Subframe mount pulled away from RACP

[Nate047]

Hey guys, please help me prevent a very stupid problem from happening again lol.

I had to remove the cross member in front of the diff so I could access my front diff mount (CMP subframe mounts mean you can’t get at the bolt with everything in place) and as I was doing this, one of the front subframe mount nuts stuck on the stud and drove it out of the car, pulling one corner of the subframe away from the RACP. I noticed it and stopped after like half an inch.

Then I loosened all 4 subframe mounts and dropped the complete subframe and diff assembly about an inch from the body of the car so I could fit a Knipex in the gap, grab the hex washer on the stud, release the nut (heh) and then drive the stud back into place touching the RACP plate. Luckily nothing broke or stripped, but the subframe mount nuts are both warped into oval shapes and obv need to be replaced.

This whole thing was super super annoying and stupid. I want to make sure A, this does not happen again if I need to get into this area again, and B, why this happened? Did I mess something obvious up? Any thoughts or suggestions would be helpful. I’m pretty close to being able to drive the car again. I have to chip away at it an hour or two at a time maybe one day a week, so this whole shit has dragged on for fucking ages.

[bmwfnatic]

I’ll admit this happened to me as well, especially when using an impact.

In theory the stud needs to be torqued to 90 Nm, and the nut to 77 Nm (from memory) so under ideal conditions the stud is always tighter than the nut and shouldn’t come out… But that obviously doesn’t factor in anything but ideal conditions

[karter16]

but the subframe mount nuts are both warped into oval shapes and obv need to be replaced.

FYI those collar lock nuts are supposed to be oval, they are oval like that so that they clamp on to the thread and lock.


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[Nate047]

I’ll admit this happened to me as well, especially when using an impact.

In theory the stud needs to be torqued to 90 Nm, and the nut to 77 Nm (from memory) so under ideal conditions the stud is always tighter than the nut and shouldn’t come out… But that obviously doesn’t factor in anything but ideal conditions

When I was originally reinstalling the subframe some time ago, I believe I had either tightened down with a crows foot on my torque wrench, or if that hadn't worked, I would have just gone cro magnon and made sure they were on there as tight as possible which would have been higher torque than the nut at 77nm. I thought about threading this one out a little bit and trying to put some Loctite on there. Also interesting because it only happened on one side, and both were treated the same on the installation.

[Nate047]

FYI those collar lock nuts are supposed to be oval, they are oval like that so that they clamp on to the thread and lock.


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Good to know, so are those one time use or reusable?

[karter16]

Good to know, so are those one time use or reusable?

I'm not actually sure what BMW say, but I've reused mine without issue. I think so long as they stiffen up as you thread them on (e.g. they're still oval and not rounded out) then they'll be just fine.

[332]

Hey guys, please help me prevent a very stupid problem from happening again lol.

I had to remove the cross member in front of the diff so I could access my front diff mount (CMP subframe mounts mean you can’t get at the bolt with everything in place) and as I was doing this, one of the front subframe mount nuts stuck on the stud and drove it out of the car, pulling one corner of the subframe away from the RACP. I noticed it and stopped after like half an inch.

Then I loosened all 4 subframe mounts and dropped the complete subframe and diff assembly about an inch from the body of the car so I could fit a Knipex in the gap, grab the hex washer on the stud, release the nut (heh) and then drive the stud back into place touching the RACP plate. Luckily nothing broke or stripped, but the subframe mount nuts are both warped into oval shapes and obv need to be replaced.

This whole thing was super super annoying and stupid. I want to make sure A, this does not happen again if I need to get into this area again, and B, why this happened? Did I mess something obvious up? Any thoughts or suggestions would be helpful. I’m pretty close to being able to drive the car again. I have to chip away at it an hour or two at a time maybe one day a week, so this whole shit has dragged on for fucking ages.

pay someone who knows what they are doing, to work on your car. stretched oval nuts.. I can't tell you how many fasteners have turned to ovals in my life time. Weld the trunk and the hood shut asap

[Nate047]

Thanks for another helpful contribution