BMW aluminum sub frame repair

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This car needs a cradle for the same reason that the Corvette was totalled over a 1" crack: every authority in the auto industry forbids welding cast aluminum structural members.
 
Originally Posted By: Ethan1
This car needs a cradle for the same reason that the Corvette was totalled over a 1" crack: every authority in the auto industry forbids welding cast aluminum structural members.


Did you view the video I provided? If you did you will notice the factory welds the brackets to the sub frame, and they do a poor weld at that. It's there weld that fails.
 
Originally Posted By: HerrStig
Didn't the Fast and Loud guys weld up a GT 40?


Aaron tig welded it, and it appeared to be a very good job.
 
Originally Posted By: tig1
Originally Posted By: Ethan1
This car needs a cradle for the same reason that the Corvette was totalled over a 1" crack: every authority in the auto industry forbids welding cast aluminum structural members.


Did you view the video I provided? If you did you will notice the factory welds the brackets to the sub frame, and they do a poor weld at that. It's there weld that fails.


What video? I see a link to a forum with 2 pictures?
 
Originally Posted By: Rand
Originally Posted By: tig1
Originally Posted By: Ethan1
This car needs a cradle for the same reason that the Corvette was totalled over a 1" crack: every authority in the auto industry forbids welding cast aluminum structural members.


Did you view the video I provided? If you did you will notice the factory welds the brackets to the sub frame, and they do a poor weld at that. It's there weld that fails.


What video? I see a link to a forum with 2 pictures?


Video was a typo. Sorry. The two pics shows the brackets that broke from the sub-frame.
 
Originally Posted By: rooflessVW
Do you have photos of your repair?


No I don't. Even if I did, since Photo Bucket went south I can't seem to figure how to use a different system.
 
Originally Posted By: Ethan1
This car needs a cradle for the same reason that the Corvette was totalled over a 1" crack: every authority in the auto industry forbids welding cast aluminum structural members.


I wouldn't buy into that Corvette story too much, there is more to that story IMO than is being told.
The part tunnel cost almost 8K and even if the labor was 3x that its still not enough to total a 60K new car.
I cant see why the insurance company would pay 2x the money out when the don't have to.

I can see not welding a control arm or its mounting parts on the cradle but a sway bar bracket is not really a high stress part in comparison, the bar itself takes most of the stress if the form of torsion just look at the brackets and the small diameter bolts that hold them, they are very low strength parts.
 
Sure, don't weld cast aluminum. However, I'm fairly certain that the cross member is an extruded aluminum piece. The brackets that broke would be aluminum bar stock welded on. The Corvette chassis would have been stamped aluminum... Shouldn't have been to difficult to repair.

Only the outer mounts themselves should be cast aluminum here, and they're cheap enough to replace. Was this a car with active sway bars? Looks like it.
 
Originally Posted By: Trav
Originally Posted By: Ethan1
This car needs a cradle for the same reason that the Corvette was totalled over a 1" crack: every authority in the auto industry forbids welding cast aluminum structural members.


I wouldn't buy into that Corvette story too much, there is more to that story IMO than is being told.
The part tunnel cost almost 8K and even if the labor was 3x that its still not enough to total a 60K new car.
I cant see why the insurance company would pay 2x the money out when the don't have to.

I can see not welding a control arm or its mounting parts on the cradle but a sway bar bracket is not really a high stress part in comparison, the bar itself takes most of the stress if the form of torsion just look at the brackets and the small diameter bolts that hold them, they are very low strength parts.





Trav,
What breaks the swaybar bracket is a jolt to the suspension. My customers wife hit a large pot hole going about 45MPH. The other customer drove over a concrete wheel stop in a parking lot. There couldn't be much stress on the welded bracket because of how poorly the factory weld is. It's been 2-3 years since I welded these and I haven't heard back from them. However my weld was much stronger so I didn't expect to hear from them.
 
Originally Posted By: Trav
Originally Posted By: Ethan1
This car needs a cradle for the same reason that the Corvette was totalled over a 1" crack: every authority in the auto industry forbids welding cast aluminum structural members.


I wouldn't buy into that Corvette story too much, there is more to that story IMO than is being told.
The part tunnel cost almost 8K and even if the labor was 3x that its still not enough to total a 60K new car.
I cant see why the insurance company would pay 2x the money out when the don't have to.

I can see not welding a control arm or its mounting parts on the cradle but a sway bar bracket is not really a high stress part in comparison, the bar itself takes most of the stress if the form of torsion just look at the brackets and the small diameter bolts that hold them, they are very low strength parts.





The other repairs were $8k, plus it needed the trans tunnel which GM does not offer. GM stated that replacement would compromise the vehicle.
 
I've seen this happen to an E63 6-series with active roll. I don't know if it was a road hazard impact or the stress of the system that caused the right side sway attachment to fracture from the subframe, though it was relatively mild compared to the one pictured.

Dealer and indy shop both quoted thousands for replacement of the front subframe, even for a junkyard part in the case of the latter.

I directed them to a local welder/race car fabricator who repaired it for a fraction of the cost. I didn't hear of any issues with the repair before the car was traded in for another.
 
Last edited:
Originally Posted By: Carmudgeon
I've seen this happen to an E63 6-series with active roll. I don't know if it was a road hazard impact or the stress of the system that caused the right side sway attachment to fracture from the subframe, though it was relatively mild compared to the one pictured.

Dealer and indy shop both quoted thousands for replacement of the front subframe, even for a junkyard part in the case of the latter.

I directed them to a local welder/race car fabricator who repaired it for a fraction of the cost. I didn't hear of any issues with the repair before the car was traded in for another.


Both of my customers also told me the sub frame cost would be in the 5K+ range to replace. Paying that kind of money to get another sub frame with poorly welded brackets.
 
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