E46 rear subframe carrier cracks

[DaveG]

I have a few m3's to do at the moment so I am will stick up some pics here and observations as I know a lot of people have concerns

This is the one I've just started. It a 02 manual car with 110k miles. Looks to be a well minded car

Subframe down


Cracks can be seen already






Bottom all cleaned down

Fronts




Rears

[DaveG]

Left arch crack


Spot welds popped




This is above the rear left mount in the boot


I then drilled down to the top of the 2 front mounts from under the rear seat. Most people don't appear to bother doing this but there is no point plating the car if you don't address these


Both front receivers on the front were cracked at the top

[DaveG]

Cut out over the rear mounts also


Drilled up through the receiver to access the threads




Cleaned things up and drilled the end of the cracks






Drilled out all the broken spot welds also. About 15 in total


Welded up






Stitch welded the arch

[DaveG]

Weld ground down. You have to resist the urge to grind it down nice and flat as you are thinning the metal out by doing that


This is under the top skin I cut away over the rear mounts
I drilled up through the mounts and the upper skin

You can see the hole highlighted here


In the top of the pic you can see the rear chassis leg.

It's hard to believe that bmw could be so stupid as to not tie these together
Instead the loads are transferred out to spot welds on the other panels. Also because it is so far from any fixed point it is going to flex a lot more.
It's very clear that welding on plates as per reddish etc will not help this situation. It will only kick it down the road till the whole panel pulls out of the car.

Here is a video of a boot floor on a car with 40k miles and bmw structural foam injected. It's amazing that they last as long as the do when you see this

https://www.youtube.com/watch?v=ee0VvI8SlEQ

I made up some plates to transfer the load to the chassis leg




Here is the top of the rear mount highlighted again. It a lot nearer to a structural point now.
This is not enough on its own as over time the flexing will fatigue around the bottom welds. It could be spread out by plating around here to spread out the load.
I'm going to use longer bolts up through the rear mount and then tie that into this area and the cage on this particular car

[DaveG]

I'm waiting on getting some custom bolts made and the reddish plates so moved on the the rod bearings







Bmw spec for oil clearence is .030-.070 so these are bang on in the middle.


Top shell in place


Cap shell in and arp bolts lubed up


Old shells


The car has 110 miles on it. I rand bmw and it had the rod bearing recall done at 35 k
So labour 75 k on them

This is probably the worst one. You can just see the copper showing


I wouldn't like to see a big lot more mileage on them

[Andy]

Epic work Dave, I was extremely impressed when I saw it in the flesh.

[schoonerm3]

Great work Dave.

[DaveG]

Made these up to go on top of the front and rear sockets.



Welded in place



Then tied it into the reinforcement plate
The longer subframe bolts will now go up through these with a nut on top which will tie the subframe directly to these.


Reddish plates








Primed and stonechip applied

[Bayerische]

Great work Dave.

[Chillipepper]

Is this a customers car or your own Dave?


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