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Mystery clunk?

Discussion in 'Chevy Trucks' started by swa136, Feb 2, 2007.

  1. swa136

    swa136 Senior Member
    Messages: 149

    When I accelerate from a stop I get a thud that feels just like a broken motor mount. It doesn't happen in reverse. I've checked both mounts, transfer case mount, and they're fine. Anybody ever experience this? It's a 2001 GMC 1500, 4.8 w/ 4L60E 78,000 mi. Any ideas would be appreciated as this is driving me crazy.
  2. lawnmedic

    lawnmedic Senior Member
    Messages: 703

    Make sure that the slip yoke is lubed. Suspension movement when taking off will cause a slight movement in the yoke, If it cannot move freely, it may cause a clunking noise.
  3. dlcs

    dlcs 2000 Club Member
    Messages: 2,160

    My wifes 2001 Chevy 1500 4x4 did the same thing after about 2 years. I think it made it to the dealer about 10 times for that problem. They never could find anything wrong with it, they even tore down the transmission. I kept on them so much that they had a regional service manager come down from Detroit and he said it was normal. B.S. I threatened lawsuit and they gave her a 100,000 mile warranty on the drivetrain. We ended up trading it in, not long after that. There is a service bulitan out on it and it basically says to do nothing.:rolleyes:
  4. jbwerling

    jbwerling Junior Member
    Messages: 27

    swa136, Does it feel like its coming from the rear end? I have an 03, and it feels like something is shifting in the drive train somewhere. I was wondering if it was a rear u-joint.
  5. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    swa136, I posted this before but here it is again.... GM bulletin.....Clunk, Bump or Squawk when Vehicle Comes to Complete Stop or Accelerating from Complete Stop (Replace Rear Drive Shaft Nickel-Plated Slip Yoke) #01-04-17-004 - (Oct 5, 2004)
    Clunk, Bump or Squawk when Vehicle Comes to Complete Stop or Accelerating from Complete Stop (Replace Rear Drive Shaft Nickel-Plated Slip Yoke )
    1999-2002 Chevrolet and GMC Extended Cab Short Box Pickup Models (Silverado and Sierra)

    with 4L60-E (RPO M30) or 4L80-E (RPO MT1) Automatic Transmission and Automatic 4WD (RPO NP8)

    Some customers may comment on a clunk, bump or squawk noise when the vehicle comes to a stop or when accelerating from a complete stop.

    A slip/stick condition between the transfer case output shaft and the drive shaft slip yoke may cause this condition.

    Replace the rear drive shaft slip yoke with a new nickel plated slip yoke, P/N 12477702 (1500 Series) or 12477704 (2500 Series).
  6. swa136

    swa136 Senior Member
    Messages: 149

    jbwerling: It feels like the rubber to rubber thud you get from a broken motor mount after the motor torques up, then sets back down on the frame. I think B&B's post might explain it, but I have reg. cab w/ long bed, and the TSB is for ext. cab w/ short bed(can't see where there'd be a difference). This started about 500 miles after I changed the 2 U- joints on the rear shaft, so I'm gonna go with B&B's recommendation, and change that slip yoke, and see what happens. Thanks for the input guys! I'll post the results after I change it.
  7. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Don't worry about the TSB only covering the e-cab/short bed truck, as changing the yoke AND using the special GM grease to lube the spline's on the new yoke will fix the thump in any truck whether it's a reg cab or an extended cab/short bed as long as it's a one piece drive shaft and not a two piece with a carrier bearing. ;)
    Last edited: Feb 3, 2007