BMW Tech Corner - E46 M3 Rear Subframe Reinforcement
After years of aggressive driving, hard launches and hard 1-2 shifts, the under supported rear subframe mounting points in the E46 M3 can fail. Thin sheet metal and a lack of reinforcement leads to small hairline cracks, torn welds and in the worst case scenario, the entire trunk floor can separate, ultimately leading to an extremely costly repair and a very dangerous car to drive.
EuroMpire highly recommends adding the proper reinforcements before a repair is needed. Additional rear supports can be added to vehicles that may often experience higher stress conditions found in racing or high horsepower applications.
As always, the E46 M3 Rear Subframe Reinforcement process begins by disconnecting the vehicle battery. We then remove the rear subframe, fuel tank, and the entire interior trunk covering.
After stripping the paint from all known affected areas, we begin our initial inspection. We check for hairline cracks, pulled or separated spot welds (155 of them), torn or compromised sheet metal and general signs of stress or fatigue.
During the inspection process, if any failures are found, we must develop a plan to repair them. We must follow the cracked or damage material to the end, assess the damage and move forward.
If no failures are found we install the reinforcement plates. 16 gauge steel plates are welded around all 4 subframe mounting points. Precision holes are cut into the trunk floor to gain access to the top of the mounting points. These spots are reinforced, then the holes are covered.
Once the car is back together, we perform a 4 wheel alignment. The vehicle is then test driven to insure all repairs are solid and the vehicle “tracks” properly. After the road test, we double check all work and repairs and the BMW E46 M3 Rear Subframe Reinforcement repair is COMPLETED!!
We then paint all the repaired or reinforced parts with new undercoating. Allow the proper drying time and later begin the assembly process.
Note: While the rear subframe is out of the car this is a good time to optionally replace the rear subframe bushings, differential bushings and any other worn components.
We encourage all M3 owners and potential owners to have their cars inspected for failures or (hopefully) previous repairs.
Having the reinforcement procedure done before failures occur will save you thousands of dollars. The average cost of the reinforcement is $1500.00 The cost of the repair after a failure would be determined on a case by case basis.
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