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driveshaft

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Bhintz, May 5, 2003.

  1. Bhintz

    Bhintz 1/2 ton status

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    I just got a 4 inch susp. lift last week I love it but I now have a vibration in my driveshaft but today I had a load in the rear which lowered the rear susp. about 2 inches and the vibration stopped. This mean my driveshaft is to short and I need a longer one? I was told that with a 4 inch lift I would need a new driveshaft I guess thats not true. My next question is I will be dropping in a 14 bolt ff in a month or so when I do this will it compensate for the now to short driveshaft b/c the the 14 bolt is bigger than the 10 bolt and push the drive shaft back enough to stop the vibration? /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif
     
  2. heavy4x4

    heavy4x4 1/2 ton status

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    The vibration isn't a result of the driveshaft being too short, it's the increased angle of operation that the lift creates. When you loaded up the back with weight, it squatted down a bit and corrected the angle. Did you "drop your t-case" when you installed the lift (put spacers between frame and crossmember)?
     
  3. Bhintz

    Bhintz 1/2 ton status

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    I didnt drop the t-case I was thinking about doing that, how much would that cost?
     
  4. TxK5Blazer

    TxK5Blazer 1/2 ton status

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    correct me if i am wrong but just move the spacers from outside the crossmember to between the crossmember and the frame right. Does that hurt your engine mounts though?
     
  5. BLZN4FN

    BLZN4FN 1/2 ton status

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    I 2nd the spacer thing. I droped the T-case on one of me other K5's drove it for 2 years no problems with motor mounts ect..
    The K5 I have know I put degree shims in the spring packs to get the corect pinion angle.
     
  6. txbartman

    txbartman 1/2 ton status

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    82 is correct. I am assuming you have a NP208 tcase. To drop it, simply move the spacers from the top of the bolts (inside the frame rails) to go between the frame rail and the crossmember. Be sure to have a jack supporting the crossmember when you do this. The crossmember is what is supporting the back of the engine, the tranny and the tcase.

    Another probably cause of the vibration is the fixed driveshaft with the slip yoke. With a 4" lift, dropped tcase and stock shaft, mine had a periodic vibration at highway speeds. Nothing too annoying, but it was definitely there. Part of this has to do with the design of a slip yoke shaft. It all has to do with the angles. The only way to completely remove the vibration is by establishing the proper angle and then maintaining it throughout the suspension's movement. With a fixed-length shaft, that is practically impossible. As the rear axle moves up (suspension compresses), the slip yoke slides in which changes the angle. Same holds true for when the suspension droops. If you replace they shaft with a telescoping one with a double cardan (CV) joint at the tcase-end, then the angle stays much more true. As the suspension moves up and down, the shaft absorbs the movement in a telescoping action. But since the joints themselves do not move much (if at all), the angles stay much more true. That is why you very seldom have driveline vibration problems on fixed output transfer cases.

    If I were you, I would drop the tcase and live with it for now. Then, when you swap in your 14BFF, replace the driveshaft with one from High Angle (Jesse) or Tom Woods Driveshafts. I have the latter and am very pleased. This will serve multiple purposes. (1) you can get a CV shaft that will eliminate your driveline vibes and (2) it will allow you to get the proper pinion-end on the shaft so you don't have to run a funky combo u-joint.

    Hope this helps.
     

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