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NP208 + Lift +stock driveshaft = problem

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

  1. DwarF

    DwarF Junior Member
    Messages: 15

    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 PlowSite.com Addict
    Messages: 1,425

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

    DwarF Junior Member
    Messages: 15

    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 PlowSite.com Addict
    Messages: 1,425

    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 Junior Member
    Messages: 15

    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 PlowSite.com Addict
    Messages: 1,425

    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 Junior Member
    Messages: 15

    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 PlowSite.com Addict
    Messages: 1,425

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

    DwarF Junior Member
    Messages: 15

    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 PlowSite.com Addict
    Messages: 1,425

    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!!!
     
  11. DwarF

    DwarF Junior Member
    Messages: 15

    Slip yoke, I can't drive around in front wheel only. That is part of my complaint. But I will try switching around in the tcase and see what happens, thanks for your effort. I am sure I am going to find the answer to this one cold night in the middle of no-where! But I will fill you guys in when I know what it is.
     
  12. DwarF

    DwarF Junior Member
    Messages: 15

    Cool,
    I think your hints are correct, and my assumption about the slip yoke is wrong. Tell me what you think:

    It knocks bad in 2Hi from a take off from standstill, as we have discussed.

    In 4Hi, it still knocks a little bit. But it is later in the gear, and not nearly as severe, one to three knocks top on full throttle.

    In N (on tcase) there are no knocks what-so-ever. Takes off.

    Same for 4Lo

    So you think this is bearing damage in tcase?
     
  13. beerandcope

    beerandcope Junior Member
    Messages: 27

    i am having the same kind of trouble you are haveing and i foun that the bearings were bad on th front drive shaft even though i couldnt move the plate. you might wanna try that even though you might not think it is that.
     
  14. mike reeh

    mike reeh Senior Member
    Messages: 114

    Hmm.. Interesting..

    I have a similar problem, only different. :) I have a 203 case (with part time kit) and I have to always either A) drive with the hubs locked or B) drive with hubs unlocked, in 4wheel.. In other words the Front driveshaft has to be spinning the same rpm as the rear, or it creates a really bad knock. With the front hubs locked, if I peel out on dirt or something, it still does it because they are turning diff speeds.. It sounds sort of like a gear barely engaging, trying to grab.

    Is that at all similar to your problem? I know we have totally different transfer cases but its worth a shot.

    Im a little confused as to what you mean by Transfer case in NEUTRAL and Takes off.

    mike
     
  15. TLS

    TLS PlowSite.com Addict
    Messages: 1,425

    Maybe he means, takes off in the driveway while in park! Been there done that!

    DwarF,

    Another thing to check that can make your noise. Look closely at all of your exhaust system. My 75 Sub has exhaust exits 1/4" below the running boards. When I get on it, they vibrate like heck and rattle the whole truck. Was scratching my head for a few days on this one.
     
  16. DwarF

    DwarF Junior Member
    Messages: 15

    I promised I would come back and tell you the solutions. Well, it was two things.
    1. The Tcase mounts or transmission mounts if you are looking them up in a parts catalogue, were worn too rubbery, so I bought some new polyurathane (sp?) ones, and that solved 90% of it.
    2. The driveshaft is at a bit of a severe angle due to the slip yoke, and I need to get a Spicer type, and slip yoke eliminator.

    So, if you are experiencing the same problem, the mounts cost only 45 bucks, and fixed 90% of the problem!