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Driveshaft angle causing vibration at speed?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Stoopalini, Oct 30, 2002.

  1. Stoopalini

    Stoopalini 1/2 ton status

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    I've been battling a vibration issue for a while now, and think maybe I've got it tracked down. I have an '84 blazer, 2 1/2" ORD shackle flip, 14 B FF, running 33" tires.

    The vib used to happen during acceleration, deceleration, and just about all the time. Recently, I swapped out the U-bolts and spring plates for 1 ton (I was running 1 ton u-bolts on 1/2 ton plates) and I lowered the T-case using the 1" spacers.

    The vibrations have almost gone away now. It is smooth during acceleration and deceleration, but I get a pretty bad whirling around 55mph and above. When I say 'whirling', I mean it is a vibration that comes and goes in time; Almost like a bearing would feel.

    If I'm doing 60mph, and I shift into neutral, the vib is still present but it becomes constant instead of cycling. When I shift back into drive, it starts the cycling again.

    Looking at my drive shaft angles, the drive shaft is almost straight in line with the pinion and has a pretty good angle up at the T-case. Would this cause what I am describing? and if so, do I need to shim the rear to bring the pinion down some?

    Thanks for any advice,
    Thomas.
     
  2. imiceman44

    imiceman44 1 ton status

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    Do you have a CV on the rear shaft?
    If not then you got the wrong setup.
    When you have a CV you line up the drive shaft with the pinion and point it to the CV, but if you don't have it, you should have the pinion parallel (within 2 degrees) with the output on your T-case.
    That would definitely make a Vibration the way you have it. /forums/images/graemlins/smile.gif
     
  3. Stoopalini

    Stoopalini 1/2 ton status

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    No, I have the stock drive shaft. So do all 14B FF axles point the pinion up to the T-case, or were my perches moved?

    I was going to bring the drive shaft into the shop and have them weld a 1350 yoke on and balance it ... thinking that maybe it's out of balance. But if the pinion pointing upwards is causing my problem, can I shim the rear to bring it down some?

    Thanks for the info,
    Thomas.
     
  4. Muley

    Muley 1/2 ton status

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    Do you have a slip yoke on the drive shaft? If so check the splines to make sure they are not crap.
     
  5. Stoopalini

    Stoopalini 1/2 ton status

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    There is a slip yoke into the NP208 t-case, but not one in the middle of the driveshaft.
     
  6. imiceman44

    imiceman44 1 ton status

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    Yes you SHOULD shim the rear to bring it down. It might be easier than turning the pads.
    Also check the slip yoke in the T-Case, grab it and try shaking it up and down if there is movement then you have a problem if not just turn down your pinion.
    Yes the 14bolts usually are on long trucks, longer than the K5 at least and they used a 2 piece drive shaft with a bearing support in the middle so the pinion would be pointing up.
     
  7. Stoopalini

    Stoopalini 1/2 ton status

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    Ok, great! Thanks for the info.

    Do you know if anyone sells a shim that will also provide 1" of lift? Like the ORD 1" zero rate add a leafs with an angled cut?

    Might as well lift the rear another 1" if I'm going to be putting in shims anyway ....

    Thanks again,
    Thomas.
     
  8. drivelineman

    drivelineman 1/2 ton status

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    you need a c/v joint at the t-case - what your feeling is called gear rattle- Jess
     
  9. Stoopalini

    Stoopalini 1/2 ton status

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    I thought about that too, but couldn't find a C/V setup for the NP208 that wouldn't break my bank.

    Do you offer a C/V setup that'll work with the NP208 and my stock shaft? If so, I would love to know the price of it?

    Thomas.
     
  10. drivelineman

    drivelineman 1/2 ton status

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    449.00- its all one ton- Jess
     
  11. Stoopalini

    Stoopalini 1/2 ton status

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    Does that price include the whole shaft, from t-case to pinion?

    If it does, would just your slip yoke with the CV mate to my stock shaft with a conversion joint?

    [​IMG]

    Thomas.
     
  12. drivelineman

    drivelineman 1/2 ton status

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    its complete unless you want the 1 ton at the diff its 56.00 for that yoke-Jess
     
  13. Stoopalini

    Stoopalini 1/2 ton status

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    I'm only running 33" tires right now, and eventually plan to go to 35" with a whole lot of fender cutting (maybe add the 1" zero rates), so I don't really need the complete 1 Ton setup.

    Sounds like your slip yoke with the C/V joint is perfect for me. I'll be giving you a call in the morning.

    Thanks Jess,
    Thomas.
     
  14. drivelineman

    drivelineman 1/2 ton status

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    its got a one year waranty too-Jess
     
  15. Stoopalini

    Stoopalini 1/2 ton status

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    Alright, well I had my driveshaft lengthened about 1 1/2", 1350 yoke welded on, all new U-joints, and it was balanced.

    I still have the vibration /forums/images/graemlins/mad.gif I took the Blazer down to the drive train shop, and they measured the angles at 6' and 7'. He said those are perfect, and my vib isn't due to a driveline angle issue. He said the most likely cause is a blown out NP208 output bushing, and I should try replacing it. He said the driveshaft being too short could have put too much stress on it and ruined it.

    Does this sound reasonable? Is there anything else I should do to my t-case when I repalced the bushing and seal?

    This vib is really starting to drive me nuts. It's like a mission now, I won't quit until it's smooth! /forums/images/graemlins/wink.gif

    Thomas.
     
  16. TX Mudder

    TX Mudder 1/2 ton status

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    </font><blockquote><font class="small">In reply to:</font><hr />
    Do you know if anyone sells a shim that will also provide 1" of lift? Like the ORD 1" zero rate add a leafs with an angled cut?


    [/ QUOTE ]

    Try this guy:
    Custom leaf spring shims

    I haven't bought from him, but I'm planning to. I need to measure what angle i need first.
    -- Mike
     
  17. Stoopalini

    Stoopalini 1/2 ton status

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    Thanks for the link. Looks like he has a pretty good setup going on. But it seems my angles are ok (6' and 7'), so I really don't need to shim the rear yet. Once I get this vib issue resolved, I am going to lift the t-case back up and then I'll most likely need the shims.

    Thanks,
    Thomas.
     
  18. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Which was 6 and which was 7? That is a static measurement. While driving (especially accelerating and decelerating, or maintaining higher speeds), the pinion will rotate up and down. Up while acclerating or mainting high speeds, and down when decelerating. A 1 degree difference can become a 3-4 degree difference pretty quick. I don't know if you have covered this, but making sure the driveshaft is perfectly balanced (may want to take it to a different shop to balance just to see), and the tires and brakes are all set. I have even heard of a slightly bent axle shaft causing vibration that was hard to diagnose.
     

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