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03-15-2017, 03:34 AM | #1 |
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Schmiedmann M3 Control Arms DIY Video
Got this in my mailbox this morning via Schmiedmann's newsletter. Thought some would enjoy the DIY video, especially since it's on the E82.
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03-15-2017, 09:51 AM | #2 |
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This is good but maybe not perfectly clear on the torqueing of the fasteners. Here is something I posted on the E90 forum on a related discussion:
Quote: Remember to: • Make sure thread bores, bolts, nuts and mating surfaces are clean. • Install bushing end of control arm to subframe using new fasteners. Do not tighten nut at this time. • Install control arm ball joint to steering knuckle using new selflocking nut. Tighten fully. • Install ride height sensor link rod to control arm (if applicable). • Install wheel and lower car. • Tighten bushing end of control arm to subframe with car on ground and loaded. Bounce suspension a few times before final tightening. Endquote The quote above is for the control arm but the tension strut instructions are essentially the same. Another point worth noting is check what grade of nuts and bolts you have. I had grade 10 nuts for the subframe nuts and bolts so torqued accordingly (from Bentley). Then I thought I'd take a second look at everything and had an 'aw shit' moment when I saw the bolts were grade 8. So I had overtorqued them. This worried me enough that I parked the car and ordered new nuts and bolts and changed them out. At $50+ screw up!! |
07-19-2019, 08:41 PM | #3 | |
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Quote:
I responded in a torque thread and would appreciate your perspective. https://www.1addicts.com/forums/show...4&postcount=16 I don't want to do it again if I don't have to!
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07-19-2019, 11:53 PM | #4 | |
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I believe my bolts were grade 10.9 but the nuts were 8.8. I went under a weakest link theory and changed them and torqued at the 8.8 spec. I found some general fastener grade & torque discussion that led me to that decision. I'm sure some will say that was overly cautious. Maybe even incorrect as the bolts are torque to yield and the idea it to get some amount of stretch?? I just felt that I had torqued bolts beyond the recommendation and that they would have been compromised. Are the bolts and nuts you used grade 10.9 or grade 8.8? If they are 10.9 you don't have a problem. If the bolt and/or nut are 8.8 you've got the same decision I had. In that case my obvious advice (obvious b/c that is what I did) is get new fasteners and torque to grade 8.8 spec. BTW, the BMW TIS site has the same torque specs depending on fastener grade. https://www.newtis.info/tisv2/a/en/e...mounts/5bUExgU
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07-20-2019, 12:13 AM | #5 | |
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Quote:
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07-20-2019, 07:25 AM | #6 |
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The torque spec is more based on what you are fastening over what bolt is used. You can have the exact same bolt/nut in three different places in the suspension, and they can have three different torque specs.
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07-20-2019, 08:49 AM | #7 |
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Yes but since Bentley and TIS give the 2 bolt grades with different torque instructions, I didn't want to use the higher grade spec. Also, anything I dug up showed a 8.8 grade bolt max torque ~100 Nm (depends on pitch and friction coefficient). Just wasn't comfortable to torque it to 100 Nm + 90 deg.
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07-20-2019, 12:39 PM | #8 | |
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However, What I discovered today is that the older manual states both 8.8 and 10.9 specs in the torque section but the newer one only lists one spec, the 10.9 spec, in the equivalent section without specifying it is 10.9. If I had just pulled out my *old* Bentley manual, I would have gotten it right! A little frustrated with Bentley right now. Glad I stumbled across your comment...wish I had stumbled across it two days earlier...
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07-20-2019, 01:10 PM | #9 | |
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However, I'd still be uneasy b/c of what I said about finding ~100 Nm as the max torque spec for m12 grade 8.8. Maybe someone with an engineering background will chime in here.
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07-20-2019, 02:05 PM | #10 | |
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That would be helpful...where's fe1rx ?
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07-20-2019, 03:47 PM | #11 |
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That would be great if he chimed in.
If you haven't already done so, search 'tightening torque for metric fasteners' and you will find nothing greater than 100 Nm recommended for a grade 8.8 M12 bolt. Based on this and the gut feel that the extra 90 deg is a lot, I went down my cautious path. Good news it isn't that much work to replace the nuts & bolts. Please post whatever you decide.
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07-20-2019, 05:09 PM | #12 | |
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The cost is really in time and frustration. Now I have to wait until next weekend to complete the job while waiting for parts. Glad this isn't my DD. All of this is 1st world problems, I know! To be clear, I decided to replace and retorque to the 8.8 spec.
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07-20-2019, 05:30 PM | #13 | |
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None the less, I think you're doing the right thing
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