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Bad vibration! Help!

Discussion in 'Chevy C/K Truck Forum' started by airmanhalef16, May 2, 2013.

  1. airmanhalef16

    airmanhalef16 New Member

    Good evening,
    I am hoping that you all can help point me in the right direction. I have a 1984 GMC k1500 that I bought three years ago and have been working on. I am almost complete with the mechanical side of things except for this irritating vibration. It seems to originate from the rear. you can actually look back and see my truck vibrating. It seems to occur at around 55+ being worse between 55-60. Things that have been done that had no effect- New tires, new (used but new to the truck) wheels, new shocks, and new u joints. I have taken the truck in to have the tires/wheels rechecked and they were fine. Anyone have any other ideas as to what it could be? I have been reading.. does this sound like a bad pinion gear or axle shaft? I am at a loss and I would really like to be able to drive on the interstate with out rattling my brains out and definitely would like to fix it before I invest in painting the truck. Thanks for any advice, tips, tricks, and things to check!
  2. Pikey

    Pikey Moderator Staff Member 3 Years ROTM Winner 1000 Posts

    I would jack the rear end up and put some jack stand under it, block the front tires. Then, have someone get in it and put it in gear and let off of the brake. Get behind it and watch the tires spin. See if they spin true. You may have a bent axle shaft.
  3. airmanhalef16

    airmanhalef16 New Member

    Thanks! I will give that a try Saturday!
  4. Pikey

    Pikey Moderator Staff Member 3 Years ROTM Winner 1000 Posts

    I have a few more questions. when you did the ujoints where you able to move them easily by hand after install? I once had a friend "help" me and bend a ear on my driveshaft. It made the joint tight and it vibrated. Also, check the straps that hold the ujoints on the rear pinion yoke. I had one crack while reinstalling a driveshaft and the truck shook like crazy around 60mph. Above 60 was fine. take a pry bar and see if you can move the ujoints in the rear pinion yoke. When my strap broke the vibration hogged out the hole, even after replacing the strap the ujoint moved. I had to install a new yoke. While it is up and spinning check out the driveshaft, see if you see it vibrating.
  5. airmanhalef16

    airmanhalef16 New Member

    I want to thank everyone for all of the quick and helpful responses. I checked my ujoints ect and they were all good. I jacked up my truck and checked the rear tires and the right one "wobbled" so I am assuming I have a bad right rear axle shaft. I tore the old shaft out tonight (it looks fine but there was a def wobble). This brings me to another question. I opened up the differential to take out my axle shaft and found a few other things possibly wrong. The four internal gears ( the two side gears and the two smaller ones above and below the pin) all had teeth with chips in them. They were not bad enough to have whole teeth missing but there were numerous areas that were chipped. Could this cause my vibration? I am going to replace the axle shaft anyways so I guess it would be a good idea to replace those gears right? I inspected the pinion and ring gear and they looked great. Does anyone know any good places to get the internal gear set? Oreilly seems to be the only store carrying it for 162.. lmc has them but with shipping its the same price. Anyone else have an idea where to find them?

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