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NP208 + Lift +stock driveshaft = problem

Discussion in 'Trucks and Trailers' started by DwarF, Jan 6, 2001.

  1. DwarF

    DwarF LawnSite Member
    Posts: 30

    Hola,
    I was excited to find such a great forum with actual helpful advice! =) I was searching the old transfer case discussions, and didn't see anything about the NP208, so I thought I would start a new thread.

    I have an '83 K5. I was experiencing some mild knocking with the stock suspension on it, but like the impatient person I am, I lifted it 4", and put some 35" BFGs on it. Needless to say the knocking got worse, but it is not the U-joints, I am sure of that. Likewise, it doesn't appear to be the slide yoke on the NP208, it is tight as well. But, the yoke has slid out quite a bit due to the lift, and I think that it is slid out past it's comfort zone, and that is causing the knocking. *it only knocks in 1st when you get on the gas from a standstill* In any case, I think I could solve this with a slightly longer driveshaft. Also it has the stock driveshaft that has the cruddy injection molded plastic pins to hold the endcaps on the U-joints, so I would like to just dump the whole driveshaft. That said, I would like to switch to a splicer style for the extra travel now that it is lifted. This will not jive with the NP208's slide yoke (I don't think), so now, after lots of jibberish...here is my question.

    Can I just change out the yoke and/or tailhosing on the NP208 and get it to not slide? Do I have to replace the whole transfer case and go to a different model? If so, Should I go back to a NP205 or is there better aluminum options now? I want the "slide" to be in the driveshaft, not in the yoke/transfer case, to give me a straighter line to the rear diff. I also want to be able to lose the rearend and still get home with the front power, but I definitely don't need full time 4wd.

    Gracias in advance
     
  2. TLS

    TLS LawnSite Fanatic
    Posts: 7,940

    Just a question, is the knock engine RPM related or speed related?

     
  3. DwarF

    DwarF LawnSite Member
    Posts: 30

    Well, to be completely honest, there are two vibrations. If I get on the gas from a standstill, there is a prominent knocking right where the transfer case is. If I don't stand on the gas, it doesn't do it. So I would say it is speed related, if I am even going 10 mph, and I stand on the gas, it will not do it. When it switches into second, it shimmys too, but nearly as bad, it is just a vibration in second. The vibration in first is like I ran over grandma and she is knocking on the floorboard!
     
  4. TLS

    TLS LawnSite Fanatic
    Posts: 7,940

    Sounds like your flexplate. When they crack, they make a big rackett. Put your foot on the brake, and give it 1/2 throttle. Does it make the noise while the truck stays still?

    4" lift doesn't usually require driveshaft work, but who knows.

     
  5. DwarF

    DwarF LawnSite Member
    Posts: 30

    Rock - DwarF - Hard Place

    To answer you flatly, no it didn't make the "same" racket. But if I let it move just a tad, it did make the same racket, only like a little knock, not a full on power knock *by a tad,I mean > 1 mph*. Maybe if you told me what a flexplate was, I could look to see for sure. are you talking about the undercarriage rock-guard for the transfer case that bolts onto the frame crossmember?
     
  6. TLS

    TLS LawnSite Fanatic
    Posts: 7,940

    The "flexplate" is your flywheel in an automatic transmission equipped vehicle. It is a thin sheetmetal disc with a gear around the perimeter for starter motor engagement. Often the around the torque converter or crankshaft bolts, stress fractures turn into major cracks that, upon heavy torque (major acceleration) flex upon themselves and create the loud rackett we are referring to. If you stand on brake and give throttle (lots) this will occur without movement of vehicle. It also happens whenever you pull out (accelerate).

    Also check motor mounts (front) and rear (transfercase) for movement. It may be your cooling fan hitting your fan shroud. Or could be your output shaft bearings in your transfer case, or your slip yoke.

     
  7. DwarF

    DwarF LawnSite Member
    Posts: 30

    Wow, that narrows it down =), but seriously. This knocking I am referring to, sounds quite litterally like a hard physical knock on the floorboard, right between the center console and the passenger seat. It is strong enough to stir change around in the center console. I first thought it was the shaft bearings in the tcase, but it is pretty solid, very minimal movement. I have to shake the bejesus out of it to get it to move at all *and it is very little*. I am sure it is not the cooling fan, I have heard that before. You may be right on the flexplate, but that sounds pretty difficult to figure out without disassembly, but it is in the same area of question. Do you know of any aftermarket slip yoke eliminator kits?
     
  8. TLS

    TLS LawnSite Fanatic
    Posts: 7,940

    Do the stand on brake and GAS at same time test. This will determine this matter real fast.

     
  9. DwarF

    DwarF LawnSite Member
    Posts: 30

    I did before the previous two responses, sorry if I wasn't clear. It doesn't knock if I stand on the breaks and the gas together. If it should be obvious, it wasn't. If it should be subtle, I may have missed it but I listened carefully and didn't hear or feel anything close to the knocking upon acceleration from standstill.
     
  10. TLS

    TLS LawnSite Fanatic
    Posts: 7,940

    Sorry, this rules out flexplate. May be gear or bearing damage in trans or transfer case. Remember, if noise is truck movement related, shift into (transfer case N-neutral) and give gas or see if knock goes away. Another test is to remove rear driveshaft and engage 4WD and drive around in front wheel drive. Caution, dont ROMP on it with just a front driveshaft, but see if noise is still present.

    All else fails, turn up radio!!! Life is simple!!!

     

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