on the 2013, they call it the 'Structural reinforcement panel' and it's part number 31106786568

The bolt is: 33306772888

The stiffening plate on the 2013 model does not also share the bolts with the sway bar which is good, it uses the same diameter bolts just shorter, so i have a strong suspicion that BMW will have spec'd the same rules for install but maybe with different values since it's a shorter bolt (35 v 55 mm).

I haven't found the directive yet but in the link above it should show.

I missed this earlier; that's the NUT they are describing here. So as I surmised, they should also be 'single use' as they are crushed locking nuts def. not meant to be re-used.

This will only be the case if the bolt was never fully tightened. The bolts i've taken out and measured are ALL longer than they started and grew each time I tightened. (it will not look longer it's only 0.08mm longer per cycle or so). The picture i took above shows clearly that the bolt is 36.25mm long in the thread count that should be 36.00.

Tightening to spec 4 times plus an unknown times it was done on the vehicle took the bolt to internal failure and one more time broke it in half.

It will not distort below maybe 70-80 N·m which will net you about 2/3 of the design clamping force. Clearly that is enough to not cause cars to suddenly start flipping over, but it also is a lot less than design.

When i reused my bolts i looked up the advised torque for M10 class 10.9 and would have set them to something close to that (67 N·m spec).

Torque'd to normal spec should be ok in my humble opinion, but until somebody actually does the research to determine for sure nobody knows. if the plate moves a tiny bit under certain suspension dynamics that will affect performance to some extent. Is it something anybody will ever notice, that's clearly up for debate.

I like the idea of maintaining the design clamp force but not have to replace the bolts so i'm upgrading to 12.9 bolts to achieve that.

measure the torque it takes to remove your 'seat of pants' tightening, i would be curious; when i removed my wife's they ranged from 68 down to about 20 ft·lb, which I would regard as not nearly ok. (one was 45, also not ok).

The *proper* method to re-use if you can't TTY would be to use a torque wrench and use lubricated torque values for M10; you'll have a decent clamp force and won't damage the bolt, it will be on the order of 7000 vs 9000# clamping force, which clearly has been working 'ok' for 'most everybody'.

(the reason for using lubricated torque, other than the bolt will likely be auto-lubricated on a 17 yr old car, is that without lubrication the torque to clamp force changes each re-use, so you either have to add torque or you'll lose clamp force).

My personal estimation is that the 9000# spec is more than needed and that if everybody just torqued the re-used bolts to normal spec or close, maybe a little higher, but not close to yield.

In my testing, I didn't get to yield until about 105 N·m so it would probably be pretty safe to use a dry torque of 80 N·m or such (again, i plan to experimentally derive some useful numbers).

Here's the idea: until you get to yield there will be a little bit of internal deformation but not much; if you pull to say half the way to yield strength, (10% over normal torque), especially if you start with a new bolt, coincidentally the math just worked out to 54 N·m to achieve that level of tension. (almost identical to the 56 N·m from design spec).

I'm very curious about the 56+45° solution it's a great hypotheses and definitely deserves testing. I'm sold on the just use bigger bolts properly torqued though it's too nice of a coincidence to get the same clamping force as design with normal torque, i call it kismet.

did you see the picture of the lug bolt that was over-tightened? I've recently removed over-torqued lug nuts and bolts that were more than double the spec.

Fortunately there is a decent amount of overhead that a normal person using a lug wrench is not likely to over-torque them but could by stepping on it pretty easily, but with impact it's quite easy.

Advised torque for M14-1.5 10.9 bolt is 202 N·m and BMW spec's 130 on at least my x5, not sure if different on the M sport or E70s.

Each bolt can handle 16,200# force, but that's at full torque, it's 'only' 14,169# per lug bolt at 130 N·m. that is 70,845# per wheel when properly tightened.

yield is 20% over proof so you will damage a lug bolt at about 180 ft·lb, (242 N·m)

On MY car, when i put the bolts back in, i think i used 4 of the original bolts and 2 new SAE 3/8 i had laying around. I can't remember how much i torqued them but will measure when i remove them to get an estimate. I did NOT TTY/TTA as I was unaware of the procedure when I did it, My 'M.O.' however is to look up the torque spec on my reference app and use that value, so that's almost surely what i did.

There is a problem with the 56 N·m plus 45°, which is that at enough applications it will still damage the bolt to the point it can break apart (from a big bump in the road for example); it's not 'mission critical' even if the one of the bolts holding the sway bar breaks (which would likely cascade to the other), you'll know immediately if it happens when you get the 110dB morse code of the sway bar slamming into the subframe. (experimentally confirmed).

What i noticed during my re-tighten to destruction experiment was that the yield not only was met at a lower N·m torque, it ALSO too less degrees of turn, and on the 5th and final tighten it was already at yield by about 45°, now the previous were all 90°, so it would take more times at 45 and if the 45 only gets you from 7500# to 8000# what's the point might as well just stay at proof load and advised torque of 49 ft·lb.

For holding the sway bar the bmw spec torque is actually less strong, since the bolt is pre-stressed to 9000#, it needs less of an impact to hit the tensile strength and break, and if you torqued them normally, it would be a stronger joint.

The TTY is all about the diagonal strengthening of the subframe.

Here's the thing: the front subframe has ZIP for rigidity as a parallelogram as made pretty obvious if you look at the drawing ;

http://www.realoem.com/bmw/images/diag_2qnn.png

The subframe is like the letter "U" it's open on the rear side and has nothing to keep it from twisting as a parallelogram other than the stiffening plate.

Here is where it comes into play: hit the brakes hard and have the right tires hit a patch of ice with the left tires on dry pavement; with a reasonable braking force of 0.5G now you have about 3000# force pushing backwards on the LEFT side of the car only. This is the condition for which this plate is designed. There are TWO circles about 1 sq in. on the back and one in the front that will get yanked with that force. It would also work to keep the back of the "U" from pulling apart but i'm not sure what forces would get applied there.

I finally remembered exactly what it felt like when i drove my X5 without the subframe stiffener; i likened it to a minivan wobble above but a couple days ago i remembered exactly what it felt like:

When i removed my stiffening plate, it was *exactly* like when i took the top down on my Z28 Camaro! every time i hit a bump i could feel a little extra jiggle like a harmonic; think tuning fork; perfect analogy considering the sub-frame is a big "U" like a tuning fork.

Others may not feel it, but just like I felt the difference every time i drove top-down with the Z, it was immediately obvious to me when i drove the X without the plate. (and oops when i forgot to put the rear bolts in, that was a very loud few miles, it sounded like i was driving a jackhammer).

So, at least a LOT of the mystery is resolved. I don't have the exact specifics but i've found out most of the 'why' and that's what was driving me nuts. I have a plan that suits me and have put out plenty of info that will let others find their comfort zone with respect to how they abuse their bolts. (not meant as an insult, the bolts are abused by design).

-awr

This is a very interesting point and also greatly added to the mass-confusion on the stiffening plate bolts; many of the bolts that are NOT overly stressed are also recommended for replacement, in what seems to be a clear-cut case of CYA; there is no logical reason to replace a 16mm bolt that isn't stressed to deformation.

I had been fairly certain that the bolts weren't stretched until i actually measured a couple of them. When i did the first test of re-tighten to spec and actually measured it grow by 0.08mm then after 4 more it snapped.

FYI; the advised torque for M10-1.5 10.9 is 49 ft·lb = 67 N·m and I am willing to bet that the 56+45° will not cause a loss of strength for well into the double-digits because there is a 20% margin in the design of bolts and that may be right in the middle.

For those like me with a digital torque adapter with live torque reading, it's darn simple to determine when the bolt goes plastic; the torque number just stops climbing it's bizarre! Like i mentioned right after my experiment, I noticed Also since i did one after the other after the other, that each successive time, the angle where the plastic deformation kicked in was sooner at each time, i will pick up one of the TTA tools for my detailed experiment i was only using 'start vertical, end horizontal' with the breaker bar for the initial test.

If you use a torque adapter, and follow the TTA specs, As long as the torque gets to 100 N·m before 90° There is still going to be life in that bolt. One of the bolts I put back in was over 115. I'm going to do a handful of new bolts to get a better scatter plot of what numbers to use, but with the right knowledge you can definitely use the bolts a few times at least.

Too bad the OEM bolts aren't $3.53 like real-oem says. The thing is, even if they were $3.53 + 78¢ (nut) that's still over $25 that need not be spent just to check on the oil leaking status.

I just thought of another biggie; in the example of braking while on ice, it only generated a sheer force of 3000#, in that example but it would be more than that because the lever ends are the tires, the bolts are in the middle there will be leverage factor so it could be double that in moderate braking and quadruple if you get near a 1.0g panic stop.

HOWEVER; bump into something on ONE side of the bumper and now you could easily get into the 10g range; if you put a 10g deceleration on one side of the bumper, now you are putting 50,000# force twisting the car into a parallelogram!

NOW it's coming together to make sense. When i did my early math to determine that the sheet was thick enough to hold back 50,000# of force it felt pretty serious and 'why that much' but it will GREATLY reduce the risk of totaling your car from a fender-bender.

Now i wish i had a couple end-of-life X5 to bump into something solid at 10 mph. The reason people aren't having problems with not tightening their bolts properly is they are good drivers :-D

Get into a fender-bender with your plate removed, there is a better chance you will total your car.

So, it's becoming clear that a large part of the point is to keep the car from twisting into a pretzel from an offset impact, the shear strength of an M10-1.5 is just about 8000#; but hardened aluminum has a tensile strength on the order of 40-50 ksi, so by using a strong 'pinch' they can get 10s of 1000s of # of resistance. just 'snug' that bolt and especially in the case like my wife's where one corner was 20 ft·lb, it doesn't drop to 8000# force, it drops to the sectional size of the cross of the bolt and the aluminum. That works out to 1/16 of a sq. in. so approximately 45/16 = about 4000# force to pull the bolt sideways through the aluminum.

I have to measure the clamping point on the car, but it was maybe 1.75", so that is about .27 sq. in. multiply by 45k and get 12,400#.

These are obviously a lot of educated guesses but they have sound backing in science. basically the idea is that with 9000# of clamp force, the raised donut in the steel about 1.75# in diameter will lock the alum. plate in place so the aluminum would have to tear out sideways it can't slip since it will actually be slightly 'dented in'. Don't have enough force to keep the alum from slipping and then you drop down from 0.27 to 0.062 sq. in. of cross section of alum holding things back. a nearly 80% drop in the capability.

Anybody else starting to see why BMW decided to use a TTY solution to ensure the clamping force? The design (to me is clear now) is to protect the car/frame from damage in an uneven front impact (though would also help from rear impact as well).

I only have gear that can pull 1T, maybe with a sheave (pulley) i can double that, i might see if 2T will pull the plate sideways at what torque on the bolt. I also can't wait to examine the plates on mine and wife's car to see if there is a permanent 1.75" dent from the clamping force. (if I was bmw I would stamp in a dent and then that greatly reduces the need for the extreme clamping force).

There is more function to the plate than above, clearly since i can feel the wobble in the suspension when i don't have the plate on it tightens up the front end, but i'm pretty confident that for that purpose the bolts can be FAR FAR less tight; even if the bolts slipped under stress of cornering etc, they will act like a shock absorber taking energy out of the equation.

So BMW could have just explained in a sentence "we require replacing the single-use bolts to ensure the maximum clamping force required to ensure the design strength is maintained during an accident".

Minor irony alert: the plate makes your life more at risk; anything that makes the car more rigid to protect the car pushes that force onto the contents of the car; deformation of the frame is the best way to save people. So now ya don't know what to do! loosen the bolts to make you safer in an accident or properly tighten them so you don't have to replace your car from a minor bump into a post.

It took a few days to track down that answer; they are in-fact TTA/TTY just like the E53 and I believe for the reasons mentioned above; mostly to protect the car from dynamic parallelogram loads. The forces quickly 'go off scale' when even a minor bump is involved.

The full answer is here

The exact same procedure is called for: 56 N·m + 90°

The mechanics, either pro or semi-pro that 'just reuse' without the understanding of why are doing their customers a disservice. That is not professional in my opinion. They don't know why they are supposed to be so friggin' tight and make the assumption BMW just over-engineered it and re-engineered the car to have 80% less capability in that one little thing.

I'm going to see if my local junk yard has any crashed E53 and take some measurements. It's not a stretch of the imagination to say that any crashed 15 year old X5 has almost certainly got re-used under-torqued bolts, i can even test for that if i can find one.

If my contention is valid, I should find some parallelogram shift on just about any offset front impact X5 (with the expectation the bolts have been reused and not properly torqued).

Any holes in my logic guys? It does happen, but I think i've stumbled into some solid arguments and basically 'the only reason' for this thing to be so damn strong. I was confused when i came up with 3000# twisting force from a real-world driving example, but when i looked at the diagram of the front subframe and saw it looks like a "U", things started to become clear.

I thought it might be interesting to go back to the first posts of this thread, and found this query. I found a specific directive from BMW during my search that mentions the NUTS are also SINGLE USE.

paraphrasing: "since the nuts are self-locking type, they can't be trusted to engage and lock on reuse"

however, there is a more important reason, covered by this document from Fastenal, that describes how the NUT stretches during installation and the threads engage differently the second time. (this greatly throws off the torque to tension numbers).

So IMHO, it's actually more important to replace the nut than the bolt (at least for the first five uses; I would not use the bolt more than 5 times, and I will be actually using 12.9 bolts that don't need to be stretched to yield to get the same force).

15 pack of clone bolts are here

So, probably should replace the nut even if you keep the bolt or it throws off the torque to tension ratio dramatically.

So it would seem the factor that changes the torque required the most is the nut. Learning new things every day. So, i'm thinking i'll be using NORMAL nuts and locktite and i'll replace the nuts rather than lubricate them, but the final solution will depend on the with or without lubrication and using new nuts.

On the other hand, i just found the T-slot nuts that are 12.9 to match my upcoming 12.9 bolts, i'm hoping i can get them to fit up top without room to turn so they are self-stopping no need to reach up to hold the nut.

https://www.youtube.com/watch?v=fvzdehnJA9k

I'm trying to stay out or at least limited here, but here are some general and specific comments. Not trying to give any answers, just information for those interested.

There is a ton of bad info on the internet. It's a challenge to sort through some of it.

Stress-strain of steel (and other similar materials) is a very important and pretty well studied and understood science. Important for it to be well understood for building bridges, pressure vessels, pipelines, etc.

That science can be extended and applied to help understanding of the specifics of threaded fasteners - nuts vs. bolts, yield, proof load, torsional vs. axial stress, etc. That's where things can get a little complicated and it may seem to be purely empirical and more black magic than it really is. Thinking back to the basic materials science of stress-strain helps bridge the gap.

For example, "yield" means some of the steel plastically deforms, which is a permanent change in shape, and strengthens the material. From that point on, it can still function elastically, including returning to the previously reached deformation point repeatedly in an elastic state, with the same elastic modulus but a now higher limit before yield will occur. But pushing beyond that point has its limits, and will eventually lead to fracture.


Those were the general comments. Now for some specific stuff:

Be careful if torquing with a non-flanged nut and bolt. The BMW ones are both flanged. Due to the increased area and torquing radius vs. non-flanged fasteners, and the fact that about 50% (depends, of course on surface prep, smoothness, etc.) of tightening torque is used to overcome that surface friction, using non-flanged fasteners will provide more stretch (and I use that term without distinguishing between plastic and elastic deformation) than will flanged ones.

Similar to how using really well lubed surfaces and threads might result in excessive tightening.

So that could mean if you're using non-flanged fasteners, even on the initial installation you are over torquing the 56 Nm stage, possibly causing plastic deformation where it would otherwise not occur.


Different thread pitch
If you try using SAE fasteners or a fine thread, the bolt stretch you get from applying a 90* angle will be different. The torque will be different too, but that is less clear.


Variable nut-thread loading
That is a basic fact of threaded fasteners. It happens regardless of any plastic deformation.

Fasteners are generally designed to one one hand have the nut be more compliant than the bolt to allow for better load distribution, trying to reduce this effect.

And on the other hand, the nut is always designed to be stronger than the bolt. The reason for that is that a nut would fail by having the threads progressively strip out, vs. the bolt would just fracture. You need to worry about the first nut thread stripping out, because if it starts to strip it will pass that load down the line and all the threads will strip out. Vs. the bolt fracture would most likely happen during assembly which is not such a big problem, vs. having a nut progressively strip out would happen literally "down the road" when it would be more of a problem.

For similar reasons, you should never use a weaker nut than bolt if there is any concern for nut failure. So using a 10.9 nut on a 12.9 bolt is not something to do casually. Doing that, you will be ensuring that the nut will fail before the bolt, which is the opposite of what is safer. Here's a pretty good reference for that and other things: Frequently Asked Questions on Bolting Matters

On the other hand, my M54 engine uses Class 12.9 head bolts, which do yield along their whole 110 mm length, threaded into an aluminum engine block ... or during a typical head gasket repair threaded into a ~15-thread long steel insert, which is probably not Class 12.9. So if it's designed carefully, it can be made to work.



When terms like plastic deformation, yield, proof, ultimate, etc. are used, they sometimes refer to total system failure (like "ultimate tensile strength" tells you when the bolt will snap [system failure] when increasing load is applied).

And sometimes they refer to localized material effects - where for example, the first thread in a nut may plastically deform very slightly - and it's not a problem at all, but it did deform. BTW, by the time the nut threads noticeably plastically deform, the bolt will have deformed a lot more.

True "stretch bolts" or TTY bolts - by which I mean bolts that are made specially for a TTY application, rather than regular bolts that are used in a TTA/TTY(?) application (as we have here) - are typically designed with relatively oversized heads and threaded sections, but with a long, thinner, uniform portion that is designed to yield, and to have all the yield there, and none anywhere else. Those are easier to analyze.


On figuring out whether your previously used nuts and bolts have deformed enough to significantly affect reinstallation by requiring more torque to overcome the bad fit caused the deformation ...

One pretty simple test is to see if you can finger-thread the nut onto the bolt. If you can do that, your torque wrench will probably not be fighting too hard to overcome that, and the measured tightening torque will have the same clamping effect as when they were initially used.

great stuff, especially how of course the angle changes directly with respect to the thread pitch when using TTA; the specs are only for one exact bolt. Also with the details about lubricate torque; my 'torqueometer' shows both the dry and lubricated torque.

re: hand thread nut; of course with these nuts you can't hand-thread them because they are oval in the center self-locking nuts, so you won't be able to tell that way. I was concerned that the squashed nuts would affect the torque numbers but i guess once the nut gets started it's much easier to turn because i got no reading on the torque adapter from the nut before snugging tight.

I'm a little confused by the 'stronger nut' vs. Fastenal quote above saying that the nut is 'softer' I believe that means that the metal of the nut is a lower ksi than the bolt, but because the nut 'melds' into the bolt it holds stronger or something, i would love to have some clarification on the seemingly contradictory things.

Thanks guys. Keep the info coming. Definitely going to measure my bolts when I drop my plate to do the front diff fluid.

Buy new bolts/nuts. :thumbup:

On a 17 year old X I would absolutely start with new bolts. I would not buy official BMW bolts I will be getting black oxide 12.9 and washers. If they fit I will likely get the T nuts and epoxy them in place to convert my e53 to act like the new e70 that has threaded inserts in the axle support.

Once replacing the bolts I'll be simply set I'm opting for the forever 12.9 bolts.

If I got the 10.9 bolts I would torque to spec and keep track of the use count with a center punch and dents in the plate, replace after five uses or when torque drops below about 97 N·m before 90°

(That number might change higher or lower once I test with new bolts).

I linked above to a 15 pack of decent bolts for $17.

My determination is that the high force on the spec of the design is mostly for the well being of the CAR in a crash. The bolts can be at 1/3 of design spec and handle anything you can possibly subject them to by driving. That is why "everybody" gets away with treating the metal at if it's just for under belly protection and not an important part of the frame

Cant believe this discussion is still going on had to unsubscribe as this has become as painful as an oil thread

Carry on

Would a subframe connector at the back of the "U" resolve that desire to twist? I have not checked clearances or anything down there but was just thinking out loud.

Interesting theory as well due to the many different variants of the plate. I think there are 3 or 4 total part numbers for the plates with i6's, v8's, early models, diesels, and late models all getting different versions. And to add to complication some (like the 4.8is) have steel plates while others have aluminum. The latter of which, with the large access holes cut in them, don't seem like they'd off much protection against twisting or deformation of the subframe.

The plate will not do a lot to mitigate torsion of the frame since it's straight across the bottom. It's the diagonal connections that matter. It resists a parallelogram force that would push for example the left of the car forward and the right of the car backwards in addition to keeping the back of the subframe from moving toward and away from the center.

Many cars use a giant "X" made from stamped steel but BMW chose a thick alum plate to add in underbelly protect and airstream improvement as well.

:dh:

This is an automotive forum. :D Things are bound to go circular from time to time. Is what it is. :dunno:

oldskewel and Andrewwynn
Thanks guys for the input and fact based insight on these bolts. It is always a welcome sight to read your posts. There are only a handful of regular posters who actually understand that sharing standards, insight, analysis, and "TESTING vs guessing" actually provide tips on keeping these X5's on the road.

Thanks!

It's a 20 yr old discussion but a couple weeks old to me. I found no obective input to help determine one way or the other what is going on with these bolts.

What I've detemined is that the vast majority of people including pro mechanic have been deciding without knowing what they are doing to reduce the effectiveness of the bolts by a factor of four.

I like to figure out why something is done before I reengineer it in case there's a reason for the design in the first place.

I'm planning to do both a torsion and parallelogram experiment before I put wife's plate back on.

@bc: doesn't have to be the same bolts to have the same rules, any bolt that is over torqued would be in the same line of reasoning.

Correct

No problems *yet*; the 56 N·m is pretty close to advised torque. When torquing to 90°, I noticed that by the 3rd or 4th test, i could feel the bolt go plastic deformation pretty close to 45°.

I think you came up with a very solid compromise that I would likely come up with but basing on some actual testing not just guessing.

The 56+45 will get the bolt past proof load every time so it just means it will take more times to break the bolt; the problem is this: if you didn't get the bolt to snap during install it may just snap when you hit a pot hole.

As i've covered these bolts are not mission critical, the the worse case scenario NOT involving a crash is that the sway bar gets loose and will start banging around like hell; you'll know you'll pull over, it won't do any damage.

I'm going to test the 45° TTA and see just how much less clamp force is generated. It will surely be above spec for the bolt which is 7500# and going full 90° the math worked to 9000, so it should be somewhere in between those two which I am good with.

The 'standard practice' of 'two three taps of impact' is very close to worthless in getting these bolts to do their intended job (hold the aluminum from sliding sideways), The people that do that are installing a skid plate not a shear plate.

The point of installing them TTA/TTY is to get consistent forces in the field. BMW wants to have 9000# force each bolt when installed. Using seat-of-pants methods, as demonstrated when i removed my wife's plate, achieved somewhere between 9000 and maybe 1000 if that; her car was not protected against an offset impact; both the front bolts were from a 10MM bolt perspective 'finger tight'

as you mentioned the torque similar to wheel, that's exactly right and as mentioned above on relatively new bolts, I measured over 100 N·m close to even 120 in one case; a simple way to confirm your bolts haven't hit their useful life span is to use a torque wrench when going through the 90° swing; set the torque wrench to 100 N·m (75 ft‚lb), and if you get a click before you get to about 60° of the swing, the bolts are still usable.

I could feel the bolts start to fail 2 uses before they actually failed. On the time it broke, it broke at about 120° but it was spongy by about 45°. Using a kinder, gentler 45° the whole time, i suspect the re-use count might be as high as 10 or 20 and that should get anybody through the lifetime of their X5, so as much as it was a seat-of-pants guess to use that method, I'm pretty confident that once i actually test how many times it takes to fail a bolt with that method, it will be proven to be a damn fine guess. (It also was my first thought of how i would re-use them).

Also, odd are VERY small that any previous mechanic ever re-tightened to spec, so basically if you ever start to use 56+45 it's almost certainly 'the second use' no mater how old.

I have 12 to test just from mine and wife's cars, I re-tightened all four i put back on wife's car to 90° since I'm replacing them anyhow it would be a good test and all four held well over 100 N·m during the TTA phase and are doing their job as designed. One is broken and i lost one nut so i'll have about 10 to use for destructive testing i'm going to do half at 90° and half at 45° to get some solid numbers figured out.

The torque didn't drop below 100 until the 3rd re-tighten, so i think that's a really solid # to work with and i'll test with new bolts at some point to figure out if 95 is even ok, that seemed to be the point where the bolts started to fail. For now, a dry torque of 100 N·m at 90° worked great for a 2nd use, and I prefer to keep the design spec of full clamp force myself, but don't feel bad about de-tuning a bit to extend the life either.

The bolts start to stretch at 7500#, they are full stretch at 9000# and NEW will break about 10000#. You'd literally have to crash cars to even know the answer to how much difference 7500 and 9000 would even matter, the key to get above 7500 is you NEED to stretch the bolt if even just a little so the 45° idea is the best way to do that. The fastenal paper showed that torque value is worthless to achieve clamp force on re-use of a bolt; it took 60% more force to get to the same torque by the 4th or 5th use! tap-tap-tap with an impact is so random it'd be far better to just use a ratchet and a 'good hard tug'.

case-in-point; the four bolts i just re-used and torqued to 90° varied from about 105 to 120 N·m torque to achieve the same 9000# ish force. Each re-use the cross-section of the bolt gets smaller so maybe the first time it's 9050 the second time 9000, the third time 8050, you get the picture; it's in the same ballpark until the cross section narrows quickly and the bolt stretches very easily.

Anybody with a spare hour on their hands and wants to learn a bit more about bolts, repeat the experiment with any bolt doesn't need to be this one; I put a bolt through a socket for something to squeeze, i used a breaker bar in a vice to hold one side and another breaker bar and my digital torque adapter on the other side, and did the tighten process a few times, and what became clear was that when you get to the point of yield you can clearly feel the force drop off; every bolt will have a different set up of pretension and TTA to get you to yield but you'll feel it; the torque will climb linearly until you get to yield and then it takes the same torque to keep going, it feels very odd that it stops getting harder.

The happened at just about 75-80° the first three tests, then at maybe 60 then maybe 45, the pre-failure was very obvious and dramatic, it felt like the bolt turned to lead from steel on the last test.

So, the summary if, sure the bolts can be reused. they can even pull their design force, just about 4 or 5 times, but i'd pay attention to the torque during install, and consider the 45° method especially if you remove the shear plate frequently.

As always, thanks andrew. Very informative. Will order up some of those clone bolts and new nuts after one last plate drop as I've had mine off around 4 or 5 times since I've owned it already.

I'd be interested if someone made a X brace that replaced the steel plate as it seems it could save some weight.

Not enough weight to make it worth it.

You could take some 1" steel tube crush it flat on the ends and middle and make a functional brace you'd also want to go across the back. Then you can just leave it on. (and have instant access to engine bottom. If you don't go off road not much to loose just a little more under belly turbulence.

The plate is not two dimensional so there is some flex resistance that would be lost going to x brace.

True, maybe 10lbs going from the heavy steel plate to a lighter aluminum? But greater access is the more driving force. Would take a few removals of the bolts/nuts out of the equation for normal service I would imagine.

Thanks for reading carefully. I was hoping a few people would benefit from this discussion one day.

A few of mine can be finger threaded together, so maybe the oval self locking gets worked out too. ??? But one way or another if you've got a nut and bolt that can be threaded together very easily, then there will be no extra torque needed to overcome any misfitting while torquing it down, and it should be like new in this regard.

The few people that actually do the specs and design the manufacturing processes to meet them make it so that for example a Class 10.9 bolt and Class 10.9 nut are matched to provide the extra compliance in the nut. Use them together and you're fine. So roughly the 10 there refers to the ultimate tensile stress and the 9 refers to the yield stress being 90% of that, but actually things are a little different.

The nut will also have a bit of a bevel on the first (or more?) threads, which makes it less likely to fail. Also, the nut threads have a bigger radius from the center, so more volume, so more strength than the bolt threads they match up with.

The key is to prevent the first thread from stripping out, because if it does, it is likely for the rest of them to follow as the load that is no longer carried by the first thread is passed on.

In general though, if you consider the total effective area of the nut that would have to yield (roughly the circumference of the nut/bolt interface times the length of the nut = pi*r*2*h) vs. the corresponding are of the bolt (the cross sectional area of that = pi*r^2) you'll see the odds are stacked in favor of the nut. Those areas are equal at around nut height (h) = bolt diameter / 4 (= r/2). So forgetting the variable loading, a pretty thin nut should work fine. Vs. it's more typical for steel to have the nut height close to the same as the bolt diameter. So with the extra nut height, the variable nut thread loading issue turns out to be manageable.

And that all means that it is much more likely for the bolt to fracture than for the nut threads to strip. And that would likely happen during tightening ...

even more so because of another factor that has not been mentioned ... hate to throw fuel on this fire, but ...

When torquing the bolt, the bolt will be in torsion as well as being stretched. Those two stresses combine as an equivalent, "von Mises" stress, and will cause yield at a point before just the stress due to stretch will. After the tightening operation is finished, somehow this dissipates (mystery to me).

And when considering the torsional stress, the surface friction between the bolt or nut head and the clamping surface does not count. So the torque wrench value would need to subtract out that surface frictional torque, but not the torque due to the threaded surfaces.

But that's another factor that makes it more likely for a bolt to fail.

Still, matching Class or Grade for nut and bolt is the safest practice when there is any doubt about failure.

And if you're wondering where all of these factors go in those nice geometric-looking formulas you see in the torque tables, well it's in those coefficients that appear pulled out of the air. I love when they do stuff like that - all mathematical and physical and geometric and precise and oh yeah, here's a factor of 0.18. move along, nothing to see here. Don't ask don't tell.

Found this thread while looking for directions on how to remove the stiffener plate so I can change my gearbox fluid.

Can someone summarize the findings of this massive debate about the 4 bolts?
What torque do they need? I am going to reuse mine.

Also, are there nuts on the other side of the bolts?

There are more than four.

In summary: there is no agreement. Some reuse them, some don't. I think it comes down to personal risk tolerance. Given that the bolts yield (deform/stretch) each time they are torqued, at some point, if reused multiple times, failure becomes likely. If you are the first owner or have complete records of maintenance and you know how many times the bolts have been reused, if they have, you can gauge your risk. If you don't, you're blind.

Yes, there are nuts on the top side (other side) of the bolts. From what I've read, some of them can be a bitch to reinstall.

Torque specs can be found in the Bentley manual or at Newtis.info.

Four (4) bolts on the E83 X3.
Six (6) bolts on the E53 X5.

All I know is dealer techs re-use the bolts.

Don't worry about it. just use your common-sense.
We re-use the wheel lugs all the time.

I have taken the bolts off 4-5 times for different repair jobs and re-used them w/o any issues. I just torqued them a bit less (45 degrees instead of 90 degrees), zero issues.

Sure.

1. There are 6 bolts
2. They should be replaced every 3 or 4 times after they've been removed
3. There are 6 nuts behind the bolts (use box end wrenches to hold them while tightening)
4. 41lb/ft + 90 degrees is for new bolts (I use 41lb/ft + 45-60 degrees when re-using bolts)

The 45° method is a decent method to reuse the bolts. The torque to angle spec does TTY. If you use the new bolt spec they are damaged on the 3rd use and will break usually by 5th

They are 10.9 bolts. If you use 12.9 and torque just right you can achieve the same clamping force unlimited times

Turns out, I can access the gearbox by just removing the 3rd plastic plate.
No need to remove the stiffener plate at all.

Which repairs require removal of this plate in the first place?

1. Sway bar bushings
2. Front diff fluid
3. Xfer case fluid
4. Motor mounts
5. Oil pan gasket
6. Front drive shaft servicing (guibo, splines, etc)

... and many others. :)

Finding oil leaks

Thx for the list! But, #3? I thought i saw my transfer case BEHIND the gearbox, almost at the center of the car. If so, that was nowhere near the 2nd metal plate.

You're right. Sorry. Not needed for xfer case fluid.

Good summary! Included in personal risk should be the acknowledgment that the position of BMW is wrong even though we don't know the basis.

The bolts wont be stretched using the modified torque method decribed by cn90. I don't remember what the torque values were at half the torque angle and lower preload. I seem to recall on the order of 90-105 N·m of torque to get to spec but they will only perform that trick twice before they deform notably. On the third application of torque to angle they were stretching without adding more tension and usually will snap on the 4-5th time.

BMW uses this method to achieve a consistent clamping force of roughly 9000#

Using the modified torque procedure described by cn90, you will still achieve > 7500# of clamping force which is spec for the 10.9 bolts at 67 N·m torque.

The problem with using torque to tighten is the clamping force will drop significantly each re-use as the bolt to nut inteeface degrades.

Another way to look at it is this: to active the same clamping force with a reused fastener will require 10-20% more torque so how much clamping force is lost each re use when the torque is even the same.

The point of using TTY via TTA is that you get very consistent clamping force.

I'm planning to upgrade my bolts to 1/2" if I can get them to fit because I found some grade 8 T nuts which I think will hold themselves from turning up top and can be torqued normally to get the design clamp force unlimited times.

The plate is a structural part of the suspension which is how it ended up with the crazy bolt situation. You will lose body torsion strength and rectangular rigidity if the bolts aren't tightened close to design spec.

Problem solved!

Class 10.9 flange nut, coarse thread $0.62 ea. https://www.belmetric.com/coarse-c-3...10-p-6824.html

$3.72 for six.

Class 10.9 10x55 coarse thread flange bolt $1.02 ea. https://www.belmetric.com/10mm-c-2_1...c-p-14323.html

$6.12 for six.

That's $9.84 for bolts and nuts before tax and shipping. At that price, even if I was inclined to reuse the bolts, I'd buy these new and use them. Hell, I'll probably order two sets, so if something comes up and I need to r&r the plate short notice I'll have a set on hand.

For the record, they are
M10X1,25X24
correct ?

No. 10x1.5x55 Class 10.9 flange bolts with flange nuts

onthefence owns an X3 - not an X5. This makes some of these post very confusing...

onthefence, you know the E83 is a TOTALLY different beast from the E53, right?

The E83 X3 was designed and bulit by Magna Steyr in Austria, while the E53 X5 was (partially) design and built in the USA. They share many parts, including the basic engines in some cases, but are more different than similar.

So the correct answer about the reinforcment plates bolts for an E83 X3 is M10x1,25x24 :thumbup:

Best to use RealOEM and your VIN to confirm parts etc. and newtis.info to confirm torques and procedures - don't assume that what goes for the X5 also goes for the X3.

I think the X5 uses M10-1.5x55. That's from memory though.

At least one of mine is about 24mm after five cycles of torque to angle though :-)

Always best to add year and model of your X5 to signature so input is specific to what you own.

For the E53:

Threads, rating: M10 - 1.5 x 55mm, class 10.9.
bolts: 16mm hex head with captive flat washer. BMW PN: 31101096987
nuts: 16mm hex nut with flange. BMW PN: 33306760587

Things like a flange bolt vs. a captive flat washer will make a slight difference, but it would not bother me. If I ever found that mine were not re-usable to my own high standards, I'd replace with non-BMW fasteners that fit the most important parts of the spec (size and class).

Did you end up using these? The links are dead but I'm going to try to find equivalent hardware. I'll be putting the plate back up and it's the fourth or fifth time for these bolts. I didn't want to reuse them the last time but I did.

$173.21 for 6 bolts and nuts. $22 for one lousy bolt .. what the hell is going on. I can't believe what I'm looking at.

I guess they start to sell a lot of these because people wanting to replace them every single time. So crank the price up.

I'll go read 25 pages of this, but there should be a nice kit by now.

Yes, I did use them. They worked great. The one thing I had to do was get the captured washers off the stock bolts, drill them out slightly and put them on the Belmetric bolts. The Belmetric washers were not as wide. After I got these I looked further into it and at the time Belmetric carried class 12 bolts. Figured if I needed to replace these some time in the future I'd order some. Those shouldn't deform like the class 10's under full torque. Could reuse them virtually forever. https://belmetric.com/

WFHV10YLW

BTP10X55BLK

WNORD10

NRHH10BLK

I bought enough for both of our e53 and a couple spares for $65 with shipping.

BMW crushed the nut into an oval to make it locking I ordered nordlock washers instead.

12.9 @ 80 N·m is a good match for
10.9 @ 65 + 90° (TTY)

The 12.9 at 80 N·m can be used indefinitely. Technically you'll lose clamping force on reuse if not lubricated so 60 N·m with some good moly grease for consistent clamping force.

Nice thanks guys. Andrew I read most of what you put on the past several pages, really good stuff. Thanks

I have a bunch of that ARP ultra torque I'll throw on there. I kept getting wrong numbers on the main bearing clearances until I used an ample amount of that stuff. At one point or two there would be that skipping. Surprising what a difference all this clamping force talk really makes. I'm glad we're on to page 26 on these stupid bolts.

The first time I encountered these back in December, three of them were loose/finger tight. Unknown how many times they've been used. I reused once and went the full 56nm 90°. which was wrong. The last part of that 90 felt questionable, I got lucky. So these ones are cooked.

Looks like 6 bolts washers and 12 nuts runs about $23 shipped. Which is what BMW is gouging for one bolt. Interesting. I think they want to save the supply.

There are only a couple things "special" about those bolts:

• Captive washer
• Crushed nut

You can get 10.9 bolts the correct length and non captive washers and install to spec you def don't need the blessed BMW bolts to TTY. I would recommend using Nord Lock though the amount of tension is phenomenal it likely is fine without any locking.

OR: if you upgrade to 12.9 you get almost exactly the same clamping force with spec torque. If you use molly grease you can reuse indefinitely and get spec clamping force.

Almost everybody that wrenches has gotten to that uneasy feeling of a bolt turning but not getting more difficult.

Somebody above suggested using the source jointing torque and 45° vs. 90°

It’s stunning how fast the clamping force drops off when not pushing to yield but it’s far better than “finger tight” or “two ugga dugga” which will convert a suspension part into a dust shield.

I've driven e53 without the plate plenty to know it most certainly stiffens the suspension as the name explains. Without the crazy tension from the bolts the plate will just move under the bolt heads and stop doing its job.

help, please
 

Translation needed for the four lines at the top, please.

Or better still, can you post the exact order you made for the items? It would be perfect for my wishlist.

If you put each of those in the search box at Belmetric.com it will take you to exactly the bolts/nuts/washers ordered.

Yeah sorry I didn't have the time to make links. I copied from my invoice email.