11/5/2022 0 Comments E46 m3 subframe crack![]() Front reinforcing and clamping plates (all left in position for 1 week)ġ4. Reinforcing plates fitted and compressed into place with 2D clamping plates (rear), not something I have seen done but a must I reckonġ3. Plates coated with epoxy after scouring with 60 grit and cleaning with electrical contact cleanerġ2. RHF ok (circular shape around thread is not a crack, it is the boundary line between the body panel and the threaded insert)ġ1. #E46 M3 SUBFRAME CRACK CRACK#LHR mount ok apart from crack to the left (you need to look out for separated spot welds as well as cracks)ħ. Underside stripped and mounting points cleaned upĥ. Crack viewed through the RHR sway bar mount (exhaust removed)ģ. If anyone is interested I have the gear I used for this job available (diff/axle carrier frame, reinforcement plate templates, reinforcement plate clamps and foam dispenser gun).ġ. The reinforcement plate epoxy was $40/tube – I brought 4 but could have got away with 2. Regarding costs the BMW structural foam was $263 per pack (2 x 420ml tube pairs) – I brought 2 packs. ![]() A lot of people use a hand actuated epoxy applicator gun but this is very hard work, instead I made up a mechanised unit as per the following photos. This prompted me to use expanding foam to keep the structural epoxy localised around the mounting point, this is not something I have seen done before. Regarding the front mount, I spent a lot of time estimating the size of the cavity that the mounts are encased in and found that it is quite large. Regarding the rear mount, since I had the subframe out I chose to blank off the rear cavity (using expanding foam) from the bottom of the car rather than inside the boot as per BMW’s T.I.S. #E46 M3 SUBFRAME CRACK FULL#There are plenty of DIY’s out there so I haven’t gone into the full detail here, a few things to note though. The other 2 mounts (and ultimately the whole floor panel) really only seem to fail once these 2 stressed mounts have failed. ![]() The RHF subframe mount is subjected to compression stress (i.e. This is because the LHR subframe mount is subjected to tensile stress (from motor induced rotational torque (anti-clockwise look at the rear of the car) and axle induced rotational torque (anti-clockwise looking at the right hand rear wheel). I also decided to use the structural foam in the LHR and RHF cavities as these are the 2 places where the cracking normally begins. I had the necessary gear/skills to weld and it would have been cheaper but I felt it would have been too “invasive” when all things were taken into account. ![]() Based on this I decided to weld the crack, fit reinforcing plates, inject BMW structural “foam” and repaint the underneath of the car.īearing in mind that the size of the crack (small) + the internal and external reinforcing being applied I chose to epoxy the reinforcement plates on rather than weld them. After stripping the vehicle underside and inspecting all of the subframe mounting points I found that there was only 1 crack and that it was fairly small (30mm long). km’s) the instances increase exponentially. Why do our cars fail here? Don’t know but previously we could comfort ourselves that very few cars were affected but it seems to me that as time goes on (i.e. left hand rear subframe mount at the floor crease). In my case the crack was located in the classic spot (i.e. I found the crack after viewing a Reddish Motorsport video, I had looked before (with the entire subframe out) but I did not look in all of the right places so I don’t know if is new or was existing. I have been in 2 minds as to whether I should post my experience with the dreaded E46 M3 chassis crack, on one hand it is negative for resale purposes while on the other it is potentially good information for fellow Bimmersporters and I reckon the repair is up to any scrutiny. ![]()
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