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loud "thud" from driveshaft?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by personaltrainer, Feb 17, 2005.

  1. personaltrainer

    personaltrainer 1/2 ton status

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    Okay. took the truck to my mech to get it looked at b/c I was at a loss for answers. He drove it and said that it sounds/feels like any other lifted K5 he's ever driven or owned (and he's owned 2). He said it's the chain in the transfer case that has slop in it and the only thing to do to fix it is to rebuild the t-case and he said it's not garanteed that a rebuild will fix it. He also said that the driveshaft could be lengthened a little but it's not gonna stop the noise/feeling either and it's not worth it.

    here's the situation - when taking off from a stop the truck makes a "thud" sound. this happens after my foot leaves the brake pedal and befor i get to the gas pedal.

    WTF? Please give me any ideas that ya'll have. i know we all have lifted K5s and I can not seem to find much info on this problem so it leads me to believe that it's not THAT common. thanks:confused:
     
  2. surpip

    surpip 1 ton status

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    In 2wd? humm dosent make any sence to me, i dont see how the chain could affect how it drives in 2wd, i think your Mech. friend dosen't know as much as he thinks he dose. Mine had a 6in lift on it and there is no "thud" i would go under your truck and grab the drive line and see if you can feel any slop in it, it sounds more like a bad u-joint to me.

    tranny t case? what do you have?
     
  3. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Do you have a locker ? Most have a little backlash , and the driveshaft turns a little before it locks and turns carrier . Just a thought . I get some thuds once in awhile and its been fine :dunno:
     
  4. rcpilot

    rcpilot 1/2 ton status

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    Do you have lift blocks??? If so ya could be gettin axle wrap.. mine did that until I got rid of the blocks...
     
  5. spearchucker

    spearchucker 1/2 ton status

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    It could be one of two things, but without actually feeling the type of thud I couldn't tell you. The first is if you have a slip yoke then it could be binding under acceleration/decceleration and when too much pressure builds up it suddenly slips and give a loud bang. You can try greasing the slip yoke but the noise will return after a few weeks. The other possible problem could be the gears in the rear axle are going out. If you have large tires with the stock axle and many miles on it then the axle is probably going out. Have you taken the diff cover off to see if there're any metal flakes inside?
     
  6. personaltrainer

    personaltrainer 1/2 ton status

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    I'm thinking it sounds more like the axel warp scenario OR the gears going out. Seems to be more external (like driveshaft) than inside of the rear end.

    Yes it's up on blocks in the rear. should i switch to springs and see if that fixes it? What's the first step here? I'll remove the diff cover to look for flakes - if that looks clear, and i think it will, then should i go ahead and remove blocks and go with a "real" lift? If i do this will the slip yoke still be binding or should that take care of it?
    Thanks again.
     
  7. rcpilot

    rcpilot 1/2 ton status

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    I removed my blocks and installed a shackle flip.. did'nt need shims at all...thump/bang went away... flex like crazy now!!!
     
  8. Hossbaby50

    Hossbaby50 3/4 ton status

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    What year is the truck and what transfer case? A tcase chain should have nothing to do with an thuds you here as long as you are in 2wd.

    My guesses. Driveshaft ujonts, pinion nut loosening up, gear slop in the rearend, or axlewrap. Also check your tranny mount.

    Harley
     
  9. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    I used to get a little thud when leaving from a stop as well. It ended up being a lose TC crossmember that allowed everything to torque back and forth a smidge. Get under the truck and take a close look at all your mounting brackets. You may need a prybar to help simulate the changing loads experienced when leaving a stop......
     
  10. personaltrainer

    personaltrainer 1/2 ton status

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    not even sure what t-case i have (i live in the city and rarely even get a chance to go wheelin) but I'll run all this by my mech. Not sure that he'll admit he's wrong though. looks like it's time to find a new mech?


    This sucks. Thanks for all of the input.
     
  11. personaltrainer

    personaltrainer 1/2 ton status

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    anyone got any suggestions on the "softest" rear springs around for a reasonable price? Looking at pricing these so I know what I'm getting into..

    keep in mind that I'm mostly riding around town on these things with the occational hunting trip. thanks.
     
  12. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Maybe check your motor mounts as well....?

    I've got a "clunk" when I pull the gear selector into reverse. I've had a locker in the rear for a long time, but the noise is newer.

    Other suggestions of u-joints, etc were also suggested to me to resolve mine.


    Good Luck.
     
  13. personaltrainer

    personaltrainer 1/2 ton status

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    thanks gregg. looks likt the stereo install is gonna have to wait - 1st things 1st.

    I'll give the motor mounts a look as well. Thanks man.
     
  14. gone huntin

    gone huntin 1/2 ton status Premium Member

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    My Suburban started doing the same thing a couple of weeks ago BEFORE I put the lift on. I traced it down to the driveshaft yoke. I removed the driveshaft and greased the splines in the slip yoke where it slides into the t-case and all was well, no more clunk. My 2wd Dodge did this and I took it to the dealer to have it checked out under warranty. It was the same problem and they put a special type of grease on the splines that is still there today, and that was four years ago, still no clunk. I'm gonna go by there and see what kinda grease it was.
     
  15. personaltrainer

    personaltrainer 1/2 ton status

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    If you could get the details that would be great. My mech and i decided after looking it over that the answer is either gonna be - a bar welded to teh axel and then to teh frame to keep the thing form wrapping OR some springs int eh rear to eliminate the blocks. That's our starting place. I hope i don't spend the money on this only to find that the problem could have been fixed with a little grease!!
     
  16. fatbob

    fatbob 1/2 ton status

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    You said "this happens after my foot leaves the brake pedal and befor i get to the gas pedal. "

    Axle wrap will occur AFTER you get on the gas and the torque twists the springs. So while getting rid of the blocks would be an improvement, I dont believe it will solve the orginal problem. I would go with greasing the yokes, checking mounts [tranny/tcase], and also the brakes. Since this occurs AFTER you let off the brakes but BEFORE you give it gas, it could be the rear brakessticking a little.
    .02
    Bob
     
  17. personaltrainer

    personaltrainer 1/2 ton status

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    I originally though it was the rear brake sticking too. That was so many "theories" ago that I forgot to investigate it. would that still make the driveshaft "jar" like it does? I can see and hear that the noise is def. coming from the driveshaft.
     
  18. personaltrainer

    personaltrainer 1/2 ton status

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    also the rear output shaft of the driveshaft has been leaking, I replaced the seal and it STILL leaks - does this clue help any?
     
  19. red77blazer

    red77blazer Registered Member

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    Technician A says:

    i had a problem sounding very much like you have, and i went through every thought everybody has mentioned here.i would accelerate and then brake right as the torque would change as i'd bring my foot over to the gas it would make a semi loud noise almost like a bang or clunk, hard to describe, i ran 2wd and had a 203 tcase, i wen't back and forth with different ideas and 3 months later had the trans case rebuilt and it never did it again, i would be cautious. I'm not saying its your t-case, i've heard noises that sound similar to mine be something totally different, but i would say before you spend a bunch of money, i would either a)wait for it to get worse till you can figure it out (which is not desirable because it could cause other problems), or B)get several people and some 4x4 specialists to listen, i found it was the t-case by having the truck put on a dyno, not one for horsepower but just one for testing. Just a suggestion.
     
  20. red77blazer

    red77blazer Registered Member

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    Technician A says:

    I just read that- do you mean the rear output seal on the transfer case or the rear diff pinion seal? (the seal behind the flange that the driveshaft goes to on the rear axle)
    If it was the diff- did the noise happen before- if it started after the seal replacement its possible the crush sleeve got crushed too much which would cause your seal to go out again, grab the rear yoke on the diff and move it up and down if it moves thats your problem, or try rocking the truck back and forth in part watching the rear yoke, if it moves in/out or up/down at all when it rocks off the parking pawl thats your problem,
    If it was the t-case- then do the same with the t-case yoke, move it up and down if there is play there you go.

    But the seal no matter which one it was may be a clue, a seal will go out over and over again if the bearing behind it is bad, and seals usually start leaking for that reason.

    So exactly which seal was it?

    another thought is if your truck is lifted and the driveline angle is incorrect it could cause vibrations that could eventually take out the seals/bearings.

    so more info would be helpful.
     

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