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Why is NP 208 weak

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by blazinzuk, Jan 6, 2004.

  1. blazinzuk

    blazinzuk Buzzbox voodoo Premium Member GMOTM Winner

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    Just wondering why the NP 208 is a weak t-case what parts usually break etc. It looks like that is what I will be using in my blazer
     
  2. TrcksR4ME

    TrcksR4ME 1/2 ton status

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    I think most problems are related to its aluminum case. It is also a chain drive instead of all gear like a np 205. Other than that I dunno...
     
  3. TXsizeK5

    TXsizeK5 1/2 ton status

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    THe way the internals are setup is structurally weaker than the 241. if you go chain drive alluminum case, go 241
     
  4. 4GUNZ4X4Z

    4GUNZ4X4Z 1/2 ton status

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    [ QUOTE ]
    I think most problems are related to its aluminum case. It is also a chain drive instead of all gear like a np 205. Other than that I dunno...

    [/ QUOTE ]

    Thats it in a nutshell. I've grenaded 2 208's, once while rock crawling and once while hill climbing. The aluminum is not all that strong. I do like the low gear in a 208, but the weakness of the case itself doesn't even out. Who knows, you might have a 208 that will out last your truck, I guess it just depends on how hard you wheel. I guess what I'm getting at is if you put any serious power into a 208 your looking for problems, if you wheel lightly then you will probably be good to go.
     
  5. txbartman

    txbartman 1/2 ton status

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    The onoly two weak points of the 208 are: (1) the aluminum case and (2) the slip yoke rear output. Yes, it is chain driven, but you will be hard-pressed to EVER find ANYONE that has had a chain fail on them. The chains fail about as often as gears in a 205 or 203. The aluminum case is a severe weak point. I have seen one of these crack climbing a ledge on a fairly basic trail before. The slip yoke is "weak" simply due to the fact that it is a slip yoke.
     
  6. 4wood

    4wood 1/2 ton status

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    So what's the best slip yolk eliminator to fix this "weak" point? (sorry for arrogating the post)
     
  7. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    [ QUOTE ]

    I've grenaded 2 208's, once while rock crawling and once while hill climbing.

    [/ QUOTE ]
    You shouldn't have been rock crawling with a 208. /forums/images/graemlins/shocked.gif


    you said it yourself[ QUOTE ]
    The aluminum is not all that strong.

    [/ QUOTE ]
     
  8. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    I would definantly go with a 241 instead of a 208. The 241 is a stronger sturdier case. The oiling system is also much better in the 241 and the low range is a little lower at 2.72:1 compared to the 2.62:1 208. I have a 241 swapped into my 85' in place of the old 208. You wan't to find an 89' 241 because it will have a mechanical speedo and swap directly into place without any modifications. /forums/images/graemlins/thumb.gif
     
  9. HarryH3

    HarryH3 1 ton status Author

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    I think the biggest weakness of any case with the slip yoke output design is when you combine the slip yoke with a lot of suspension lift. The slip yoke will take plenty of abuse with stock suspension because the slip motion is nearly linear with the output shaft due to the small angle of the driveshaft. Start lifting the suspension and the output shaft sees more side loading as you get higher. Add a huge side load to the binding of the splines under load and then compress the suspension suddenly... BANG! The case explodes. /forums/images/graemlins/eek.gif /forums/images/graemlins/frown.gif I'd bet that a 208 or 241 converted to a non-slip yoke would take a lot more abuse on a lifted rig. /forums/images/graemlins/thumb.gif
     
  10. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    [ QUOTE ]
    Start lifting the suspension and the output shaft sees more side loading as you get higher. Add a huge side load to the binding of the splines under load and then compress the suspension suddenly... BANG! The case explodes. /forums/images/graemlins/eek.gif /forums/images/graemlins/frown.gif

    [/ QUOTE ]

    Hmm, maybe I should have done the SYE when I rebuilt my 241. /forums/images/graemlins/thinking.gif
    [hyjack] Do you think 7" of lift is a lot for a slip yoke?[/hyjack]
     
  11. R72K5

    R72K5 Banned

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    [ QUOTE ]
    I would definantly go with a 241 instead of a 208. The 241 is a stronger sturdier case. The oiling system is also much better in the 241 and the low range is a little lower at 2.72:1 compared to the 2.62:1 208. I have a 241 swapped into my 85' in place of the old 208. You wan't to find an 89' 241 because it will have a mechanical speedo and swap directly into place without any modifications. /forums/images/graemlins/thumb.gif

    [/ QUOTE ]

    really ? so if i came across an 89 241 with 32 spline then it would swap right in place of my 208 in 83 with 465 ? what about adapter and outputs ?
     
  12. HarryH3

    HarryH3 1 ton status Author

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    [ QUOTE ]
    [hyjack] Do you think 7" of lift is a lot for a slip yoke?[/hyjack]

    [/ QUOTE ]
    That's getting up there! Take a look under your rig and imagine what kind of side load would be on the output shaft if you pressed straight forward on the rear of the driveshaft. The steeper the angle, the higher side loading is going to be. /forums/images/graemlins/frown.gif
     
  13. 4GUNZ4X4Z

    4GUNZ4X4Z 1/2 ton status

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    [ QUOTE ]
    [ QUOTE ]

    I've grenaded 2 208's, once while rock crawling and once while hill climbing.

    [/ QUOTE ]
    You shouldn't have been rock crawling with a 208. /forums/images/graemlins/shocked.gif


    you said it yourself[ QUOTE ]
    The aluminum is not all that strong.

    [/ QUOTE ]

    [/ QUOTE ]

    It was back in the days when I was 20 or so and I thought I knew everything. It was definitly a first hand learning experience that gave me some knowledge of why/where/how/when a 208 is weak. /forums/images/graemlins/thumb.gif
     
  14. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    [ QUOTE ]
    really ? so if i came across an 89 241 with 32 spline then it would swap right in place of my 208 in 83 with 465 ? what about adapter and outputs ?

    [/ QUOTE ]
    hmm, I'm not to sure on the 465, I was refering to an automatic.
    I know with mine the 208 and 241 adapters are the same behind the th700 and so are the splines with I think 85' and later.

    If I had to guess I would say that if the the splines are the same on both the donor 241 and the 208 then it will work and I would guess that the adapters are the same also. /forums/images/graemlins/thinking.gif
     
  15. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    [ QUOTE ]
    I think the biggest weakness of any case with the slip yoke output design is when you combine the slip yoke with a lot of suspension lift. The slip yoke will take plenty of abuse with stock suspension because the slip motion is nearly linear with the output shaft due to the small angle of the driveshaft. Start lifting the suspension and the output shaft sees more side loading as you get higher. Add a huge side load to the binding of the splines under load and then compress the suspension suddenly... BANG! The case explodes. /forums/images/graemlins/eek.gif /forums/images/graemlins/frown.gif I'd bet that a 208 or 241 converted to a non-slip yoke would take a lot more abuse on a lifted rig. /forums/images/graemlins/thumb.gif

    [/ QUOTE ]

    Ya want a 208 that looks like this one /forums/images/graemlins/thumb.gif
    [​IMG]
    [​IMG]
    [​IMG]
     
  16. mr_fujisawa

    mr_fujisawa 1/2 ton status

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    what about a 208 with a skid plate for those rocky situations?
    (not to highjack this too)
     
  17. blazinzuk

    blazinzuk Buzzbox voodoo Premium Member GMOTM Winner

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    I am using the 208 because it is what I have I don't think I will have enough power to break the case. To whoever has broken the case did it break because you hit a rock or did it just split from torque input. I am very carefull when I wheel as I run 38s with a 10bolt frontend /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif
     
  18. 4GUNZ4X4Z

    4GUNZ4X4Z 1/2 ton status

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    [ QUOTE ]
    what about a 208 with a skid plate for those rocky situations?
    (not to highjack this too)

    [/ QUOTE ]

    I had a skid plate under my 208's and I still have the same one under my 203. I haven't really givin any thought about a rock busting a 208, seems reasonable though.
     
  19. juanblzer

    juanblzer 1/2 ton status

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    I've been seriously abusing my 208 and 700r4 combo for some time now (since 95') to be exact. I run a medium duty Goodwrench crate motor that moves pretty well. I'm currently running a built 700r4 built in 02'. I have a great skidplate combo. I've never smacked the t-case itself. I've been told that it's a weak case by two tranny/t-case builders. I was also told that the chains don't really stretch and they are decent if you take care of them. I don't take care of mine other than armoring its mount (custom crossmember). I have an extra 208 ready to go in if this one craps it's pants... but I'm slowly starting to look in the direction of an atlas or maybe a doubler. (P.s. I don't have kids so I save my nickels and dimes for every new addition to my baby truggy).
     
  20. txbartman

    txbartman 1/2 ton status

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    [ QUOTE ]
    So what's the best slip yolk eliminator to fix this "weak" point? (sorry for arrogating the post)

    [/ QUOTE ]

    There really isn't an acceptable SYE for the 208. Some driveshaft shops sell a kit. This kit is essentially a new yoke that slips over the output splines of the 208 and bolts to the shaft. This requires drilling and tapping the output shaft; not an easy task. Then you use a telescoping driveshaft.

    Another alternative is to use a CV telescoping driveshaft with the slip yoke. When doing so, 99% of the movement of the slip yoke on the output shaft is eliminated. The suspension movement is absorbed by the telescoping driveshaft and the double cardan joints. This setup also helps to eliminate driveline vibrations caused by altering the stock geometry. If you are going to stick with a 208, I would recommend such a setup.

    A skid plate will help protect the case of the 208. I have never seen one split from torque. I have only seen a case split from sitting the truck on a rock (direct impact - resolved by skid plate) or from allowing the suspension to compress enough that the slip yoke jams into the tcase (resolved by CV driveshaft).

    At that point, the only other "weakness" is that if you loose your driveshaft (broken u-joint, busted axle, etc), the slip yoke will come out of the back of the tcase. That exit will soon be followed by fluid! No slip yoke = no tcase plug!

    Hope this info helps ya!
     

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