i'm not sure if you read the link i posted or not, but it clearly states how jam nuts work and simply installing the jam nut over the existing torqued fastener will NOT prevent self loosening. the videos are quite illuminating.

if you haven't read it, i'll summarize: the thin jam nut goes on first torqued to 25%-50% of the torque specification. then the full size nut goes on and gets torqued to specification. This will effectively "jam" the two nuts together and helps prevent self loosening. Two full size nuts can be used, so long as the first nut is "under torqued" and the second nut is torqued to spec.


as for the frame condition, i guess i'd say it is typical for a vehicle around here of that age. We use salt, and lots of it. and it sits out and is never garaged. Which was part of my angst with the failure i had on my air bags. i stand firm in my feeling that they are not considering all environmental conditions in the selection of their hardware.

For a non-load bearing fastener, stainless steel should be used, IMO. for load bearing, plated fasteners should be used. using high strength bolts adds a margin of safety which lower grade fasteners do not.

to the bridge connections. yes they are driven to a very high torque, but it is within the working range of the bolt. that is to say, when loosened, the threads would not be distorted. In our state (along with most others), we do not use torque values as they are an inaccurate indication of axial clamping force (which is the whole point of a tensioned bolt - that is to clamp). We use Direct Tension Indicators (DTI), which is a special washer with bumps on it which flatten out under the clamping force of the bolt. When the bumps are compressed to a specified gap (0.020" usually - checked with a feeler gauge) then the proper bolt tension is achieved. for those curious:Direct Tension Indicators (DTIs) by TurnaSure

And yes the splice plates are huge with lots of bolts in it. but that's what i say by "properly designed" these vibrational forces are known and this is why the plates are so big with so many large bolts. it is all about surface area and clamping force to prevent the splice plates from moving under vibration.

why do i bring all of this up? and how is it pertinent to the discussion?

The fact that you have eight 5/8" bolts holding your hitch to your truck is a pretty good indicator that there is not enough clamping force to prevent movement of the hitch-frame interface. Bolts self loosen when the connection moves, that is HOW the bolts loosen (again, the videos in the links above are quite enlightening). If a problem is encountered, additional measures should be taken to prevent this problem going forward. Which would include new hardware of higher grade (if available) torqued to the specified value for the grade of bolt being used (belt). Jam nuts would provide some additional resistance to self loosening (suspenders).

All that being said, most times it is not a problem. but when it is a problem, it can be a BIG problem.... as illuminated by the OP.

i guess my only point was, if you are going to do it, there is a right way and a wrong way ... whenever possible, do your best to do it the right way, and eliminate as many points of potential failure as possible.

mike

 

I dug a little deeper on the spring washer info and there are a couple of videos in this link: Helical Spring Washers

It does look bad for the spring washers though really don't know the parameters of the tests - so don't have a good feel for how they came up with that proof. Yeah, I could possibly dig a little deeper and might find some more, though would like it shown with star washers as well. This series of videos with and without locks is pretty inconclusive without more information plus I get the feeling they are trying to sell their product. As far as star locks, decent ones are hard to find locally though I used a lot when I built my '31 Ford roadster, purchased from McMaster-Carr.

The torque til the t1ts are flat locking washers - kinda new product, looks good and a lot safer, but who knows how many bridges and buildings were erected using only a simple bolt and nut whanged down tightern @#$% with a mega big impact driver.

 

Well guys,
Sounds like both of you are very informed and passionate about using the correct fasteners for the right application.
Question...
Knowing that Grade 8 fasteners are heat treated or case hardened to increase strength, the also should be more brittle then.
If so, are there applications where you would be better served to use a lessor strength bolt such as a Grade 3 or 5 for a safer/better fit?

 

i detect a bit of cynicism, which is fine, but from what i can tell about the company in the link is they are consultants offering thier services to help customers find solutions to problems, not sell a product. Least wise, i could not find a single bolt, nut, or washer for sale on that company website.

as for the construction method of bridges, i can tell you that the process above was NEVER an approved method of tighening structural fasteners.

before DTI's, "turn of the nut" method was the standard. DTI's were invented to address deficiencies inherent to the Turn of the Nut - namely the largely unpredictable clamping force applied by the fastener. there was a large propensity for fasteners to be under torqued and over torqued, and everything in between.

Truth be told, applied torque suffers from the same problem as the friction force between the threads of the nut and fastener are largely unknown. If you REALLY want to make sure it is tightened properly, you need to check the amount of strain (stretch) in the bolt. In reality, for everything except structural fasteners, applied torque is "close enough".

I would also say this in response to your skeptical outlook on the referenced webpage. Everything i have read on that page aligns 100% with what we learned in structural design, AND with what i see in the current structures being built. I'd take the information on that page as being very authoritative.

Yes, depending on the application.

if the bolt will see cyclical loading then the brittleness of the bolt comes into play. Say a hitch pin. There is no tension in a hitch pin, but rather side loads. Would you want a hardened hitch pin that can withstand great forces but breaks when overloaded, or would you rather have a softer pin that bends? depends, i suppose, but most time in an application like that, you'd rather have the fastener deform than have the two pieces come apart. Stainless would be a particularly poor choice for this type of application.

if they are using the bolt to hold two pieces together, the theory is that the applied torque puts more strain on the bolt than the outside load will. That is to say that any load imparted on the fastner by the outside worlds will be less than the strain imparted on the fastener by the nut. So in this application, the bolt never sees any load other than the strain from the applied torque.

this is how nearly all structrual fasteners are designed, and how the bolts that hold your hitch to your truck SHOULD work ... now, whether they are or not is, appareatly, debateable.

 

I have many issues with the methods on that split-lock test.

First of all the obvious:
1) the nut and threaded shank don't seem to fit well. Every new fastener pair I've ever used could be spun and freewheel with very little effort.

2) preload is not a good force to measure here. Clamping pressure or bolt tension would be a better measurement. I'm not sure the investigator knows what preload is.

The not so obvious, possibly intentional:

the "bolt" is fixed. The machine appears to be designed to vibrate a plate against a fixed bolt. This means each oscillation includes a period of lower tension. There is no vibration data (amplitude, frequency). In reality, known oscillations would be induced between two plates which are fastened together with a known pressure. The bolt-washer-nut package will be free to move in space, unrestrained against each other. Clamping pressure would be monitored and logged against time.

 

I think you just said it much better then I did. Thanks

 

you'd have to watch the other videos to know this, but they are actually measuring clamping force via load cell beneath the plate.

AFAIK, the bolt is not fixed and is free to rotate such as you would have in the real world.

if you dig into the website a little deeper you can see the graphs where the clamping load is plotted against time (cycles, actually), just as you suggest.

the test is actually very well thought out, and AFAIK, was instrumental in developing a better mousetrap to solve the issue of self loosening bolts. The basic testing procedure has been around since 1969, according to the research i have done.

i get your angst with not knowing the oscillation frequency, but in all truth, i don't believe it maters any. The test is merely an accelerated means of testing what will happen to a bolt system under vibrational forces. the high frequency just speeds things up so that you don't have to wait 10 years to see what would happen.

in truth, you don't have to "like" the test, just understand that it is a standardized test with specifications, and so long as those are adhered to, then the test and results should be considered valid, and comparable to other results the test produced.

i guess one can take what they wish from the discussion, but the bottom line is you will NEVER find helical lock washers used in anything structural. why? because they do not work. furthermore, if the design is proper, and the installation procedure is proper, they are not needed.

the problem, in this case, is that there is likely not enough clamping force to keep the hitch from moving ever-so-slightly and causing a problem. think about the forces a hitch has to resist with a loaded trailer going down the road ... all the pushing and pulling that goes on over every bump, if that hitch moves even a thousandth of an inch over and over and over ... this can cause the problem outlined above..... not to mention an overload to a system that may be marginal to begin with .... lots of potential for problems to begin and exacerbate.

all i'm saying is, for all the reasons above, IMO ... there is a proper way to approach fixing the problem, if one arrives. The information i've presented, to the best of my knowledge, training, and experience, is correct and accurate. I would not have posted it otherwise. As an Engineer, if you don't know, you say you don't know, caus anything you say can, will and does get held against you in a court of law ... professional liability ... it drilled into you in engineering ethics 101, 102, 201, 202, 301, 302, 401, and 402....

that and critical path ... uuugh ...

 

frequency definitely matters. You could make the nuts and bolts come apart at an unrealistic, unnatural hyper-sonic frequency if you want, but that won't be very pertinent to an automotive application whose significant vibrations are transmitted through the suspension.

The "bolt" is apparently fixed in the video. Could be tack welded to the bottom pate, who knows. The video including the split-lock is where it becomes obvious. The other indication is that the bolt does not spin with vibration.

In automotive applications you also don't often have parts that have freedom to spin against each other. Axial rotation of the two pieces is what I see loosening the nut in both of those videos. That degree of axial rotation is not possible (before failure) of a piece attached at two or more points.

Methodology is my life right now. Creating test procedures, measurement techniques, and data acquisition systems is what I do. I will say this. The plot of the w/split-lock data is much preferred as it appears predictable, easy to design for, and repeatable. Did they replicate, or was it one shot?

 

i understand what you are saying, but disagree completely.

frequency is just movement through time. if you slowed that machine down to very low frequencies, but kept the amplitued the same, the results would be the same but would just take longer.

it is the movement that is causing the nuts to self loosen, not the rate at which the movement happens. the Junkers just speeds the process up.

now, if you were to say that amplitued makes a difference, i completely agree. reduce the amplitude, and that may well make a difference. but still, movement is movement, and movement is what is causing the nut to rotate.

what frequency do you think should be used? that is to say, what is a realistic frequency for a hitch on a truck? the tining on the road is randomly spaced with the narrowest spacing being roughly 3/32". If you were to run across those tines at 60mph, you would hit those tines to the tune of 11,264Hz... that's plenty high frequency. tines cause vibration, those vibrations have to be absorbed by the vehicle somehow, and that would include (to an admittedly very minute degree) the bolts holding the hitch to the vehicle. You can say "unrealistic super sonic frequency" but there are some very high frequencies encountered on the road.

the bolt is not fixed. the bolt head is adjacent to a fixed plate. the top plate slides on the bottom plate, and the bottom plate does not move. The bolt wont move unless the bottom plate moves, as the top plate slides about the bolt. if you were to run the bolt down from the top, you would see the bolt head moving about, whilst the nuts and washers do not move. either way, you would have the same rotating effect.

as show, the nuts rotate while the bolt stays fixed. reverse the oreintation of the bolt, and the bolt would rotate while the nuts stay fixed.

here is an excelent demonstration of how the machine works and all the priciples i am trying to outline:
http://www.boltscience.com/pages/Why...elf-loosen.pdf


again, i undestand, but disagree.

2 points or 100, makes no difference. if you have a hole with a bolt through it (or 100 holes with 100 bolts) there is enough clearance for the bolt to slide through. even if that clearance is 0.001" it means that there is potential for 0.001" worth of movement. it is a round hole sliding around a round bolt. it can move 360 degrees, thus causing the rotation seeing in the videos.

refer to figure 1 in the poster link above.

the fact that hitch bolts are loosening in the real world is proof that your statement above is not true, as most hitches i've installed and looked at have at least 6 bolts, usually 8.


i can appreciate that, and your analyitical (though skeptical) approach is evidence of that.

i guess my only real problem with the skepticism to the vidoes and data in all the links above is that you are attempting to argue with well established research and results that are currently being applied in the construction world today. this machine was the primary reason why we currently build things the way we do in the structural world today ... to argue agains the means and methods is to question all the results it has provided.

it is an admitteldy sever test, but illuminates what happens to fasteners over a long period of time. You may like the predictablity of the curve with the helical washer, but it does not show any improvement over a bolt with no helical washer ... predicting failure faster is not a good thing IMO.
(figure 6 in the link above)

why do i keep referencing the same page?
because other than that page, there isn't a lot of clearly visable data present on the web, and these guys have the best group of data i have seen, and it all appears to be accurate and consistent with current methodology.

i'm gonna stick a fork in it as i have no delusions of grandeur as to my abilty to change anyone's mind. All i can say is if someone were to ask me what to do if they were experincing a problem, i'd refer them back to post #16, where i said:

 

You missed the mark on the rotational freedom.

Two pieces attached by a single bolt are free to rotate against each other around the axis of the bolt for 360 degrees. Two pieces attached by two or more bolts are free to rotate against each other, but only as a function of the distance between the centers of the bolts and the clearance available for the bolts. (which means manufacturing flaws are sometimes good, especially when the holes are off just enough to put a shear preload on the bolts... rotational movement is reduced... Similar to the racking system used in European competition billiards). As the distance between the bolt centers increases, the possible degree of movement between the parts decreases. Likewise, as the clearance for the bolts decreases, so does the degree the parts are free to rotate against each other.

Watch this video again Video of a Helical Spring Washer subjected to a Junker vibration loosening test notice the washer being threaded onto the bolt. That bolt is fixed to the bottom plate. There is no question.

Most of these aftermarket hitch bolts loosen for one of two reasons, the first, and less common, is overloading the tongue. This puts a direct axial load on the bolts and stretches them. The other, is movement of the wax coating on the frame. Due to heat, pressure, and vibration, the protective wax coating that modern frames are dipped in will remove itself from between parts, effectively reducing the force with which the parts are clamped together. That wax should be removed from the frame wherever something new gets attached.

 

well thanks to all for the info and reading material---
so with my hitch situation obviously I need to replace the mounting hardware,
it would seem that what reese had supplied and spec'd is not adequate or suitable.

the reese hitch will accept only 1/2" bolts, frame mounting location will accept 5/8"
so do I use 1/2" or drill out and use 5/8"?

and for grade8 hardware what is a good tq spec for the respective sizes?

thankyou

oh and yes it is 8 mounting bolts,
also interesting I looked at the newest version of this hitch from reese and they have changed the hardware and specs, perhaps I should just contact them for replacements

 

i think that is the root of your problem, the having 1/2" bolts unrestrained in 5/8" holes allowing the hitch to move around beneath the frame (remember what i said about holding the nuts still while the bolt is rotating about the nut? that'd be my guess as to what is going on here.)

the safest solution would be a step washer, or step bolt that would bear against the 5/8" hole in the frame and the 1/2" hole in the hitch.

i'm not going to be the one to recommend you drill out your hitch. What i would do on my own, and what i would recommend might be decidedly different.

bad call on reese to use 1/2 inch hardware in a frame designed for larger bolts. (remember what i said about lacking in either design or installation? even a perfect installation cannot fix a poor design)

see what reese has to say, but i'd bet "you're the first one to have this problem" that they've heard of ... i.e. don't get your hopes up for too much help from them.

 

we are talking the same language. i wasn't trying to say that it can spin on an axis, but that it can move on an X-Y axis within the limitations of the clearance between the bolt and the hole. as you say the tighter the clearance, the more movement is reduced. but ANY movement can cause the nut to rotate, and that's what happens. the number of bolts doesn't matter, other than to have enough clamping force to eliminate the movement for the forces to be expected. if there is not enough clamping force, movement can occur and bolts and self loosen and it snowballs from there.

i've watched it many times, along with many other videos on the Junkers. i find it much more likely that they are holding it from the bottom with a socket, as that is how the machine is designed.

what you are suggesting is misapplication at best, and fraud at worst. that is to say they are either incompetent or crooked. what would they have to gain? the are offering professional services to people with problems, not selling anti-rotational devices.

take a look at the cutaway of the Junkers device and it is clear how the bolt is placed in the machine..... as you say, there is no question. why would they ruin their very expensive test machine by welding a bolt to it. that wouldn't make it very handy to use for the next test, i would think.

on this we mostly agree, except i'd say that hitches are much more commonly overloaded than people admit to. out of our 3 trucks, i've overloaded all of them at one time or another. not proud to admit it, but around here we got a lot of farmers hauling stuff they prolly shouldn't

in the OP's case, i'd say his problem is the 1/2 inch bolts in 5/8 inch holes. That needs to be addressed or the problem will persist.