Subframe overhaul - input needed

[1FastSicilian]

Hi all,

I picked up a spare subframe to do a full rear end overhaul. The car really doesn't need it but being that it's all stock and original from 2013, it's a project I always talked about doing when I got this car.

I already ordered new OEM diff bushings, and plan on getting either CMP or BW solid subframe (thoughts on these two?)

Now, theres 4 other bushings that need to get done as well. Trailing arm and spring arm bushings.. I'm torn between the ones offered by BW or just going OE. There is a SIGNIFICANT price difference so I'm trying to find a way to mentally justify the BW bushings.

https://www.bimmerworld.com/BimmerWo...aring-Kit.html

One downside is these need a tack weld to hold the sleeve in place.

My car is not a dedicated track car, only sees 3-5 events a year and I do drive on the street.

What did you guys all do? or would you do in my situation..

PFA

[bipp]

I went with the CMP bushings and camber arm bushings (effectively same as BW). Not convinced it led to significant NVH worsening (although that could be due to doing too much at the same time) but I do believe it improved the feel of the car. The reasoning behind CMP's bushings make sense - especially if you think you'll run eccentrics or anything else for roll center correction down the line. There's another bushing that I believe Fall Line or ASSIST / Laptorr has - https://www.m3post.com/forums/showthread.php?t=2135761. CMP has a conversion shim kit iirc which I ordered but did not go ahead with due to concerns about shearing - if I had seen these when I was having my rear bushings done, I likely would have added these while I was there.

If you're doing it once - may as well go for the solid bushings. Especially if you aren't daily driving this car (I see that you replaced the Ram with an X7?).

[1FastSicilian]

Originally Posted by bipp

I went with the CMP bushings and camber arm bushings (effectively same as BW). Not convinced it led to significant NVH worsening (although that could be due to doing too much at the same time) but I do believe it improved the feel of the car. The reasoning behind CMP's bushings make sense - especially if you think you'll run eccentrics or anything else for roll center correction down the line. There's another bushing that I believe Fall Line or ASSIST / Laptorr has - https://www.m3post.com/forums/showthread.php?t=2135761. CMP has a conversion shim kit iirc which I ordered but did not go ahead with due to concerns about shearing - if I had seen these when I was having my rear bushings done, I likely would have added these while I was there.

If you're doing it once - may as well go for the solid bushings. Especially if you aren't daily driving this car (I see that you replaced the Ram with an X7?).

Thanks for your response. I don'tknow if I'll go crazy chasing all the roll center correction parts. but as I think about it, i might just go with OEM replacement for these bushings..

Yes I did! Wife didn't like driving the truck and I needed something she could drive as well.. got a nice X7 with every option on trade in so figured I'd grab it.. Plus it can tow 7k+ lbs!

[bipp]

Originally Posted by 1FastSicilian

Thanks for your response. I don'tknow if I'll go crazy chasing all the roll center correction parts. but as I think about it, i might just go with OEM replacement for these bushings..

Yes I did! Wife didn't like driving the truck and I needed something she could drive as well.. got a nice X7 with every option on trade in so figured I'd grab it.. Plus it can tow 7k+ lbs!

It might make sense for you to reach out to Cayn at CMP to get some sort of a consult - when I emailed, Cayn was heading out on paternity leave but gave pretty great detail into the benefits of the parts / roll center correction. Otherwise, OEM bushigns are always a safe option for a refresh unless you have someone who can go over the geometry with you.

Nice! A big comfy SUV that can tow the M3 with room to spare sounds like the perfect daily.

[Redd]

Don't worry too much about NVH on the rear subframe. You can pretty much go solid everything (except diff bushings) and not add any NVH. You'll just get a slightly firmer ride. I have solid everything and my car is a street car.

[bipp]

1FastSicilian I went and found my email thread with Cayn and sent it to you on Discord with the relevant message, pretty sure that's more useful than whatever I can ramble about in the context of a forum thread

[gh0stE92M3]

If you have the subframe out just get solid subframe bushings, don’t get oem diff bushings as you will need to service them again, I have delrin diff bushings, your car is pretty dialed in and I think it would benefit from the mk bushings in the rear to correct the rear geometry. It’s a little more costly but I think will be a better than going with oem. Do you have adjustable rear arms?

mk bushings

[bipp]

Originally Posted by gh0stE92M3

If you have the subframe out just get solid subframe bushings, don’t get oem diff bushings as you will need to service them again, I have delrin diff bushings, your car is pretty dialed in and I think it would benefit from the mk bushings in the rear to correct the rear geometry. It’s a little more costly but I think will be a better than going with oem. Do you have adjustable rear arms?

mk bushings

I saw this and wonder what the actual effect on geometry is. I know tlrid3r did something similar by making his own parts.

The CMP pieces (F and R) allow 8mm of roll center correction with stock arms.

[sperkins]

Originally Posted by 1FastSicilian

Hi all,

I picked up a spare subframe to do a full rear end overhaul. The car really doesn't need it but being that it's all stock and original from 2013, it's a project I always talked about doing when I got this car.

I already ordered new OEM diff bushings, and plan on getting either CMP or BW solid subframe (thoughts on these two?)

Now, theres 4 other bushings that need to get done as well. Trailing arm and spring arm bushings.. I'm torn between the ones offered by BW or just going OE. There is a SIGNIFICANT price difference so I'm trying to find a way to mentally justify the BW bushings.

https://www.bimmerworld.com/BimmerWo...aring-Kit.html

One downside is these need a tack weld to hold the sleeve in place.

My car is not a dedicated track car, only sees 3-5 events a year and I do drive on the street.

What did you guys all do? or would you do in my situation..

PFA

I would go solid, or spherical on everything, except the diff bushings. I went with 95D poly on the diff, and the noise is tremendous (the back half of my M is completely gutted). The only downside to the subframe/suspension conversion is the install. It’s a pretty physical process pressing everything in. No concern if you have a shop do it.

[danvitmon]

Rogue engineering has drop in spring arm bearings that don't require a tack weld. I bought them and they're a nice piece, but I haven't installed them yet.

https://www.rogueengineering.com/Rog...air_p_284.html

[gh0stE92M3]

Originally Posted by bipp

I saw this and wonder what the actual effect on geometry is. I know tlrid3r did something similar by making his own parts.

The CMP pieces (F and R) allow 8mm of roll center correction with stock arms.

quick explanation of correcting geometry

It’s one of those if you’re gonna do it, just do it once and forget about it.

I wish I would’ve just went this route front the get go. I have the full Spl catalogue and solid subframe bushings. I have solid delrin diff bushings, at the time I got the bimmerworld sperical inner spring arm bushings. The rear end is pretty solid the only bushings I have left that are rubber are the trailing arms. The only nvh I have is from my drexler diff and 4.10 fd lol

I’ve changed out everything else also bimmerworld group n motor mounts and rev shift 70a transmission mount and I don’t notice any vibrations like many people warned me would happen.

But like some have concluded just go full solid and spherical you built that car fora purpose. Once you do that it’ll be complete.

[tlrid3r]

I basically did the offset busking for lower spring camber arm and trailing arm as it also corrects equally to ensure no bumper steering on the rear.
MK is basically exactly the same:
https://shop.ammotorsport.ch/produkt...-ch-gutachten/

[amg6975]

Originally Posted by Redd

Don't worry too much about NVH on the rear subframe. You can pretty much go solid everything (except diff bushings) and not add any NVH. You'll just get a slightly firmer ride. I have solid everything and my car is a street car.

Second this. Solid everything you can, the difference is noticeable but NVH is largely unchanged.

[mikentosh]

I went browsing through the links mentioned in here, and came across this offset bearing from BW for the inner side of the spring arm:

https://www.bimmerworld.com/Suspensi...aring-Kit.html

Wondering if anybody has feedback on this? It would be for a dedicated track car.

[gh0stE92M3]

Originally Posted by mikentosh

I went browsing through the links mentioned in here, and came across this offset bearing from BW for the inner side of the spring arm:

https://www.bimmerworld.com/Suspension-Steering/Urethane-Bushings/BimmerWorld-F8X-G8X-Rear-Camber-Arm-Offset-Bearing-Kit.html

Wondering if anybody has feedback on this? It would be for a dedicated track car.

If it’s a dedicated track car just get the mk bushings to have full adjustability of the geometry correction. The BW is just one bushing.

[darren p.]

Originally Posted by gh0stE92M3

The rear end is pretty solid the only bushings I have left that are rubber are the trailing arms. The only nvh I have is from my drexler diff and 4.10 fd lol

Would you say this is more a function of the solid delrin diff mounts or the diff/final drive itself. I got the Powerflex street diff bushings but didn't think the drexler or the 4.10 would add NVH...if it does, so be it.

Originally Posted by gh0stE92M3

If it’s a dedicated track car just get the mk bushings to have full adjustability of the geometry correction. The BW is just one bushing.

And if its not a dedicated track car would you recommend the normal, non-offset BW bushing? How low do you have to be where roll center correction is an issue?

OP - I'm doing a similar refresh and there is no way I'm putting any rubber back in there. A tack weld should not be a reason to stop you from doing that inner bushing on the spring arm!

[gh0stE92M3]

Originally Posted by darren p.

And if its not a dedicated track car would you recommend the normal, non-offset BW bushing? How low do you have to be where roll center correction is an issue?

OP - I'm doing a similar refresh and there is no way I'm putting any rubber back in there. A tack weld should not be a reason to stop you from doing that inner bushing on the spring arm!

I think the combination of both the delrin bushings and the final drive mechanism is contributing to the sound. Under 3500 rpm it’s not as audible sounds like stock just a slight whine from the delrin bushings.

I think my case it’s a little more exaggerated because I don’t have my rear seats in and I don’t have the rear seat delete in place yet.

You can do the bw offset bushing and that should help, I don’t know how low you are. That bushing address one aspect of the rear geometry. When you lower the car it changes the the roll center. I’m no expert in this and I know there’s a science behind it all. But I know when I lowered my car and did the front Spl arms which fixed the front roll center and bump steer the fron grip was increased and so in theory the rear will match the amount of grip the front has and be more predictable.

I thought about switching to poly diff bushings but it really doesn’t bother me to much I just need to make my rear seat delete. I’m planning to insulate the delete and wrap it in acoustic carpet vs the Alcantara. I want to make it match the carpet and I’m already going to be doing a black dye for the rear trunk trim.

I’ll post some pictures once I have it all done. I don’t drive the car much but will be taking it out more once the weather warms back up.

[bipp]

Originally Posted by gh0stE92M3

quick explanation of correcting geometry

It’s one of those if you’re gonna do it, just do it once and forget about it.

I wish I would’ve just went this route front the get go. I have the full Spl catalogue and solid subframe bushings. I have solid delrin diff bushings, at the time I got the bimmerworld sperical inner spring arm bushings. The rear end is pretty solid the only bushings I have left that are rubber are the trailing arms. The only nvh I have is from my drexler diff and 4.10 fd lol

I’ve changed out everything else also bimmerworld group n motor mounts and rev shift 70a transmission mount and I don’t notice any vibrations like many people warned me would happen.

But like some have concluded just go full solid and spherical you built that car fora purpose. Once you do that it’ll be complete.

i do get the concept of roll center correction and its necessity as we lower the cars

however, with the roll center somewhat adjusted from the cmp subframe bushing, i'm wondering if it makes sense to further adjust it with the offset bearing, or if "over correction" is liable to occur

[gh0stE92M3]

Originally Posted by bipp

i do get the concept of roll center correction and its necessity as we lower the cars

however, with the roll center somewhat adjusted from the cmp subframe bushing, i'm wondering if it makes sense to further adjust it with the offset bearing, or if "over correction" is liable to occur

I think the idea of the offset bushing is to use that on its own. I don’t think using both in conjunction would be needed.
I think also using the bw bushing is one bushing addressing the roll center, but you also have to adjust for the bump steer as well. That’s where the other offset bushing come in to adjust the trailing arms and outer spring arm.