target="_blank" href=http://coloradok5.com/gallery/BeforeNAfter>http://coloradok5.com/gallery/BeforeNAfter</a>
     
  20. BorregoK5

    BorregoK5 1/2 ton status

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    I have a 79 w/203 and 4" of lift on a stock front shaft and it is flexed to the maximum at full droop. You can purchase a spacer to put on the cv end in cases where you have a 6" lift but I haven't seen one in use.

    I started with nothing and I still have most of that left! - <a target="_blank" href=http://www.echobit.com:81/k5/> Pictures</a>
     

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