RACP Failure After Plates

[mrgizmo04]

I thought you had to drop the subframe to get the new subframe bolts in?

The new bolts are longer so they can reach to the top cups. There is a guide included that threads into place where existing bolts are (remove existing bolt, thread the guide in) to help guide the long drill, but that does not require dropping the subframe. You do need to get under the car since that work is done from the bottom.

[DiscoWagon]

Which shop did the recent welding repairs?

[Dash1]

Have you talked to Cayn from CMP? He is very knowledgeable and accessible and easy to catch in a chat on FB. He might be interested to chat about your case. He also has interesting materials published https://cmpautoengineering.com/pages/technical

I’ll have to contact him. Thanks for the heads up!

[Sergmann]

thats a lot of cracks and after a 190k, the metal is pretty much fatigued. you may squeeze a little more life out of that RACP but im sure the cracks will come back. with that kinda, damage, its best to go with a whole new panel IMO

Agreed. The fix you have implemented will hold for a while but will eventually begin to crack again. The welds look good but there is a lot going on in the RACP that cannot be seen from the two accessible surfaces (top and bottom). The metal has fatigued and will crack again. Adding a top bar will help immensely and should be done ASAP. Given the mileage on the car it may not be worth the effort to replace the RACP but keep an eye our for more cracks in the future. The RACP I took out of my car for reference which showed virtually identical signs of cracking both top and bottom. There wasn't much holding it together, especially in the sprig pocket area.

[liam821]

Doing the plates is a no-brainer, especially if you already have damage down there like I did, but I think you should do the foam injection at the same time.

[heinzboehmer]

If you have plates already, you can do CMP kit from the top, you don't have to drop the subframe again.

I thought you had to drop the subframe to get the new subframe bolts in?

[mrgizmo04]

You should have installed a vince or Cmp Kit when you had everything out and stitch welded. Just double the work now because you have to drop the subframe to do that stuff anyway as far as I know.

If you have plates already, you can do CMP kit from the top, you don't have to drop the subframe again.

[r4dr]

You can reinforce parts all you want from the factory, someone will eventually break something. That being said, BMW really could have done more for the RACP issues.

[Speed Monkey]

Oh man OP/Dash, that blows. At least you got a good 100k miles out of it since the first round of chassis repairs. Stating the obvious here, the problem lies with the fact that our M car is derived from this...


...a 318i, which everyone can see is far and away from being a sporting car chassis. That 318i indicates it is just a chassis for a common passenger car, albeit one that is priced in the junior luxury car class of vehicles. Hell, even when BMW cooks-up a premium priced ($100,000 dollars+) and dedicated sports car in the form of the Z8, they still choke and can’t get it right; the Z8 suffers from the front shock tower support failing, and it’s symptom is a tweaked shut line between the hood and fenders.


Then again, even a Porsche, a true sports car maker isn’t immune from screwing the pooch. At least we don’t experience this... 🤔 🤬

[BMWahba]

You should have installed a vince or Cmp Kit when you had everything out and stitch welded. Just double the work now because you have to drop the subframe to do that stuff anyway as far as I know.

[mrgizmo04]

I wouldn't say a whole new panel. But definitely Vincebar/CMP type reinforcement is needed as it relieves the carrier panel from most of the stress from the subframe. I'd say its important to weld any existing cracks before installing one of the said components as well.

Have you talked to Cayn from CMP? He is very knowledgeable and accessible and easy to catch in a chat on FB. He might be interested to chat about your case. He also has interesting materials published https://cmpautoengineering.com/pages/technical

[mrgizmo04]

Did you read my post?

Literally the first sentence...

I think we need forum guideline to not post a response unless op's post is read in full and all the other posts that are part of the discussion also. Sometimes people read the title, think they know the question and come in guns blazing with a response. Unless you are just having fun and post nonsense (like I do sometimes).

[Dash1]

If you have damage that can be seen from inside the trunk then there will be a lot more damage underneath. You need to remove the subframe to find all cracks, since most of the time there will be some around the subframe mounting points and these will be covered up by the bushings.

+1

[heinzboehmer]

is it possible to inspect for crack just from the trunk? or do you have to remove the whole rear subframe to get a better look?

90k and driven the way it should have sounds pretty impressive for just plates.

If you have damage that can be seen from inside the trunk then there will be a lot more damage underneath. You need to remove the subframe to find all cracks, since most of the time there will be some around the subframe mounting points and these will be covered up by the bushings.

[trudriv3r]

is it possible to inspect for crack just from the trunk? or do you have to remove the whole rear subframe to get a better look?

90k and driven the way it should have sounds pretty impressive for just plates.