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      04-08-2021, 09:53 AM   #7
simon
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Drives: E92 Montego Blue 328i
Join Date: Mar 2005
Location: Atlanta, GA

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Quote:
Originally Posted by mattoak View Post
Thanks for the replies. I did some extensive searching and found the answers. The subframe to chassis bolts are 80 ft-lb and do not need to be replaced.

However the reinforcement strut to subframe bolts are 41 ft-lb + 90 degrees, so it sounds like these also need to be replaced.

After that I started going through the workshop manual, and it recommends replacing just about every nut in the front end. Things like the strut top hat bolts, strut pinch bolt and nut, sway bar bracket bolts, subframe reinforcement plate clip nuts. Not all of these (most don't) get tightened to a torque plus an angle. So I'm not sure how necessary replacing every single one is.

I parted it out and it would be an additional $150 in fasteners to replace them all. I have to return stuff to FCP anyway, so I think I'm going to buy all of it and then make a game time decision in the moment whether to replace or not. Things like the control arm and tension strut bolt/nut at subframe and nut at knuckle will definitely get replaced, as well as strut pinch bolt and nut. But the top hat bolts and the subframe reinforcement plate clip nuts I might just return.

Any opinions on all of these?
An angle specification on a torque value does not mean the fastener needs to be replaced. A torque to yield fastener needs to be replaced.

The reason you need torque + angle on a fastener is because of friction. The torque on a fastener comes from two sources: the clamping force & overcoming friction in threads.

At low torques the friction can be negligible. But depending on the materials, condition (dirt, lubrication, etc), the friction component can be significant and vary wildly. That's why you torque it to a certain torque setting, before friction becomes significant, then go to a certain angle. 90 degrees is always 90 degrees, regardless of whatever friction that must be overcome.

To conclude, an angle specification on a torque value does not mean the fastener is torque to yield. And for whatever it's worth, I've dropped my subframe twice and have not replaced any fasteners