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1984 K-5 with a vibration...(STILL)

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by RMA, Dec 7, 2002.

  1. RMA

    RMA Newbie

    Joined:
    Nov 21, 2002
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    Location:
    Upstate New York
    '84 K-5, NP-208C, 700R4, 305, 3.73 posi, 42,000 miles,
    Stock suspension.

    My last posting told of a vibration that was speed related not RMP related. Starts about 30 MPH and peaks about 42. Worse under load. Goes away and comes back about 55 and stays. I have had it to 75 and the vibration is still there.
    <font color="red"> New Data </font color>

    Starting about 55 MPH if you were to very lightly hold the throttle to maintain speed, there is a very loud roaring noise that goes away when load is put on the driveline either by more speed or backing off. This noise sounds like you were driving on the rumble strips along interstate highways.

    What has taken place thus far...

    Put the truck in 4WH and pulled the rear drive shaft to find the vibration gone. Replaced u-joints, no change. Changed drive shaft with another used shaft, no change. Took both drive shafts to a shop that balances and found both to be defective and not repairable. Purchased a new drive shaft only to find the vibration worse at all speed ranges. Put wedges between the springs and differential housing to point the pinion higher (4 degrees) and found the higher end vibration much better. Lower end vibration still strong. Pulled the differential out and found nothing abnormal. All internal bearings and gears are good as well as the axles.

    Dear tell, what is left. The transfer case? Is there anything in the transfer case that can cause this type of vibration? I have located a '90 Blazer that was rolled with the NP-241. Will it replace the NP-208?

    Again, thanks for all past replies and I look forward to any help that may be available. RMA rabrams@albany.net


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  2. YtseJam

    YtseJam 1/2 ton status

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    Hmm, did you rotate the tires to see if the pitch or range of the vibration wouold change? Sounds to me like possibly a carrier bearing.
     
  3. DPI

    DPI 1/2 ton status

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    Location:
    In the Burbs close to Tulsa, OK
    I would by an angle guage from harborfreight.com or sears sells them. Your angle at the driveshaft yoke and the angle of the pinion yoke need to be the same. If your rear springs are settled, that may have thrown the angles out. I would pull the torque converter inspection cover and check your flywheel to torque converter bolts too. The two cases are about the same, however, you will need a new driveshaft yoke to fit the 241. I would just get the one with the case if you buy it. You may want to go with a slip yoke eliminator and a 1350 CV like I did. But I really don't think you need it with no lift. I am running 9" of lift and have no drivetrain vibration, except from the Swampers...

    [​IMG]
     
  4. 75-K5

    75-K5 3/4 ton status

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    Location:
    Anderson, Indiana
    I'm going to agree with carrier bearing. The same thing happened on our '68 C20. Same speed-related vibration that felt about the way you were describing it. Give it a try, it's not a very expensive fix and it doesn't take much time (unless you had to beat it off with a 12 pound sledge like we did /forums/images/graemlins/smile.gif)
     
  5. Thumper

    Thumper 1/2 ton status

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    You said you angled the pinion higher... well its not just a matter of raising the pinion higher. You have to measure the angle at the top, and make the pinion angle the same. Maybe you are too high in the back.
    Also, when the driveshaft is off, and the rear wheels off the ground is there any play in the pinion itself up and down? When you rotate it slightly how much backlash is there?

    Id probably guess its your pinion angle tho. You may have to flip the shims around to drop the front of the pinion.
    Mike
     

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