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  • #31
    too right.

    you should be the first port of call if it happens to someone else :shock:

    Comment


    • #32
      Can someone give me a link to the various fixes that people have devised to strengthen the subrame/floor /diff mount, where there are photos of the hardware for the fixes. I've seen something before, but can't remember where, and a search on this just pulls out loads of stuff to wade through.
      /// Exdos ///
      "Men who try the impossible and fail spectacularly are infinitely superior to those who reach for nothing and succeed" --Napoleon Bonapart

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      • #33
        try here :!:

        http://www.z3bimmer.com/Garage/Fixes/
        Ex 'V3RY M - MCoupe track monster'
        New toys

        Porsche widebody project

        Cayenne Diesel

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        • #34
          Lee,

          Cheers :!: Exactly what I was looking for 8)
          /// Exdos ///
          "Men who try the impossible and fail spectacularly are infinitely superior to those who reach for nothing and succeed" --Napoleon Bonapart

          Comment


          • #35
            I also found this link to the Randy Forbes fix. There are loads of photos of how Randy does this fix by following the three links given in Randy's post (the 6th posting in the thread).

            This guy comes from the same school of over-engineering that I subscribe to rather than the Colin Chapman school of under-engineering. :wink:
            /// Exdos ///
            "Men who try the impossible and fail spectacularly are infinitely superior to those who reach for nothing and succeed" --Napoleon Bonapart

            Comment


            • #36
              Exdos.

              In terms of preventative measures for this defect?

              Any ideas?

              If it ain't broke, dont fix it, but it looks like a weakness that I would like to mitigate :shock:

              Comment


              • #37
                Originally posted by Rags
                Exdos.

                In terms of preventative measures for this defect?

                Any ideas?

                If it ain't broke, dont fix it, but it looks like a weakness that I would like to mitigate :shock:
                I think I'll be inclined to take the same "if it ain't broke" attitude. I'll take a good look again at mine sometime soon to see if the potential weakness can be strengthened a little more simply than the Randy Forbes fix, because his fix is a lot of work for a preventive measure.

                I think that part of the problem of the floor and diff mounts failing might probably lie in movement of the subframe on their bushes, especailly when these things get worn. I've had a butt strut on my MC for 2 years now and I think that this part may well be a sufficiently preventive measure in keeping the parts of the back end which are supposed to be rigid, fixed together. There was one guy at Gaydon yesterday who'd made his own butt-strut and bodybrace for his MR which I liked. I shall probably make something similar myself. The beauty of the butt-strut and body brace is that they are "bolt on" parts and so you are not having to weld onto your car. If you did the Randy Forbes fix as a preventive measure, would someone coming to examine your car not think your car has already suffered from the dreaded floor failure :?:

                I hope you managed to get home OK with that spare wheel.
                /// Exdos ///
                "Men who try the impossible and fail spectacularly are infinitely superior to those who reach for nothing and succeed" --Napoleon Bonapart

                Comment


                • #38
                  you could also order polyurethane rear subframe bushings to cope with the movement. i ordered some from ireland engineering and will get them installed to try to minimise movement of the subframe.

                  Comment


                  • #39
                    Originally posted by exdos
                    Originally posted by Rags
                    Exdos.

                    In terms of preventative measures for this defect?

                    Any ideas?

                    If it ain't broke, dont fix it, but it looks like a weakness that I would like to mitigate :shock:
                    I think I'll be inclined to take the same "if it ain't broke" attitude. I'll take a good look again at mine sometime soon to see if the potential weakness can be strengthened a little more simply than the Randy Forbes fix, because his fix is a lot of work for a preventive measure.

                    I think that part of the problem of the floor and diff mounts failing might probably lie in movement of the subframe on their bushes, especailly when these things get worn. I've had a butt strut on my MC for 2 years now and I think that this part may well be a sufficiently preventive measure in keeping the parts of the back end which are supposed to be rigid, fixed together. There was one guy at Gaydon yesterday who'd made his own butt-strut and bodybrace for his MR which I liked. I shall probably make something similar myself. The beauty of the butt-strut and body brace is that they are "bolt on" parts and so you are not having to weld onto your car. If you did the Randy Forbes fix as a preventive measure, would someone coming to examine your car not think your car has already suffered from the dreaded floor failure :?:

                    I hope you managed to get home OK with that spare wheel.

                    Well, I got home ok but not with that wheel!

                    That new wheel didn't have a tyre valve.

                    So we swapped the valves over, and fitted the wheel.

                    But it didn't clear the strut!!


                    So I resorted to using the tyre foam and limped back at 60mph and the tyre(even this morning) is still inflated

                    Anyway, time to buy some new tyres as the tyre foam allegedly eats the tyre from the inside!

                    Comment


                    • #40
                      I'm not sure if the butt strut will add any strength to the parts that are known to fail as they are quite a bit further backward, at the diff/boot floor area. I think its quite easy to see why its possible for the rear mounting parts and structure of these cars to fail, given that over 300bhp is being pushed through brackets that look like they'd normally be used for interior trim mounting points. I think the double ear diff mounting would relieve and distribute the loading a lot better.

                      Apparently some of the brakcets can be "doubled up" which would add a lot of strength then weld the brackets better to the body rather than spot-welding.

                      Comment


                      • #41
                        Originally posted by c_w
                        I'm not sure if the butt strut will add any strength to the parts that are known to fail as they are quite a bit further backward, at the diff/boot floor area. I think its quite easy to see why its possible for the rear mounting parts and structure of these cars to fail, given that over 300bhp is being pushed through brackets that look like they'd normally be used for interior trim mounting points. I think the double ear diff mounting would relieve and distribute the loading a lot better.

                        Apparently some of the brakcets can be "doubled up" which would add a lot of strength then weld the brackets better to the body rather than spot-welding.
                        c_w,

                        Here's a diagram I've done to show the main parts on the back end and how any movement of the subframe on the subframe retraining bolts will cause twisting of the differential on its mounting points.



                        If the subframe were more rigidly attached and held captive to the body, then there would be very little movement. A butt strut does this, but when a body brace is also used in conjunction, then the subframe retaining bolts must remain vertical and in a fixed position because they will be held capitve at both ends of the bolts. The diagram below shows how this works.



                        I think the boot floor issue is more likely to be of poor welding during manufacturing rather than a design fault. But having said that, the weak mounting points of both the differential and the rear ARB are design faults which will test any structural weakness present. I am definitely going to make my own bodybrace because I think this will prevent any tendency to diff mount failure and since it's a "bolt on" mod no welding to the structure of the car is required, although I can also do that myself.
                        /// Exdos ///
                        "Men who try the impossible and fail spectacularly are infinitely superior to those who reach for nothing and succeed" --Napoleon Bonapart

                        Comment


                        • #42
                          I don't think the diff is attached to the subframe at the front (I wouldn't have thought so as it wouldn't make sense being attached to a suspension component; it's not a live axle). I can't see movement of the subframe affecting the diff that much, if at all, since its not directly connected and the plunge on the driveshafts would remove any possible movement in the way you diagram suggests IMO.

                          I also don't think that the body brace would do much on the Coupe as the shell is pretty stiff anyway, and (assuming you're meaning bracing the pins on the subframe) it wouldn't prevent the designed movement of the subframe through the bushings. Obviously if you have stiff/solid subframe bushes then the pins are the next to flex but as said above I dont think this would directly affect the diff.

                          Comment


                          • #43
                            Originally posted by c_w
                            I don't think the diff is attached to the subframe at the front (I wouldn't have thought so as it wouldn't make sense being attached to a suspension component; it's not a live axle). I can't see movement of the subframe affecting the diff that much, if at all, since its not directly connected and the plunge on the driveshafts would remove any possible movement in the way you diagram suggests IMO.

                            I also don't think that the body brace would do much on the Coupe as the shell is pretty stiff anyway, and (assuming you're meaning bracing the pins on the subframe) it wouldn't prevent the designed movement of the subframe through the bushings. Obviously if you have stiff/solid subframe bushes then the pins are the next to flex but as said above I dont think this would directly affect the diff.
                            The diff is NOT attached to the subframe; it's attached by brackets to the bodyshell. I haven't suggested otherwise either in words or in my diagrams. What I am suggesting , and my diagrams seek to show this, is, that any movement of the subframe will cause slight fore and aft movement of the wheels (not necessarily always equally on both sides) which will act as levers on the diff, thus causing slight twisting of the differential on its mountings, thereby putting strain on the relatively weak mountings. Eventually. this may produce metal fatigue of the mounting points resulting in tears and ultimate failure.

                            Tying the two subframe bolts together with a Strongstrut butt strut will considerably reduce any tendency of the subframe to move on the bolts. Fitting a body-brace to the butt strut will take this a step further and will prevent all movement of the suspension bolts, thus keeping the subframe bolts absolutely rigid. The purpose of a body-brace on an MC would not be to stiffen the bodyshell (and I doubt if it can do this either on a Z3 roadster either), but instead, it is to do what I've described above.

                            I know that you also have a butt strut fitted, but if you don't think my explanations are accurately describing how the butt strut actually works, then can you please enlighten me as to how it does work?
                            /// Exdos ///
                            "Men who try the impossible and fail spectacularly are infinitely superior to those who reach for nothing and succeed" --Napoleon Bonapart

                            Comment


                            • #44
                              Originally posted by exdos
                              Originally posted by c_w
                              I don't think the diff is attached to the subframe at the front (I wouldn't have thought so as it wouldn't make sense being attached to a suspension component; it's not a live axle). I can't see movement of the subframe affecting the diff that much, if at all, since its not directly connected and the plunge on the driveshafts would remove any possible movement in the way you diagram suggests IMO.

                              I also don't think that the body brace would do much on the Coupe as the shell is pretty stiff anyway, and (assuming you're meaning bracing the pins on the subframe) it wouldn't prevent the designed movement of the subframe through the bushings. Obviously if you have stiff/solid subframe bushes then the pins are the next to flex but as said above I dont think this would directly affect the diff.
                              The diff is NOT attached to the subframe; it's attached by brackets to the bodyshell. I haven't suggested otherwise either in words or in my diagrams. What I am suggesting , and my diagrams seek to show this, is, that any movement of the subframe will cause slight fore and aft movement of the wheels (not necessarily always equally on both sides) which will act as levers on the diff, thus causing slight twisting of the differential on its mountings, thereby putting strain on the relatively weak mountings. Eventually. this may produce metal fatigue of the mounting points resulting in tears and ultimate failure.

                              Tying the two subframe bolts together with a Strongstrut butt strut will considerably reduce any tendency of the subframe to move on the bolts. Fitting a body-brace to the butt strut will take this a step further and will prevent all movement of the suspension bolts, thus keeping the subframe bolts absolutely rigid. The purpose of a body-brace on an MC would not be to stiffen the bodyshell (and I doubt if it can do this either on a Z3 roadster either), but instead, it is to do what I've described above.

                              I know that you also have a butt strut fitted, but if you don't think my explanations are accurately describing how the butt strut actually works, then can you please enlighten me as to how it does work?
                              I was speaking outloud re the diff being attached to the subframe rather than inferring you were saying it was. However, your diagram shows that the subframe movement would make the diff move but as I said driveshafts are designed to cope with all kinds of suspension angles wihtout affecting the diff so I can't see the subframe affecting it. The subframe, by design, is allowed to "float" on the 2 pins through the bushing, the trailing arms attached by further bushes also move but the diff is not affected by this movement (unless it was extreme movement beyond the designed movement limits of the suspension/driveshaft joint)

                              Any slight subframe movement you are suggesting that affects the diff pales into comparison against the amount of natural suspension/wheel travel that the driveshafts account for.

                              Comment


                              • #45
                                c_w,

                                I am aware that the prop shaft and drive shafts allow for play. But you've still not told me how the butt strut does it's work if you think my explanation is wrong?
                                /// Exdos ///
                                "Men who try the impossible and fail spectacularly are infinitely superior to those who reach for nothing and succeed" --Napoleon Bonapart

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