- June 6, 2022
- Posted by: Oceanside Motorsports
- Categories: Auto Repair, BMW Service
While the BMW E46 is one of the best models that BMW ever produced, these cars have a known common issue with the body of the car cracking where the rear subframe meets the rear axle carrier panel. This problem has been known to happen to BMW E46 325i, 328i, 330i, 330ci, and M3 models
E46 Subframe Problem
The subframe is attached to what’s known as the rear axle carrier panel at four main points. The rear subframe holds the rear differential and trailing arms all together. Over the years, you will begin to get cracks in the area where the subframe is connected to the body of the car.
BMW E46 rear subframes begin to fail for a few reasons. Because of the way that the torque is delivered from the gas pedal, to the rear differential, and then to the wheels, the mounting areas, and the bushings within them will eventually begin to wear. Bushing failure can be very common. It will all start with play in the differential, a 100lb diff on blown mounts will begin to rattle around, from there, every time you hit the gas the disc will begin to clunk over time because all that pressure is going straight through the chassis. Eventually – this can lead to the subframe cracking problem that we all fear.
SMG models are guilty of taking on this damage because they have been known to be harsh while shifting. With a manual car, you have the chance to feather the clutch more and create a smoother shift. The Rear Axle Carrier panels have been known to crack on all BMW E46 models – you could have a race car with 800K miles, or a perfect car with 80K miles, it still can happen to all of them.
How to tell if I have a cracked BMW E46 Subframe?
The rear BMW E46 subframe connects to the rear carrier at 4 main mounting points, surrounding where that subframe mounts to the rear axle carrier panel. With a flashlight, you can inspect each of these mounting points to see if there are any cracks coming from the surrounding areas.
To get a super accurate and confident idea of the condition of your subframe and rear carrier panel, the subframe should be lowered 1-2 inches so that we can fully inspect the mounting areas and see what is really going on underneath the subframe.
Any Other Areas of Concern?
From there, the next thing that can fail is the corner pocket where the rear trailing arm meets the chassis; it is far less common, but it can still happen. Another area that we have seen subframe failure is in the corner where the factory stitch welds meet. The factory welded seam can eventually begin to separate – it will just look like it is dirty, but really, there can be underlying cracks. To get a better view of this area, you can remove the rear driver wheel.
How To Fix a Cracked BMW E46 Subframe?
It’s good to check your subframe for damages as much as possible. The only legit way to fix a cracked BMW E46 subframe is with metal work. The best route to go is to weld in reinforcement plates in the areas where the rear subframe meets the rear axle carrier. If it is cracked, cracking, or not reinforced yet, reinforce it! The E46 M3 in the video example has a reinforcement plate that is stitch welded all the way around the mounting point.
There was a recall from BMW a long time ago that served as a band-aid, but ended up causing more damage than good. For the rear subframe recall, the E46 subframe area was cut into from the top of the where they would inject foam that would expand and fill the area and negative spots. This was not a good long-term fix and the cars that received the foam treatment, over time, continued to fail. At this point, the situation was now worse because you could not just get in there and weld to the flammable foam. These cars needed to be cleaned to an extra degree before doing any reinforcing.
Foam technique = no go. Metal work is the only way to correctly fix a cracked BMW E46 subframe. To properly weld the subframe, the subframe needs to be lowered from the car, repaired, and then the subframe will be ready for reinstallation.
In this example, these reinforcement plates have been stitch welded in to prevent further damage.
Cost of BMW E46 subframe repair:
While it can be unfortunate news to hear or see that the subframe on your BMW E46 is cracking, it is nothing that can’t be fixed! There are a lot of solid shops that have been doing these repairs for a long time and have it down to a process. There are also a few different things that can be done to further strengthen this area of your car and it can be a great time to perform some much-needed maintenance to the surrounding areas.
For a subframe repair at a reputable shop, one could typically expect this repair to cost right around $2000. If you have a cracked subframe, you can ask a shop about their process of doing these repairs to see how thorough of a repair they are performing. Another thing to keep in mind is, however far you are willing to go and how much that you are willing to spend during the process of a subframe repair, this is a great time to replace differential bushings, subframe bushings, and trailing arm bushings.
Keep your bushings healthy, inspect the subframe, if it’s not welded, weld it! Or just drive your car very gingerly. We perform subframe repair for all BMW E46 models such as BMW 325i, 328i, 330i, and even the BMW E46 M3. If you are unsure whether your E46 subframe is damaged and should be repaired, contact us today for a free vehicle health inspection! We are a BMW repair shop in Oceanside, CA, 92058, give us a call at 760-721-5500