Before buying an E46 i’ve read a lot about it. Apart from being an heavy chassis, it had a major problem to address before anything else, mainly for a peace of mind while at the track.
The BMW E46 rear chassis, where it mates to the rear subframe, is prone to cracking. All the models were plagued by this problem and for sure the majority of the owners of an E46 with a mild cracked chassis doesn’t even know about it until it pops completely out. At the beginning I thought it was an internet myth to sell chassis reinforcement kit but after I joined some Facebook E46 owners group I understood that the problem is real.
So the only thing to do was to reinforce it. I bought from internet a set of 6 plates already cut to match the subframe mounting point and then I started removing the subframe.. my DIY subframe reinforcement work were just started.
This was after removing the subframe. As I expected there were no cracks. I believe they show only if the car was driven very hard or in the rainy/salty road countries that will more likely allow rust to form on the undercarriage.
To start welding the plates I felt like I had to remove the fuel tank. That’s not a complex job, everything can be done over jack stands. Just make sure you don’t have much fuel or the fuel tank will be heavy.
After everything was removed I started cleaning the surfaces from seam welder and dirt until bare metal popped out and i picked up my MIG gas welder. I suggest you to use only gas welders (no flux core) or better if you can go TIG. I have not many hours of welding by my side but I felt confident I could do the job.
Maybe cosmetically it’s not the best job you’ve ever seen but I am pretty confident it will hold just fine.
After welding all the 6 plates I painted with rust protection spray all the welded spots, 2 hands. Then hands more of black paint, then a polyuretane sealant (good product, it stays gummy and creates a perfect isolation from the environment) and then some black bituminous paint. The result was good. The welds were perfectly covered, no water can penetrate and there are no more empty spots anywhere! Should be good for 500+ HP.
After all the welding i decided to change my worn out bushing with some polyurethane bushings which are even easier than original to fit and add strenght to the rear end.
As you can see i still use stock struts with lowered springs and these will be removed in the future for a coilover kit.
I will update you if anything happens but I think it’s a solid setup.
If you have any question feel free to ask me, thanks for reading.