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Boot floor / Sub-frame / Diff mount failure thread

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  • Originally posted by Dave P View Post
    Does the title of this thread need to be updated? any suggestions for something more descriptive
    Tweaked the title slightly

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    • See post in "Good or ad dealer section" re boot floor repairs in the Midlands.

      Don't worry, it needn't be terminal for your MC or cost a fortune to put right!

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      • Interesting site regarding subframe,


        https://www.bmwfabric.com/post/trunkfloor

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        • Originally posted by Dave P View Post
          Interesting site regarding subframe,


          https://www.bmwfabric.com/post/trunkfloor
          Nice articulation, makes sense. Some other interesting refurb threads on that site too
          1998 ///M Coupe

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          • Great article! The Gif is really good at explaining.

            I'm soon to re fit my subframe with polybushes, standard diff mount bush, near diff ear and strengthened floor that should be the end of it!

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            • Can anyone recommend garages who've repaired the boot floor please?

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              • Does this look okay?
                Last edited by sonu_anand; 20-01-2021, 10:25 PM.

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                • It's a little hard to tell in those photos.

                  At the bottom of the first photo are those spot welds all good? I think not? They are on the angled bit? Can't see properly though so please don't panic :)

                  Unfortunately to really tell you have to remove the stuck on bitumen sound deadening which is a right pain.

                  Mine looked ok with the deadeing in, but when I removed it I could see the spot welds starting to fail. Some photos on my journal thread if you want to see.

                  It doesn't look bad in the photos but hard to see. Is the diff ear all good? I'd check there as another indication :)
                  Last edited by urquattrogus; 25-09-2020, 10:13 AM.

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                  • Originally posted by urquattrogus View Post
                    It's a little hard to tell in those photos.

                    At the bottom of the first photo are those spot welds all good? I think not? They are on the angled bit? Can't see properly though so please don't panic :)

                    Unfortunately to really tell you have to remove the stuck on bitumen sound deadening which is a right pain.

                    Mine looked ok with the deadeing in, but when I removed it I could see the spot welds starting to fail. Some photos on my journal thread if you want to see.

                    It doesn't look bad in the photos but hard to see. Is the diff ear all good? I'd check there as another indication :)
                    Ahh, thanks. Any tips on removing the bitumen?

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                    • Originally posted by sonu_anand View Post
                      Ahh, thanks. Any tips on removing the bitumen?
                      A heat gun, and a few metal scrapers or a wallpaper scraper. Try and peel it off in sheets as much as you can and with some due swearing.

                      There is also seam sealer on the straight edges to the sides and or the corners which may have to be scraped off for further investigation.

                      Or if you are a smart alec supposedly you can get some dry ice and it will come right off almost in one!!! :) (videos can be found on youtube)

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                      • thanks.

                        How do I check the diff ear?
                        Need to get under the car?

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                        • Yup, sometimes they crack on the edge of the ear or worse where the ear bracket is welded to the crossmember.

                          https://www.z3mcoupe.com/forum/showt...t=20799&page=4

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                          • Originally posted by urquattrogus View Post
                            Yup, sometimes they crack on the edge of the ear or worse where the ear bracket is welded to the crossmember.

                            https://www.z3mcoupe.com/forum/showt...t=20799&page=4
                            thanks, very helpful

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                            • The only way to check as said is to remove that patch of sound deadening, under here you'll find the usual suspect spot welds. Worse failures are down the left chassis rail that runs front to back from the boot, but you would know about that.

                              On my car I had a light creak from the boot when setting off, but nothing apparent looking in side or underneath, but under the *sound deadening patch* there were a few cracked welds. Nothing major but flood-welded them and plated the area, and also doubled up the diff ear bracket.
                              Last edited by c_w; 26-09-2020, 01:40 PM.

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                              • Originally posted by c_w View Post
                                The only way to check as said is to remove that patch of sound deadening, under here you'll find the usual suspect spot welds. Worse failures are down the left chassis rail that runs front to back from the boot, but you would know about that.

                                On my car I had a light creak from the boot when setting off, but nothing apparent looking in side or underneath, but under the boot there were a few crack welds. Nothing major but flood-welded them and plated the area, and also doubled up the diff ear bracket.
                                thanks c_w

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