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Thump, thud sound from rear - only at take off, even low speeds.

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    #1

    Thump, thud sound from rear - only at take off, even low speeds.

    I hear a thump sound when I take of from 0 miles an hour. Even at parking lot speeds. But if I am coasting at 30, 40, or even 80, and accelerate in the powerband, I dont here it. It is weird. I dont think it is the rear bushings or suspension because everything is basically new. VERY NEW. New rear subframe bushings, new trailing arm bushins, new shocks, new springs, new CSB, etc.

    The problem happened after I did some work to the car and the car slipped off a jack stand. A popping noise happened but when I inspected any damages, all I could find was that the exhaust was off one hanger, and there was a small hole made in the exhaust piping. That made me think that the stand only affected the exhaust and muffler. So that is what makes me think it is the muffler.

    HOWEVER! I took my muffler to a shop to have a new one put in (I needed it anyway), and I still hear the same noise. Could it be the exhaust still, or something in the suspension/ driveline.
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    #2
    A thumping noise, especially if it becomes worse with acceleration in the lowest gears, is usually a failure of the rubber mount of center support bearing. Which in turn is almost always a result of binding or bad drive shaft u-joints. The only long term fix is a new or rebuilt drive shaft.
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

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      #3
      It however only happens at take off. If I am coasting at speeds higher than 25mph I dont hear it - Even if I punch it in the powerband of a gear.

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        #4
        It sounds like your center support bearing rubber has failed. What you describe are the symptoms of that.
        -Andy

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          #5
          Originally posted by dashboardmonkey View Post
          It sounds like your center support bearing rubber has failed. What you describe are the symptoms of that.
          +3, its not what you want to hear but, this guy and JLevie have already answered your question.
          @IRON-E30 aka Edwin:D

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            #6
            Originally posted by graphikg View Post
            It however only happens at take off. If I am coasting at speeds higher than 25mph I dont hear it - Even if I punch it in the powerband of a gear.
            If the earliest stages, the noise from the drive shaft will only be evident in first or reverse when proceeding from a stop. When greatest torque is on the drive shaft. But it will get worse.

            Get the car up in the air and take a look at the rubber mount of the center support bearing. If torn the drive shaft is the problem.
            The car makes it possible, but the driver makes it happen.
            Jim Levie, Huntsville, AL

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              #7
              I had exactly the same issue, mine was ancient subframe bushings. Even though yours are new, you shoulkd take a close look at them, make sure they are well-seated.

              If anything, you need to look at the CSB and the diff mount, right?

              GL!
              Luke

              Closing SOON!
              "LAST CHANCE FOR G.A.S." DEAL IS ON NOW

              Luke AT germanaudiospecialties DOT com or text 425-761-6450, or for quickest answers, call me at the shop 360-669-0398

              Thanks for 10 years of fun!

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                #8
                Glad I read this because my car's has the same symptoms. I'll have to check it out in the spring...
                sigpic

                Buy and sell your E30s and E30 parts on E30 Marketplace!

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                  #9
                  I was thinking subframe bushings. CSB is possible as well.

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                    #10
                    Ok - so this problem definitely happened when the car was completely lifted on four stands and I took it off improperly. DARN! I heard a loud sound that that is what it was.

                    How long can I drive on it like this? Long enough for me to get the part in?

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                      #11
                      Ok. I lifted the rear of the car and spun the wheels. Even with shifts and movement of Te d-shaft, it has no noise. That's what's making think it is the subframe bushings. Something may have shifted when improperly dropping the car from stands. Plus, the problem doesn't get worse at higher speeds.

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                        #12
                        Originally posted by graphikg View Post
                        Ok. I lifted the rear of the car and spun the wheels. Even with shifts and movement of Te d-shaft, it has no noise. That's what's making think it is the subframe bushings. Something may have shifted when improperly dropping the car from stands. Plus, the problem doesn't get worse at higher speeds.
                        Take a look at the rubber mount of the center support bearing. If it has tears in it you have likely found the cause of the noise. Bad u-joints and a failed center support bearing, at least initially, won't make noise when the rear wheels are in the air and spinning as very little torque is being applied to the drive shaft.

                        That said, there could be other problems in the rear suspension. By this time the rear trailing arm bushings, subframe bushings, and differential mount are way overdue for replacement just from age. And check to make sure that the bolts that mount the differential are tight.
                        The car makes it possible, but the driver makes it happen.
                        Jim Levie, Huntsville, AL

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                          #13
                          Dropped the exhaust and the CSB looks okay. It looks as new as when I installed it about 10 months ago. As I also said, the subframe and trailing arm bushings are also polyurethane new.

                          I am starting to think it is the exhaust banging back there. I think this because 1) it only happens going forward and I dont hear the "thump" going in reverse, and 2) the noise only started happening when I improperly dropped my car from the jack stands. I think one of the stands slanted when lowering the car and pushed on the exhaust which is why there was a hole created on the exhaust and it came off one of the rubber hangers.

                          I think the thumping is the exhaust. I cant find any other culprit.

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                            #14
                            Did some more investigating. It is definitely not the exhaust. I am getting kinda stumped.

                            It only happens at take off, even within the 5 MPH range. It does not happen during higher speeds even when punching on and off the throttle at higher speeds.

                            It could be my Polyurethane subframe bushings. OR... it could be something in the driveline behind the CSB. I checked the CSB and everything there looks fine.

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                              #15
                              Is your differential installed securely to your subframe? I've had the bolts loosen slightly, and it caused a "clunk" in first gear.

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