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Goofy vibe @ 50mph... rear is bouncing

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by KRAZIE87K5, Jul 6, 2002.

  1. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    Just got done redoing the rear suspension. I installed BorregoK5's bolt-in shackle flip, ORD's Zero Rates, and moved the axle back 1.5". The drive shafts were cut to the correct length. I also have installed a 465/205 (FIXED YOKE) combo, which I traded for my 400/205.

    Cruising at speed, the truck starts jumping or hopping. Not violently or anything, just enough to make everything inside bounce a bit. /forums/images/icons/smirk.gif If I keep the speed </= 50mph, the vibe is not present.

    The truck prior to this recent batch of mods could cruise all the way up to 90! So what happened? Suggestions? /forums/images/icons/grin.gif

    -Dan
     
  2. BorregoK5

    BorregoK5 1/2 ton status

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    If you put your hand on the tcase shifter as you accellerate you can usually feel harmonic vibrations in the drivetrain as they progress to the point of annoyance. Did you get a new crossmember or adapt the old one? Did you shim the rear pinion back down or are you running a CV shaft now?
     
  3. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    The crossmember had to be changed to the "flat" type, which I already had and I used the Energy Susp. poly mount.

    The rear shaft is NOT a CV, I didn't have the $500 to drop for one! /forums/images/icons/frown.gif /forums/images/icons/tongue.gif So I have a new shaft with 1350 joints, and a slip.

    And I have not shimmed the pinion back down. I installed the Zero Rates, and the shackle flip, that's it. Can I install shims AND the Zero Rates? /forums/images/icons/confused.gif

    So the bouncing I feel is probably a vibe in the rear drive train? Always wondered what that felt like... NOW I KNOW! What degree shims should I order? I've heard you suggest 4* or 6* shims to to others. Will that work for me?

    Thanks!

    -Dan
     
  4. BorregoK5

    BorregoK5 1/2 ton status

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    Yeah, I'd guess thats driveline vibration all right given the other things you've done. The zero rates get added to the leaf pack so I don't see why you couldn't run shims as well. With the shims it is a bit harder to align the spring pack as the set pin height is reduced so keep your U-Bolts tight after install. Every rig's lift is different but between 4-6 degrees sounds right. I shimmed my 14b back down 6 degrees after having the spring perches rotated for a 6 inch lift spring which I never bought but rather went the shackle flip route. You might try a 6 first to get it below parallel just a hair. Let me know how that works out, Brian Wise (Bozowise) is doing the same thing, you might PM him and see where he's at with this as well..
     

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