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Vibration at half throttle (long)

Discussion in 'The Garage' started by Chris_T, Dec 24, 2002.

  1. Chris_T

    Chris_T 1/2 ton status

    Joined:
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    Location:
    Saskatoon, SK
    I have an odd vibration in my 72 K5. It occurs when I'm coming off the gas and the truck starts to coast. It seems to happen at any speed, but is more noticable on the highway. At higher speed it's accompanied by a rattle that is transmitted through the driveline (can feel it in the T-case shifter).

    This one appeared out of nowhere. I put in a 700R4/205 (adaptor shaft) and it was OK. Later I lifted it an extra few inces (now with 8" skyjackers to cure the butt-sag and match the front 6" lift) and had new driveshafts made - still no vibration. I had an odd sound coming from the truck a bit later and it turned out to be a loose T-case output yoke (nut worked itself loose) - tightened it up and no noise. Then changed to 4.56 from 3.73s. Drove fine for a short while then the new vibe just appeared. It's quite annoying since it's most prevalent when you come up behind someone on the highway and ease off the gas and it will vibrate until the truck has slowed down and it's under load again.

    Going to crawl under it after Christmas and check things out. Going to check:

    Torque convertor to flexplate bolts
    Torque convertor cover
    T-case and axle yokes
    Driveshaft and U-joints

    I read a post somewhere that carrier bearings can cause a vibe. The only things I can think of that might cause this after the gear swap are 1) the axle wasn't set up properly and the bearings have since worn, but I trust the guys at the shop where I had it done; or 2) the increased driveshaft rpms with the gear swap have exagerated an existing vibe, causing U-joints to fail or something to work itself free.

    It's tempting to just put a double-cardan rear shaft on there and see if that fixes things, but I won't have time to get one made before I drive from Alberta to Missouri.

    Does this problem sound familiar to anyone or can you suggest something else to check once I get the air out of the tires and the garage warmed up to crawl under there?

    Thanks in advance,

    Chris
     
  2. Chris_T

    Chris_T 1/2 ton status

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    No one?
     
  3. Sandman

    Sandman 3/4 ton status Author

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    My old truck did this right before the rearend blew. Was fine cruising and speeding up but vibrated you to death when letting off the gas. Maybe take at look at that.
     
  4. SkulzNBonz

    SkulzNBonz 1/2 ton status

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    Location:
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    Sounds an awful lot like a u joint.

    John
     

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