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Back end thumpty bumpty noise

Discussion in 'Lifted & Offroad Suspension' started by torqydd, Jul 26, 2011.

  1. torqydd

    torqydd Rockstar

    I am completely stumped on this one. I have a odd every day thump bump from back end of truck. I have taken out my spare, hitch tightened everything from shocks to u bolts and is still there. It only does it at slow speeds well at least that is the only time i can hear it. Driving down the alley and pulling in and out of angled driveways. It is almost the same noise when as you would get when shaking the truck side to side. Now my rear shackles do squeak and squawk under various loads but don't really see those making the thump bump noise.

    I have installed lift blocks and front level kit and thats its.
    2008 chevy x cab z71
  2. stephan

    stephan Rockstar 4 Years 5000 Posts

    I'd disconnect each of the rear shocks just to make sure one of them isn't broken. It's hard to tell they're broken when bolted at both ends, except for an odd noise. If they're both good, I'd next check to make sure both your rear blocks are seated on the locating pins. Barring that, then I'd just continue checking the torque on all your bolts cuz something is still loose. Did this noise start after you put in your rear blocks, or was it there before? Also what did you torque your U bolts to??
  3. torqydd

    torqydd Rockstar

    if this double posts im sorry i hit the post button but nothing happened. Stephan it did start after the block install...Ill get back under it tonight and check the shocks but now on the block being set right while it be obvious or is it something the jack needs to come out to do. Just by looking at them the appear to be sitting flat against everything. On the torque specs I went with what gm said said for factory bolts which was 74 or 80 have to look back at my sheet. If aftermarket ones are supposed to be higher do you know what that number might be?
  4. stephan

    stephan Rockstar 4 Years 5000 Posts

    Since this noise started after the block install, I'd check them first. They may look like they're seated ok, but one or both could be sliding around. Look for a shiny spot or for any place where rust or dirt has been moved (indicating foreward or rearward movement of the axel/block etc). As for torque, unless they came with larger diameter U bolts, the torque should be the same, but I would definitely put the torque wrench to them & check that they are tight. If you find nothing wrong there, then procede with checking the shocks. Did your block kit come with longer shocks or shock extensions? Do you feel the shocks topping out? This would be most noticeable on driveway aprons & slow up & down movement of the rear of the truck, rather than on sharp short bumps like potholes. It would feel like the rear of the truck is moving upward like normal & then would suddenly come to an abrupt stop. If it was doing this for long then it would eventually break the shock(s)
  5. torqydd

    torqydd Rockstar

    well just got out from under the truck and one side was loose but when i went to retighten them i guess dirt or something got the treads messed up ended up having to cut one of them off. So I used my brand news I just got in that where waiting on 3" blocks instead of the 2.5" one I have now. so got to use my new ones. went through the whole process again and I even turned the base plate completely around just incase i put it back on the first time backwards or something. Retorque both sides to 80lbs and test drive and stupid thump bump was still there, so completely lost . then went to shocks took both off checked and nothing seems busted no leakage still function normal in my opinion.

    With my 2.5" block I didnt need new shocks or extenders according to what I was told and when I sat the truck down on its wait I still have almost 3 inches I had to push back up to get it in its resting spot which was not fun at all. But with the 3" i know I will have to get longer one or the extenders.

    The only thing I did notice is just how close the treads are to the axle housing on both sides and that the passenger side the u bolt closest to the front is **** eyed and the rear one is ever so slightly but the drives side is square. Something is still going on i am assuming on the passenger side just havent found it. As soon as I get another free moment Ill try and figure out how to load some pics up and let you see what I see.

    Maybe time to give up and take it to the shop and see what they will charge me to figure it out
  6. stephan

    stephan Rockstar 4 Years 5000 Posts

    Is it possible that with the lift that your U joint angle is so severe that the joint is hitting on the yoke now? I know that a lot of the guys have been going with the angled blocks to try & keep DS angle closer to stock. Look for shiny spots around the inside of the yoke to see if it's been rubbing. Put your jack stands under the axle so you can rotate the drive shaft by hand & see just how close it comes. Then imagine going over a driveway apron & imagine how much closer it's going to be because this is going to make it closer than when sitting at static height. Does this popping thumping seem to be speed related (as in: going in a driveway faster, the thump is also faster, like it is related to drive shaft speed?)

    *Before you take it to a shop I'd try & find this yourself, cuz a shop is going to charge you straight labor for all their time invested & they might not be able to find it, but you're still out $$$.
    Last edited: Jul 27, 2011
  7. torqydd

    torqydd Rockstar

    Soon as wifey gets home and takes over baby watching I will have to get back under there and look. The only time i here is creeping in and out of the driveway or any other inclined entrance where I am having to turn into or out of. Cause what I am running now is a flat top block. To describe the noise better you would have to go out to your truck and stand on either side grab the the bedside and push back and forth left to right, which is almost the exact same sound it makes. Now stupid question since I have been out the truck scene for a while the new blocks I ordered are 3" tapered does the taper go towards the front or rear? I know I should probably know.
  8. stephan

    stephan Rockstar 4 Years 5000 Posts

    Describing it that way almost sounds like you have too much axle side play. When you have it up in the air, grab the sides of the tires & pull them in & out & check it. They will move some, but not a lot. Still doesn't make sense though, because if it's too much side play, you should only hear it one time during the turn (when it actually shifts over) rather than a repetitive thump thump. The thin part of the block goes towards the front of the truck. This is to try & re-establish the original DS angle so it is not so severe after it's lifted. Thinner at the front, tilts the front of the 3rd member up to minimize DS angle & less wear & tear on the U joint.
  9. torqydd

    torqydd Rockstar

    I knew what I was trying to say but couldn't get the words out axle end play. which would mean having to break into the pumpkin to find out that one. I had wife drive it down the alley with me in bed and then did the side to side push method and I have to say it is the same noise. hmmm may actually get to use my extended warranty for something and I am due for rear end service at well, two birds with one stone maybe but still need to make sure its not something I have done first. Dont like hearing its because you did so and so and now its doing this random thing.
  10. torqydd

    torqydd Rockstar

    Well for anyone having the same issue with a odd thump/thud noise coming from the back end. I gave up trying to hunt it down and took it to the dealership. What they found was that the left leaf spring where is mounts to the frame bracket had cracked/come apart and when the truck shifted the bolts running though it was metal on metal. I guess you cant see this when mounted cause I looked and looked and couldn't visually see anything wrong, but if anyone ever comes across this it may be something you want to check out.

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