The E46 M3, being one of the best M3s made in the opinion of the BMW purists, started production in September 2000. Powered by the S54 engine producing 338 BHP this raspy straight-six will be known for revving to 8,000 rpm and giving a unique six-cylinder tone. Being front engine and rear-wheel drive much rotational force is transmitted through the rear subframe and onto the subframe mounts on the boot floor. Over time hairline cracks can develop on the floor pan caused by the stress that is exerted on them under heavy acceleration or aggressive driving.

To fix or prevent this from happening, we offer a solution. The Redish Motorsport E46 Rear Subframe Reinforcement Kit strengthens the area by using specifically engineered plates that are welded to the boot floor. The kit consists of 8 individual plates that have been developed to precisely fit the E46 M3 and all the known locations where cracks can occur. To get access to the areas, this involves stripping the rear of the car, removing the rear subframe and drivetrain. Following this we assessed the area for cracks (in this car quite a few), please see picture below.

We then MIG welded all the plates to the rear boot floor, giving the area a lot more strength and therefore permanently fixing the issue. While the car is in this state, it was the perfect time to address any corrosion underneath the vehicle, in this case, it wasn’t too bad, but we made sure it was all fully prepped and ready for underseal. We did this by stripping it back to bare metal, using a wire wheel and treating affected areas with Corrostop. Once it was to our high standard, it was prepped further to allow it to be undersealed. To properly underseal a car, we go through several stages to ensure longevity and proper coverage of all the affected areas. We do this by using etch primer; this provides maximum adhesion to the underside then high build primer. This is the thicker coat of primer that we then sand back to ensure there aren’t any imperfections and that it is smooth enough. Following this, our seam sealer is applied, ensuring that any joining panels are sealed in and ready for the next stage. Following this, the topcoat and clear coat are applied, sealing in this factory finish. Finally, we apply our cavity wax; this repels water, ensuring moisture won’t get trapped and will ensure the underseal looks fresh for years to come.

Before reassembling the rear subframe, we decided to tidy up the rear subframe components themselves with our in-house shot blasting machine. This strips back any surface corrosion and dirt, leaving behind a factory fresh component before and after photos below. Also, while the subframe is off the car, it makes it a lot easier to change and replace the bushes with upgraded Polyurethane bushes. Polyurethane bushes are more robust and far better suited to handle the twisting of being a suspension bush. This material is more resistant to heat, oils and UV rays. Polyurethane is also weatherproof and wear-resistant. We also restored the brake lines and changed the differential bushes, ensuring that these components won’t need replacing in the near future.

Following the reassembly, we checked the geometry and alignment was as it should be using our laser wheel aligner, before taking it on our pre-handover road test. From these finished photos below we can see the underside of this E46 M3 has now been repaired and protected, meaning this customer won’t have to worry about this issue again. Also, with the addition of underseal, it will stop the chances of any corrosion occurring underneath the rear, giving the customer no worries about driving it in the rain.

Vincebar and Gussets

If you have a BMW E46 M3, please get in contact for pricing or any other services we offer. Due to the age of these cars, some are starting to develop cracks, similar to the ones we just repaired, on the inside of the cabin. This would require a full internal strip and assessment to ensure there aren’t any significant cracks. We can find these issues by removing the rear bench, carpet and plastic trim to then reveal the rear seat panel and floor. If we did find any cracks, a similar process would need to happen with plates MIG welded over the affected areas with the addition of a Vincebar and Gussets also being fitted. It is slightly rarer to find these issues, but as the age of the E46 increases and more mileage, they will cover the likelihood of cracks developing increases.