[Cloud9...68]

Actually, the question is more generally related to the mounting of the strut, but in my case, it pertains directly to adding my D1R strut brace. My question is - what type of nuts should be used for the four M8 mounting studs (bolts in my case, with my Racers Edge camber plates) that hold the strut to the strut tower? Should I use lock nuts, ordinary nuts, or something different? I always felt a little uneasy about the entire weight of the front suspension, and all the forces associated with cornering and braking, being taken up by these four little bitty nuts (although it is common practice), holding the strut to that thin sheet metal that forms the strut tower (which on my daughter's 325i was badly bent, probably from taking a bump at high speed sometime in its life - at least the D1R strut tower brace bracket significantly strengthens the tower). Thanks.

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[tamathumper]

You mean to say you've replaced the original studs with bolts, and they did not come with matching nuts?

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[flash]

because he is using camber plates, other hardware is used



as for what to use in conjunction with the camber plates, the factory hardware is extremely soft (something like grade 2.) i would say you could probably use just about anything, but i'd go with grade 5. locknuts should be fine, and not a horrible idea.

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[Cloud9...68]

Tama,



Yes, since I'm using camper plates, I need to use bolts instead of studs. The bolts were supplied with the camber plates, but they're too short to accomodate the D1R strut brace brackets, so I'll have to buy some longer ones. And yes, for some reason, they didn't come with matching nuts, which I thought was strange.



Flash,



Thanks; I figured lock nuts might be a good idea. I'll buy the highest grade I can find.

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[flash]

just don't use stainless. it is more brittle, and will cause corrosion to the aluminum it touches.

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[MB968]

Since you are replacing the hardware, and because you are going to track the car, I'd buy 8.8 grade bolts and nuts, and I'd use a lock washer, plus a little removable loctite. Preferable, everything would be plated for a little corrosion protection.

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[flash]

ironically, as i tend to always use the best grade of anything, i'm not sure i'd go that high in this application. while better in radial, torsional, and deflection loading, i've found that in compression load the higher grade hardware can gall and be hard to remove. i think i'd stay with grade 5. it's still a significant upgrade from OEM.



as for the lock washer, they should work fine, and loctite would probably work, but since there is no heat in this location, a nylock would also work well and be simpler.

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[Cloud9...68]

Thanks for all the info. Who knew there's so much to this stuff. In fact, you can really "go nuts" here...





Terribly sorry....

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[flash]

ba dum bum

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[MB968]

[quote name='flash' timestamp='1360597648' post='138627']

ironically, as i tend to always use the best grade of anything, i'm not sure i'd go that high in this application. while better in radial, torsional, and deflection loading, i've found that in compression load the higher grade hardware can gall and be hard to remove. i think i'd stay with grade 5. it's still a significant upgrade from OEM.



as for the lock washer, they should work fine, and loctite would probably work, but since there is no heat in this location, a nylock would also work well and be simpler.

[/quote]



Can't agree with your first point at all, but I do always find you have an opinion. Been involved in 1000's of applications of higher grade bolts in the machinery world. A normal technique to reduce gauling is to use a higher hardness item, which for fasteners equates to a higher strength/grade. Equipment we built before WWII is still out there an being rebuilt every few decades. Used a lot of high strength bolts. Never seen a gauling issue with them. The only time I've seen gauling is with stainless hardware which tends to be lower hardness.



Suggest the lock washer for potential repeated removal as opposed to a locking nut, or a nylock. If it isn't going to be removed very often, I agree with the nylock.

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[flash]

i'm just telling you what i've found to be the case in suspension hardware under compression and extension loads. it doesn't make sense to me either. i stopped using grade 8 in that direction and i stopped having threads binding up. maybe it's the class of thread and the looser tolerances of grade 5.

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[MB968]

If memory serves, the tolerances are the same. There is only one set of go/no-go gauges used to qualify these. There shouldn't be any looser fit with a lower class bolt/nut. If there is, something isn't right.



I could see that the softer fasteners that you suggest may not get locked up as easily with debris as the debris could imbed itself easier. Might seem like gauling, but I think if you bisected one of these you'd find that it was actually actually a debris lockup/failure issue. One thing about the softer bolts, is they will twist off easier. Sometimes that makes for an easier removal.



To avoid this, virtually every bolt/nut I touch either gets loctite, or more often aluminum anti-seize. Either of these seems to deal well with the corrosion/debris issue that can end up with things twisting off. Guess I forgot to suggest that with Cloud, as to me its a given to use one of these two. It sure does make it a lot easier to take things apart the next time. And, that's true if the end of the bolt is a bit corroded from exposure. Wire brush it and back it out, the anti-seize will keep it from locking up. Even the loctite seems to offer some protection. If there is much debris damage, you may want to replace the fastener when you get it off. But at least it comes apart a lot easier.

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[flash]

i think the issue is that grade 5 is more ductile, and therefore suffers less damage to the material.

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[MB968]

Don't see how ductility plays into it. That's more an issue with cyclic loading, and fatigue failures, but not pickup or gauling. From your earlier comments maybe you assume that the "suspension hardware under compression and extension loads" also applies to the fasteners. The purpose of the torque that we put on a fastener joint it to avoid it going throught tension/compression loading. As long as the fastener is torqued properly, it only sees tension, never compression. We do that so we don't have to deal with cyclic loading and the reduced load level failures that can result. The suspension components do see cylclic loading, but not the actual fasteners. So, I'm not seeing your point.

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[flash]

wow - i haven't had this conversation in over 30 years, when i was first learning about fasteners in college engineering courses.



of course the fasteners see cyclic loading. whether they are torqued or not, each and every stroke of the strut adds force to the fasteners as it compresses and extends. the material of the fastener then absorbs or doesn't that force applied. torquing the fastener does not zero out that force, it only limits it. the grade of the fastener only gives a measured resistance to that force. remember that for every action there is an equal and opposite reaction. when a fastener is subjected to a force of extension, it reacts with compression when that force is released.



it is a well known issue with grade 8 hardware that in automotive applications they can appear "brittle". they aren't actually brittle, but sometimes act like they are. while they can resist failure at higher loads than grade 5, that which allows them to do that can work against you in some situations.



grade 8 definitely does not heat cycle as well as grade 5.



the bottom line though, is that the softer grade 5 seems to flex a bit more and not bugger up as easily in suspension applications like this. whether it is actually doing that, or it's a dirt issue, or what, i can't tell you. i can only tell you that every time i use grade 8 in this kind of situation, i regret it. when i use grade 5, i don't.



this would be entirely different if the load were static, and i would not hesitate to use grade 8, and do so frequently.

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[MB968]

Don't want to argue with your understanding of the loading, but it seems a bit rudamentary. Cyclic loading is normally referred to in engineeing as forces that cross zero, i.e. tension and compression. Bolts do not see that. The joint sees changes in force lever yes, but as long as it was properly torqued, the joint only sees tension in the bolt, and compression in the mating of the members. Its when you don't have this that the joint fails. If this is not your current understanding, you may want to go past the 300 classes and delve more into current graduate level understanding of how bolted joints work. There has been a lot of work since the 70's. I think some of the best work on acutal hardware testing of loaded joints was done by Thornley & Conley who did some pioneering work in the 60's/70's in the UK, Univ of Birm or Manchester, don't remember which. They tested hardware and showed how it worked or didn't and what it took to make a loaded joint act like a solid piece of metal. Since then, finite element modeling of bolted joints, or threaded fasteners have helped increase our understanding much more significantly.



I accept your anicdotal evidence, though it is inconsistent with mine. I just don't accept your understanding of why you are getting those results. You haven't shown me any science to convince me otherwise, so I think I will stick with using grade 8.8 suspension bolts. They are all over my Mazda suspension, and I suspect, though not sure, that they are all over our 968 suspension.



And, thanks for the banter. In retirement I don't get much chance to do this.

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[flash]

lol - 8.8 is roughly the same as grade 5, and thereby supporting my point



if i were talking about a sheer load, then i would choose grade 8. if i am talking about an extension/compression load, which undergoes cyclic vibration, like this mount, i choose grade 5. it may go against everything we learned in school, but it works. that's likely why the manufacturers do it too.



by the way, that's what we had to do in many of the DOD applications too. grade 8 stuff was coming apart and/or becoming unserviceable.

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[MB968]

Wow, you mean this was all about you misreading my original post where I suggested 8.8 grade, a metric grade. And then you suggested using a grade 5 which is actually an Imperial/english spec? And, as you should know roughly equivalent to the 8.8.



And, you have finally persevered long enough, now throwing in new non-appropriate terms for the bolts like cyclic vibration. I kept trying to get you down to the science/physics level to have a meaingful dialog. I'm out of here, as there is no sense in beating my head against a brick wall. I've given enough of the actual bolted joint science info here, that anyone who truly wants to understand the science can go get it themselves, as it is clear they'll likely only be mislead by this dialog.

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[rxter]

Well this partly explains why all the stuff I put together breaks...

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[flash]

no need to go off in a huff



lol - yes, when you said "grade" and "8.8" i read "8 grade" (or actually grade 8) and not "class 8.8"



it's "grade" for SAE and "class" for metric.



the terms i used are not inappropriate. it seems that you do not understand the situation at play, and are thinking about static load only, which is not what is going on in this application. this is a vibrational or shock load. the strut is constantly pushing and pulling on the hardware. if you understand suspensions, you can then apply the engineering basics of hardware to that.



in any event, we agree on the correct hardware, though i chose SAE and not metric. i still don't think in metric. i'm that old. when i first started designing for DOD, i still used a T-Square.

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