BMW E46 Subframe Failure Fix for a 2000 328i with 84k miles

[MemphisRob]

Cautionary tale for anyone looking at an early(1999/2000) E46 (or to some degree any E46 or E36). I got what I thought was a sweet deal on a 2000 328i for $3k. Perfect daily I figured with 4 doors, 3 pedals and only 84k miles. I knew I should have done a PPI but the seller and I had some mutual friends and he had good maintenance records. Turns out it had complete “subframe” failure (it’s actually RACP failure.. which is the Rear Axle Carrier Panel).


There are aftermarket fixes..and I chose to do the CMP plates and topside chassis beam. All in with shipping from Australia the parts were about $680. The engineer that designed the system has been really helpful and is good with communicating via Facebook messenger.


If you pay a shop to do this repair it will likely be $3500-$4000 for just reinforcement plates (not the reinforcement beam) and I now understand why. You have to completely disassemble the underside rear of the car and then prep the subframe mount areas...and that is a holy pain in the ass. You will also look like a coal miner after removing the dirt, undercoating, and paint


But for real...the early E46 rear subframe bolts into brackets that are pretty much “superficially” plug welded in three spots. It’s ridiculous that BMW allowed these 3 little welds to be responsible to hold all the torque being put into the subframe by the diff.

So, I am almost done with the repair. I need to apply seam sealer and paint/undercoating. I have some pics and video taken along the way to help anyone else that has faced this issue. I was so impressed with the quality and fit of the CMP engineering reinforcement plates and chassis beam I wanted to share my experience. I asked Cayn at CMP if he would provide a forum discount and he will take 5% off if you mention you read about it here. I am not a shill. I have two E36M3’s and am buying another in a few weeks. I bought this E46 and had no idea the rabbit hole I’d go down because of BMW’s poor engineering. This subframe failure has been a colossal PITA, but I was very appreciate of the DIY fix CMP created.

https://youtu.be/6l13uFKOWz0

[MemphisRob]

So, a few additional thoughts on this.

1.) the CMP plates are larger than many of the plates available so that requires the gas tank to be removed
2.) you can get the gas tank out with the exhaust in place (as I did) but getting it back requires luck or a miracle so go ahead and remove the exhaust
3.) if you have some cracks forming already, the subframe bracket welds have likely already failed and plates address only part of the problem (it is likely no longer welded to the RACP)
4.) any fix will be a significant endeavor in time and/or cost, I figured that doing just plates was only half the solution so I chose to also do the chassis beam
5.) I experienced this issue on what appeared to be a well cared for relatively low
mileage car. If you consider buying an E46, make sure to get a PPI before you write a check.

Just to clarify, I paid full price for the CMP plates and chassis beam. My career is in sales (albeit Dental Supplies).. so I appreciate the value of referrals when warranted. The CMP is such a well engineered option I wanted to make sure others in the same predicament I was in were aware of it.

[MemphisRob]

Well, the job is done. It took a little time to trim the trunk interior carpet and panels but it was worth it. No more subframe worries for me!! One more tip, the upper and lower control arms are extremely difficult to align so
that you can slide the bolt through both sides. I borrowed some tapered punches to run as a guide that made the impossible possible.

https://youtu.be/u-y5udhdV1E