CMP Subframe Reinforcement Completed

[Dxj]

I’ve been looking to do the full subframe reinforcement for a little while as I track the car from time to time so I finally bit the bullet and got it done by Laszlo at Protodrive Autosport in central NJ. I know there are many solutions out there and even more discussion topics on which one is the best one. After doing good amount of reading on forums and different websites, I decided to go with CMP and do both the topside beam / front cups and bottom plates. It might be an overkill but I don’t want to have to do this again. Another consideration was if I get more into tracking and want to get a welded cage, this could be a good welded solution to connect to down the line.
Also, did bunch of “while you’re in there” items as well (CMP solid subframe bushings, OEM diff bushings, diff bolts, tack welding RACP pockets, front sway bar mount reinforcement, refinished subframe (POR-15), etc.
Interesting part, no noticeable cracks…for a 2001 manual with 90k miles (in case anyone was interested as I feel it’s a lottery with these cars). Here are some pics…I’ve been looking for them when I was thinking about doing this so wanted to share with the community.
Lastly, Laszlo was great so feel free to contact if you’re thinking about getting this done in NYC metro area.
protodriveautosport@gmail.com
iG: protodrive_autosport














Final look

[jet_dogg]

cool

[EricSMG]

Very cool. I feel like that’s the best kit available although I’ve been away for a few years. I also feel that the top beam is the real fix with the bottom plates really just backup, rather than the reverse. If I had a car with no obvious cracks I’d skip the plates and just go top beam and be done.

edit - except the right front mount gets smashed upwards during hard launches/shifts so there is a case for plates

[rbg]

I wonder when doing the top part of the kit only (have plates done already) how much you need to take apart (tank, subframe, parking brakes etc…)?

[jet_dogg]

Very cool. I’m feel like that’s the best kit available although I’ve been away for a few years. I also feel that the top beam is the real fix with the bottom plates really just backup, rather than the reverse. If I had a car with no obvious cracks I’d skip the plates and just go top beam and be done.

Despite the e46's structural shortcomings I'm still of the uncommon opinion here that the major contributor of this issue are worn out stock carrier bushings. You can reinforce the car until your blue in the face but the carrier will still hammer the panel with every torque input. Also there is no data on whatever the flavor of reinforcements the forum favors with worn out bushings. Now that would be truly interesting to me.

[Thoglan]

jet_dogg Eh, it's all guess work really because no one has tested it properly. But I would hazard to guess if you drove a car hard for a while the RACP would start to crack and separate regardless of how fresh the bushing is. Fundamentally the RACP is just not well mounted to the chassis rails. There was a rear brace in the M3 GTR strassenversion for this reason, but perhaps BMW didn't expect the oversight to become such a big issue on street cars.

Speaking from my own anecdotal experience, my car had some cracking so underside plates were put in and all new bushings done at the same time. In less than 2 years of normal driving (no track use/hard launches etc) there was already secondary failure at the wheel arch. This could be an issue with having plates and nothing topside to reinforce, but would at least suggest to me that the bushing are definitely not the primary contributor. I have since installed the complete CMP kit exactly as this thread outlines and it appears to be rock solid. If that doesn't hold the RACP in, nothing will...

[jbfrancis3]

Despite the e46's structural shortcomings I'm still of the uncommon opinion here that the major contributor of this issue are worn out stock carrier bushings. You can reinforce the car until your blue in the face but the carrier will still hammer the panel with every torque input. Also there is no data on whatever the flavor of reinforcements the forum favors with worn out bushings. Now that would be truly interesting to me.

Interesting theory. My immediate reaction is even worn bushings are capable of absorbing energy which severely diminishes any kind of impacting.

[heinzboehmer]

I wonder when doing the top part of the kit only (have plates done already) how much you need to take apart (tank, subframe, parking brakes etc…)?

Pretty much everything has to come out again. The two front subframe studs have a hex portion in the middle, so they can't come out unless the subframe is moved out of the way. And they need to come out as they get replaced with the longer studs that attach to the top bar.

You might be able to get away with just lowering the subframe, but the amount of extra effort to completely remove the subframe vs just lowering it is very little. Might as well remove it entirely and save yourself the struggle of trying to work around it.

[Tonggi]

would love more detail on that rear seat delete.

[terra]

Despite the e46's structural shortcomings I'm still of the uncommon opinion here that the major contributor of this issue are worn out stock carrier bushings. You can reinforce the car until your blue in the face but the carrier will still hammer the panel with every torque input. Also there is no data on whatever the flavor of reinforcements the forum favors with worn out bushings. Now that would be truly interesting to me.

Z4M uses the same bushings but does not see failures. E9x M3 bushing design is also similar and similarly does not see failures.

[jet_dogg]

jet_dogg Eh, it's all guess work really because no one has tested it properly. But I would hazard to guess if you drove a car hard for a while the RACP would start to crack and separate regardless of how fresh the bushing is. Fundamentally the RACP is just not well mounted to the chassis rails. There was a rear brace in the M3 GTR strassenversion for this reason, but perhaps BMW didn't expect the oversight to become such a big issue on street cars.

Speaking from my own anecdotal experience, my car had some cracking so underside plates were put in and all new bushings done at the same time. In less than 2 years of normal driving (no track use/hard launches etc) there was already secondary failure at the wheel arch. This could be an issue with having plates and nothing topside to reinforce, but would at least suggest to me that the bushing are definitely not the primary contributor. I have since installed the complete CMP kit exactly as this thread outlines and it appears to be rock solid. If that doesn't hold the RACP in, nothing will...

I should have clarified I meant lack of solid bushings. Most rubber bushings wear rapidly and bmw are notorious throughout the years for most rubber bushings failing prematurely (as compared to most cars) in e chassis cars. I don't think plates alone actually do anything but make things worse a little later on.

Interesting theory. My immediate reaction is even worn bushings are capable of absorbing energy which severely diminishes any kind of impacting.

I know there has been a little conjecture re: the topic of solid bushings and rear suspension dynamics but it's all theory and no data. With all that I've read and experienced in my years of e46 ownership, the problem is the carrier will hammer against the panel. Therefore it is my opinion that if the mounting points are solid or let's say fused via solid mounts, there will be no impacting against the carrier panel at those points and the shocks/springs will be forced to do their job. I don't know if the axle carrier is of the same design on other cars so I can't comment on those.

We need to see an undamaged carrier panel with solid mounts installed and no reinforcements over time to be inspected for damage at intervals. I may experiment with this myself. I also believe the diff mounts should be solid as well to match, again against forum dogma.

[Thoglan]

jet_dogg I am definitely not an expert, so perhaps someone with decent knowledge on the RACP stuff AussieE46M3 could give an opinion on that.

Intuitively though, I would assume a solid bushing would only reduce the dampening and increase the peak force acting on the already poorly attached boot floor. I would expect a solid bushing to accelerate damage in an RACP that has not been reinforced.

[jet_dogg]

Well I already read Aussie's long post on this topic before in another thread so he would only be repeating himself which would lead me to reiterating my point after his.

My point is if the carrier and panel are conjoined I imagine the forces would be less than a percussion style of incessant impacting against the panel. I don't know if anyone has any concrete data on what effect solid bushings installed prior to any damage have on the panel.

[Dxj]

would love more detail on that rear seat delete.

It’s just perforated hardboard wrapped in alcantara. Used cardboard to get the shape right first…it was a quick arts and crafts project to cover up the bottom portion of the rear seat. PM me if interested and I can send additional pictures.

[AussieE46M3]

Hey guys, Thought I'd check out the forum and saw I had a notification bringing me here. It's a Friday night and I've had a couple beers but I'll see what I can offer.

Z4M uses the same bushings but does not see failures. E9x M3 bushing design is also similar and similarly does not see failures.

From memory the Z4 chassis doesn't have a RACP and where it bolts to the chassis is two tube like extensions protruding downwards. I've never seen the underside of a Z4 in person and am reflecting on old images I saw what was probably years ago now.

What I do know for certain is that E9X M3's are hugely different to E46's. About double the size and installed from above not below. There's no protrusions from the bush and the core sits flush against the chassis with a locating pin rather than on a stud with a hex. I picked up an E92 M3 very recently and was literally working on updating my subframe bush design for the chassis today. Fun fact, it looks like I can raise it a few mm like I have with E30/36/46's.

Regarding the worn out bushing creating an impact against the chassis and harder material reducing dampening and increasing peak force under impulsive forces, in short, both are correct.

harder bushings obviously wont flex so just like stiffer shocks, are harsher on the chassis.

The worn bushing argument applies to just stock bushings and technically uses the same principle. The rubber becomes so weak and flexes so easily that it basically does nothing to slow down the momentum of the moving subframe resulting in the steel protrusion in the bush to ram/hammer into the underside of the chassis. This is worse than solid bushing as you have no dampening however, you're also giving the subframe a chance to build momentum before colliding while a solid bush braces thing rigidly.
The contacting surface are of the protrusions is also a lot less than the hex so you have an eve greater peak force on a smaller area thus creating a greater surface pressure.

I've seen some cars locally with Turner's old style of reinforcement installed which from memory is about 1.5mm that have deformed from worn rubber bushings hammering into the chassis. On this topic, I just spent my weekend fixing a car with only 116k km (aprox 70k miles) that had just Turner plates put in and need re-reinforcing and the subframe bushings were so worn that there were visible cracks in the rubber almost the whole way around the rubber core. It had also been hammering the chassis so hard the paint had come off the plate.

The theory the cracks and deterioration will only accelerate applies to both the chassis and the rubber bushings.

The reason the protrusion on the stock subframe bushings is an issue is that there's an air gap between the sheet metal you see underneath and the female threaded body inside the RACP. If this air gap was not present the surface would be laminated thicker resulting in a greater shear strength which would reduce flex and thus the rate of fatigue.
Even in that scenario I would change the bushings as the rubber would eventually wear and become a problem.