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NP208 slip yoke eliminated!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Blue85, Mar 28, 2004.

  1. Blue85

    Blue85 Troll Premium Member

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    Formula: 1 Chevy NP208 + 1 Dodge NP208 + 1 modified case piece from K10ANDYKHAMNIC = Longer driveshaft - no slip yoke binding + ability to run without a rear driveshaft[​IMG]

    This adds a good 6" to the driveshaft. I did a rebuild at the same time, so I needed parts for this. The only other part I needed was a Dodge speedometer gear, since these parts are not interchangable from Chevy to Dodge.
    [​IMG] This gives a comparison of the Stock style (left) to the modified version, even though the case on the right it empty. Modifications Andy did to the case include:
    -New drain plug up high in the Chevy location (Dodge puts it down lower)
    -Threaded acceptor for support rod bolts (Dodge doesn't use the bellhousing to T-case support rods)
    -New bung to accept the shift rod on the inside of the case.
    [​IMG]
    [​IMG]

    For a driveshaft, I used part of a 91 3/4-ton Suburban shaft. The sub uses a two-piece shaft, but a K5 is about half a block shorter, so I only used one piece, the one with the slip splines. It uses the 1350 U-joints, too. This is actually within an inch or so of being the right length with my 14B s/f rear end. I just ripped off all of the carrier bearing stuff.
     
    Last edited: May 16, 2005
  2. camiswelding

    camiswelding 1/2 ton status

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    wow... nice job .. let us know how it works in real life ...
    a tech write up if the acid test works would really be cool!!!...
    I have the 208 in my blazer but its being replaced with a 205,,, but your piece would be fun to build...
    thanks
    cam
     
  3. Storm Trooper

    Storm Trooper 1/2 ton status GMOTM Winner

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    Nice! I'd like to see a write up on this also or just keep a list of the changes & parts required and let us know after the testing. Thanks for the imfo. /forums/images/graemlins/waytogo.gif
     
  4. cybrfire

    cybrfire 1 ton status Vendor GMOTM Winner

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    I'll third the tech write up!
     
  5. thebigdaddyof2

    thebigdaddyof2 1/2 ton status

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    Blue85, just posing the question,
    Did you look into using the front portion of the Dodge case...(just swapping the input shaft)?
    I have heard some talk of this but never really heard that it works or not.

    A write-up on your swap would be a great idea.
     
  6. Blue85

    Blue85 Troll Premium Member

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    Well the input shaft or even the whole planetary gearset can be swapped. As for using the whole Dodge case, I know that it would end up being clocked differently, but I didn't really investigate what the difference would be. The Dodge case has 6 studs coming out of it, but I believe these could be removed to accept bolts in the Chevy style. I didn't compare the bolt patterns, but they are at least similar and use 6 bolts each. Of course the Dodge case doesn't have the holes for the support rod, but some people run without that rod anyway. The shifter lever outside the case is different, but could probably be swapped. K10ANDYKHAMNIC could probably answer more of these questions.

    The swap does require a Dodge speedometer gear, but the Chevy cable does connect directly to it. However, it is on the opposite side of the case, so the cable has to be rerouted.

    One of the hardest parts for me has been finding a rear output yoke. The case came with a 1310 yoke, but who wants that? I am still running in front wheel drive looking for an equivalent 1350 yoke.

    Anyone interested in doing this swap should contact Andy, as he knows the mods needed for the case and can do them. With his back case half and the whole Dodge 208 I got from a junkyard, I spent less money than the SYE kit that is available for the NP241.
     
  7. skratch

    skratch 1/2 ton status

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    What parts exactly do I need to look for to do this mod?

    I have a spare 208 case already and I would love to go without that slip yoke on my Burb, until I get my doubler.
     
  8. Blue85

    Blue85 Troll Premium Member

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    The bug with using the whole Dodge case is that the 6-bolt mounting pattern is not quite symmetrical and the Chevy version is about 90 degrees different than the Dodge.

    I think it's worth looking into using the whole Chevy unit, except for the Dodge output shaft and the tailhousing. Both Chevy and Dodge tailhousings bolt on with a 4-bolt pattern. The obstacle is that they are offset from each other. Since they don't line up, the oil passage from the pump will not be connected (bad). To reindex it should require nothing more than drilling and tapping four new holes and possibly filling the old ones. I still have a Dodge back case and Chevy tailshaft in my garage (the opposite scenario), so maybe I could look into this more. If it would work, the conversion could be done without any welding.
     
  9. thebigdaddyof2

    thebigdaddyof2 1/2 ton status

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    Do you believe that the Dodge case would be clocked up too far to be usable?

    Keep us informed about the Chevy rear case mod investigation.
     
  10. Blue85

    Blue85 Troll Premium Member

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    From what I've seen, Ford and Dodge cases are clocked similarly, but the Chevy is about 90 degrees off from that. It's easy to imagine how 90* in either direction would be impossible or unuseable. It could still work with one of those clocking rings, though.

    I looked at the Chevy case closer and where the 4 bolts go in that connect the tail shaft to the main housing, there is extra material cast for the threads. You would have to weld in bungs to take the threads or use some kind of a press-through stud. Except for where extra material was designed in, these cases are very thin. I'm pretty sure redrilling the tailhousing is impossible.
     
  11. Blue85

    Blue85 Troll Premium Member

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    To do the mod, you need the following:

    1) Good Chevy 208 (or needed rebuild parts)
    2) Dodge 208 case
    3) Your desired output yoke + matching seal.
    4) New driveshaft with slip yoke in it.
    5) Dodge speedometer gear for your application.

    You need the following parts from the Dodge case (everything else in it can be junk):
    -Back half of the case
    -Tailhousing
    -Rear output shaft (also called mainshaft).

    Other than the cases, the input shaft and the output shaft, all of the internal parts are interchangeable between the Chevy and Dodge cases.

    The back half of the Dodge case needs three modifications:
    1) The fill plug should be relocated higher to match up with the Chevy (note in the pictures that my case has 3 plugs now. The middle one never needs to be removed. It is the stock Dodge fill plug.) You could skip this and fill the case through the vent tube or by pulling the yoke off, but it would be inconvenient.
    2) Threaded insert for T-case to bellhousing support rod. If you don't care about this rod, you could skip this one.
    3) Weld in a bung to accept the shift rod. The Chevy and Dodge cases have their shift rods clocked differently around the mainshaft inside the case. You have to add another "Chevy-style" one to the inside of the Doge back case. There is really no way around this modification. [​IMG] [​IMG]
     
  12. Blue85

    Blue85 Troll Premium Member

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    About yokes,
    As far as I can tell, all Dodge NP208 cases used rear yokes with 1.4" major diamter, 2" deep 32-splines. The half ton cases come with a lousy 1310 yoke (shown below). This is smaller than the 1330 stuff that Blazers come stock with. Here are the Spicer yokes that will fit:
    1310 CV yoke #2-4-5341
    1330 CV yoke # 2-4-5441
    1330 non-CV yoke # 2-4-5521
    1350 non-cv yoke # 3-4-6211
    1410 non-cv yoke # 3-4-10951-1

    Non-CV yokes require National Seal #473204 (larger i.d.)

    About speedometers:
    Most cases seem to have a 13-tooth speedo drive gear. I don't know what other drive gears are available, but driven gears are available at least in 25-32 tooth. The speedometer cable exits to the driver's side, in contrast with the Chevy which exits to the passenger's side. I was able to re-route the stock cable to make it hook up. I have not been able to confirm whether or not they are the same as Jeep speedometer gears.
    [​IMG]
     

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