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  • exhaust rattle?

    unfortunately Ive gone over a stupidly high speed bump in an industrial park near my work and hit the bottom of the car as the front wheels went over.

    since then i have had a rattle mostly around 2.5k rpm or as i come of the throttle and let the car engine brake. it gets better and worse as it pleases.

    Ive given the car to my mechanic and although he said he can see where the exhaust has been hit at the front there is nothing loose and no air gaps in the actual exhaust. he has been under the car whist its running and seems to think it might actually be inside the exhaust.

    has anyone had this before? or have any ideas?

    i can believe how unnecessarily high the speed bumps are in this particular place, i was only crawling :(

    i want the car ready for Gaydon on Sunday so any help would be great.

  • #2
    I guess you could have dislodged a baffle inside slightly..rip em apart and strip the baffles out!

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    • #3
      what will it do to the exhaust if i rip the baffles out? are the baffles not in the boxes? my mechanic doesnt think its coming from the boxes he said its coming from the front?

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      • #4
        A damaged CAT?
        2002 '52 S54 - Titanium Silver with 18" BBS LMs, AP Racing BBK, KW V3, H&R anti roll bars & ACS flippers (previously 2000 'X' S50 - Arctic Silver)

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        • #5
          I hit my exhaust when it grounded out heavily, there is a bracket sort of under the driver's footwell area that had broken off. I think I re-welded it on (would need the undertray removing to see it if I recall correctly.

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          • #6
            Here are some pics of the back box modification I did for my silencers :
            https://v2tre.wordpress.com/2015/06/...lusta-loppuun/

            Sorry for the finnish language in my blog but you get the idea of the internals of the boxes from the pics. First picture shows the unmodified internals.

            These silencers have a truly robust (stainless) structure and it would take a really significant impact before any of the internals would turn loose. They have double sheet skin structure and all internal parts are thick metal welded tightly into place.

            The middle (twin) part of the exhaust contains the catalysers which instead of the typical ceramic inserts found in family cars are metal cat "race" type. However, a moderate to strong hit into these might be able to get the internals to become loose and vibrating.

            At one point, I had an irritating resonance coming beneath the car and after much looking it finally proved to be the broken front exhaust support beneath the gearbox. Part number 9 here http://bmwfans.info/parts-catalog/Z3..._lambda_probe/

            The support had broken clean into two pieces but when looked quickly, the "seam" was so clean that is was not easily visible. Only after heavily moving the exhaust back and forth I noticed that the support bracket was actually in two pieces the ends rubbing each other. The sound seemed to come from the back even if the problem was in the front.

            Hopefully this helps.

            PS/EDIT : The bracket is the same that mentioned by C_W just minutes ago :) Worth to check, it is a cheap and an easy fix.
            Last edited by JuhaV; 11-08-2015, 11:56 AM.
            The older I get, the faster I was ...
            BMW HP2 Sport
            ex- BMW Z3 M Coupe - Cosmosschwartz Metallic

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            • #7
              thanks guys

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              • #8
                Originally posted by c_w View Post
                I hit my exhaust when it grounded out heavily, there is a bracket sort of under the driver's footwell area that had broken off. I think I re-welded it on (would need the undertray removing to see it if I recall correctly.
                This.

                I had the exact same rattle on falling revs and just needed this bracket re-fixing.

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                • #9
                  Originally posted by c_w View Post
                  I hit my exhaust when it grounded out heavily, there is a bracket sort of under the driver's footwell area that had broken off. I think I re-welded it on (would need the undertray removing to see it if I recall correctly.
                  Originally posted by alanw89 View Post
                  This.

                  I had the exact same rattle on falling revs and just needed this bracket re-fixing.

                  Is it the bracket that hangs from the gearbox that causes the problems?

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                  • #10
                    On mine it was the bracket holding the exhaust, the shape of two humps with the bolt in the centre.

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                    • #11
                      Yes, that's it - one of the lowest parts on the car as it's a bit further back that the front wheel it can catch ground easily.

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                      • #12
                        indeed it ended up being the bracket, thank you guys

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