i agree MW,a very sensible idea if vehicle been in someone elses hands.
A place i know make it a contract of servicing that you check your own wheelnuts 40 miles after collection.
Not a putdown sandygirl just an observation by the way,glad you are alright.
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It is one of the recommended preflight checks prior to towing.
It also sounds like it was fitted with things to stop the nuts coming undone, are these still present on the other wheel?
I don't think you'll have much chance of a claim, as it has been left unattended after leaving the garage, anyone could have tampered.
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Now this is one thing I am an authority on!! The money is on it being the nearside wheel.
I lost two nearside wheels on my last caravan in a 12 month period. The common denominator was disturbing the rims and nuts.
Having competed in rallying and done all my own mechanical work I do know how to put a wheel on and use a torque wrench which on both occasion I had done. The first time I was lucky to get away with minimal damage within two miles of home. The second time it was about 50 miles before the wheel came adrift and that time I had those red plastic nut braces on. The damage was much greater this time and the van was off road for 5 months. Caravan repairers are not as slick as garages.
The second time was an insurance job and when I informed the insurance company the guy I spoke to said that if he had £1 for every wheel that had come off he would be a rich man; reckoned the industry had looked at the issue and not come to any real conclusions.
The secret is to travel a short distance eg a mile, check with a torque wrench, travel say 5 miles and re check and then say 10 miles and re check. If the nuts stay tight they will be ok.
You will probably find that in your handbook it states that if the wheels have been disturbed then they should be re checked after a certain distance thereby exhonarating the dealer/garage.
I do not know wether its of heat or poor tolerences in the manufacture of wheels/studs/nuts or a combination.
On thing I know is that you do not have the same carry on with car wheels. I have become paranoid about the wheels on my van.
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Fullchat
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Rather than those useless red things it'd make more sense to fit the nuts with the green arrows used on commercial vehicles. You can see at a glance if a wheel nut has moved.
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Rather than those useless red things it'd make more sense to fit the nuts with the green arrows used on commercial vehicles. You can see at a glance if a wheel nut has moved.
Alternatively, simply use a blob of paint; I do this with the axle hub nut on my Hornet 600 motorbike.
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If this is as common as is being said I'm surprised that some kind of nylock wheel nuts are'nt available.
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Not sure Nylocs would make a difference, it's due the nut/rim seating settling down.
AFAIK everyone says recheck wheel nuts after 50 miles with a torque wrench, I ALWAYS do, especially alloys although steels are just as bad. I can't believe that people drive for miles "after feeling a problem", although seeing the state of some of these things I'm not surprised. If these wheels are the ones where the plastic trims are held down by the wheel nuts then that maakes it worse. As for the plastic covers to show the wheel nuts then they don't work if you don't look at them and obviously no-one did!
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Nylocs would'nt stop the wheel coming loose, but would stop the wheel coming off due to the nuts slowly undoing themselves. Driveshafts, ball joints etc all have nylocs (or split pins) for this reason.
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On thing I know is that you do not have the same carry on with car wheels. I have become paranoid about the wheels on my van.
Years ago amate of mine had some Weller whitel 8-spoke steel wheels fitted to his Landrover, and a wheel came off that about a week after he had them fitted.
I once had to collect a new trailer for my brothers quad bike; I can report that a wheel came off after driving 4.6 miles, driving in town traffic at 30mph, with no load on the trailer. I later found out the nuts had only been tightened finger tight on the hubs by my Dad, and the trailer fabricator (a welder mate of my dads) and I had both *assumed* they were on tight.
I would suggest its impossible to predict how long it takes for the nuts to work loose then unscrew themselves.
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One of the reasons new wheels come off is that the bolt/stud holes in them are painted and the initial tightening is onto the paint;in the first few miles,the paint coat breaks up leaving the wheel loose.Rootes had a whole team of Rally Imps lose their wheels in the first few miles of a major rally because of this.
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I've never had a wheel come loose on a wheel with disk brakes. I've had it come loose with drum brakes. My theory is the wheel studs on a disk are far removed from the not disk, whilst on a drum barked car they are mounted onto the carrier which contacts the hot drum.
Heat expand studs = lossened nut and all else follows.
No proof: just a theory..I always recheck wheels within a day of fastening out of habit .
madf
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> Heat expand studs = lossened nut and all else follows.
One of the reason Nyloc nuts can be of limited use; if the nylon melts, you are left with a plain nut. Better to use a "squashed" nut (education of correct term, please) where even quite severe heat won't reduce its safety function.
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> Heat expand studs...
Heat expands the wheels and the nuts too. If all parts are steel, the co-efficient of thermal expansion is similar, and nothing much happens to the joint.
If the wheel is alloy, it has a higher CTE, and the stud is actually stretched more when hot i.e., the joint gets tighter.
Sometimes, there can be more interfaces in a drum setup, and each interface can harbour foreign matter which can become compressed, reducing the joint's pre-load, i.e., allowing the stud to become slack.
Typically for a drum;
nut /wheel
wheel / drum
drum / hub
hub / stud
stud / nut
Typically for a disc;
nut / wheel
wheel / hub
hub / stud
stud / nut
Although I haven't done the calc, I would imagine that each wheel stud will extend by about 10 microns when it is torqued up. If there is 10 microns of crud or settling in the joint, which comresses, then, you've lost all of the joint pre-load, and, along with it, all of the torque in the wheel nut.
Back to the OP - the elongated holes only signify that the wheel has been loose at some time during its life - certainly not evidence to say that the wheel has never been tight. Once a wheel has elongated holes, it's scrap!
I'm not a great fan of locking devices which interfere with the relationship between applied torque and the stud pre-load, like nyloc, and other friction enhancing modified fasteners, *unless* the joint can be assembled and torqued normally, and then modify the friction, like staking the nuts on the rear wheel bearings of Peugeots.
Pre-load is necessary, in order to get the bolt and the joint sharing load properly - the loadpaths don't work properly unless the bolt/stud is stretched.
Number_Cruncher
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The disc would also come into the equasion as the stud passes through the wheel then the disc and into the hub.
This will be a corrosion issue, the rear of the wheel and the face of the drum.
How hot would a wheel stud have to be to melt the nyloc nut?
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About 120 degrees centigrade before the nylon lost its effectiveness.
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Thanks for that. Would a wheel stud on a caravan drum brake get anywhere near that temp? I very much doubt it. The braking efficeincy of a caravan would have to be much less that that of the car thats towing it otherwise the car / caravan combination would swap ends under heavy braking.
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Thanks for that. Would a wheel stud on a caravan drum brake get anywhere near that temp? I very much doubt it. The braking efficeincy of a caravan would have to be much less that that of the car thats towing it otherwise the car / caravan combination would swap ends under heavy braking.
It's worth remembering that drum brakes are much more prone to dragging than discs.
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L\'escargot.
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It's worth remembering that drum brakes are much more prone to dragging than discs.
I've read articles about drag racing high powered american cars that have been retro fitted with drum brakes as they have less drag. If tha caravan had a dragging brake would'nt that have shown itself when man handling the van on to the towhitch before the journey?
I've seen rally car crews change a puncture mid stage without gloves on.
Has anyone lost a wheel on a brand new caravan (with no rust between wheel and hub)?
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>>The disc would also come into the equasion as the stud passes through the wheel then the disc and into the hub.
Hmm, this is true in the vast majority of cases.
When writing the post, I was thinking of a car I had been working on recently where the disc fastens onto the back of the hub; the studs didn't pass through the disc.
I'm not a fan of nylocs because you reduce the level of preload - more of the torque you apply just goes into overcoming the friction between the nyloc and the thread, rather than doing good work by stretching the stud.
Number_Cruncher
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I understand what your saying, but virtually all car manufacturers use them for safety critical components, trackrods, ball joints, driveshaft nuts etc. If caravans after a few years use / standing are losing wheels I'm surprised after market manufacturers have'nt jumped on the bandwagon.
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I wonder if the problem is greater on caravans than on cars because caravans tend to sway more? Swaying could well put a cyclic load on the wheels and wheel bolts. Cyclic loads generally do far more damage than uni-directional loads.
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L\'escargot.
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Some commercial vehicle manufacturers use LH threads on NS wheels.
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So do some car manufacturers, older 70's Alfas used to as did a fair few yanks.
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Some commercial vehicle manufacturers use LH threads on NS wheels.
Don't Rolls-Royce own the patent on this?
Anyway, the whole episode reminds me of the time Top Gear nearly killed Lionel Ritchie!
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Indeed, a lot of the older British designed trucks used an awful design, a taper seat nut, which was supposed to position the wheel and also clamp it. While this design is barely adequate for cars, it wasn't a great success for trucks - although it lasted until the early 80's!
I've lost count of the number of those taper seat wheels we had to chuck out, either because the taper was worn, or because it was the initiation point for a crack.
The better designed commercial vehicle wheels used a spigot mounting to locate the wheel - and so prevent the once per revolution alternating shear load at the joint, and then used a plain wheel nut on a flat (i.e., not tapered) seat on the wheel. So, the stud only provides tension, no shear. This design, having vastly reduced the relative motion between wheel and hub, made (costly and confusing) LH threads on the near side superfluous, and IMO was one of the bigger advances in the ongoing problem of commercial vehicle wheel security.
I'll go a little further, and say that if you see LH threads on modern designs, it's because the joint has caused problems in development, and probably isn't well designed. LH threads aren't cheap, and no decent manufacturer will allow them to be specified unless there's no other option.
Number_Cruncher
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In the cases you mention, there has always been some kind of locking specified - typically by split pins.
Putting a nyloc on a ball joint, for example isn't such a problem because the main loadpath through the joint is through the taper. Or put another way, the only purpose of the nut is to hold the taper lock - not to transmit load across the joint. The same is true for track-rods and driveshaft nuts - while they do secure safety critical parts, they aren't load bearing, as such.
If you were to specify nylocs on wheel nuts, you would also have to tell people to fit new nut every time they had been disturbed.
Number_Cruncher
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you should change nylock nuts anyway once used but i agree with your post N/C
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you should change nylock nuts anyway once used but i agree with your post N/C
Not a great cost for peace of mind and peoples safety.
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I'm the one who wrote the original message.
Spent yesterday trying to sort things out. Looks like we have got to go through the insurance company cos we can't prove the caravan hadn't been tampered with in our front garden over the past 2 weeks,although its sat there perfectly happy since last November.
But something I thought you might like to know a couple of things the insurance company told me:
Firstly, you should check the wheel nuts every 35 miles.
And secondly, the company I was talking to said they have 6 or 7 claims A WEEK where the wheel has come off a caravan, and almost always the nearside. I asked them if anybody had investigated to find why it happens, and they said no.
But why not? If we had had a juggernaut behind us, this could have been a very serious accident, but no-one is prepared to investigate and find out why this sort of accident keeps happening. That's about 350 accidents a year, that one insurance company deals with. Add this to all the other insurance company's claims, and how many accidents are we talking about here?
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Me again - the instigator of this message. I got carried away in my last message, and forgot to thank all of you who have taken the trouble to write, and help.
It has been a great help to read what you have had to say. It's given me something to think about.
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"Spent yesterday trying to sort things out. Looks like we have got to go through the insurance company cos we can't prove the caravan hadn't been tampered with in our front garden over the past 2 weeks,although its sat there perfectly happy since last November."
Who do you have to prove it too? It is up to them to prove that it WAS tampered with not up to you to prove it wasn't! However, the reverse side of this is that you cannot prove that it was the garages fault.
Are you in either the RAC or AA 'cos both of these have a legal dept. who will give you advice and help.
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Nylocks are only partially effective for the first time they are wound down the thread and should never be re-used.I would not use them for substantial Tq loading,especially on road wheels due to the Nylon content.Better option is to use a "Stiff Nut", appears slightly Oval pinching the thread .If you are Tq loading any nut to a given value remember to add the "Run Down" torque, which is the Tq required to turn the Nut with 2 full thread showing, i.e the nuts in safety.
All nuts/ bolts will come undone unless then are locked with either a Tab Washer, split pin or positvely wirelocked.
The majority of flight critical components using a nut/bolt on Aircraft have some form of secondary locking to prevent inadvertent seperation.
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OP, didnt mention anything to do with self locking nuts.
Point was, why the wheel come off,Not an easy explanation as to why,1 reason could be the wheel studs had been greased before wheel replaced on a check,nothing unusual in that except they should be left dry, either standard grease or copper slip/grease has been known to be applied which can cause nuts to loosen
grease on a wheel nut/bolt is not a good idea,though some still do this for some unknown reason?
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Steve
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Normally ,getting the car back from a tyre fitters, I have to get a 24" breaker bar to get the wheel nuts off I thought all garage 'apes' did them up like that!
Looks like some places employ wimps!
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grease on a wheel nut/bolt is not a good idea,though some still do this for some unknown reason?
Simple,when left dry for a long time they can become almost impossible to undo,especially the sort that leaves thread exposed outside the nut.I have never had any nuts come loose on coppergreased threads.
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All nuts/ bolts will come undone unless then are locked with either a Tab Washer, split pin or positvely wirelocked.
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No, I disagree. A well designed joint is secure without secondary locking. Secondary locking is there just in case something goes wrong - dirt in the joint, too much friction in the threads meaning insufficient pre-load, more vibration than designed for because of a failure elsewhere on the system (think blade off type windmilling vibration).
I agree that there are some joints which are very difficult to design without excessive risk of fastener failure, but nowhere near as many as some people think.
The majority of flight critical components using a nut/bolt on Aircraft have some form of secondary locking to prevent inadvertent seperation.
Yes, but during qualification testing, these secondary locking features are **not** fitted. Parts have to qualify without secondary locking, and without any loss of torque/preload.
Secondary locking is just as its name suggests, an extra safety feature, not a necessary part of the design to be relied upon for safety, but a safety backstop in case something else goes wrong.
------Back to the OPs problem-----
I would imagine that an investigation into caravan wheel security would come back with a number of findings, among them;
* Typically poor design of wheel mounting and poor fastener design
* Poor control over fitting and tightening procedure
* Poor post fitting inspection and re-tightening
* Poor owner understanding of the need to re-torque
Number_Cruncher
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I have found this website (with which I have no connection) to offer valuable information when dealing with bolt problems.
www.boltscience.com/pages/info.htm
Number_Cruncher
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Very informative!! Seems to answer the question.
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Fullchat
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The majority of flight critical components using a nut/bolt on>> Aircraft have some form of secondary locking to prevent inadvertent seperation. >> Yes, but during qualification testing, these secondary locking features are **not** fitted. Parts have to qualify without secondary locking, and without any loss of torque/preload. Secondary locking is just as its name suggests, an extra safety feature, not a necessary part of the design to be relied upon for safety, but a safety backstop in case something else goes wrong.
Don't know about that, but by your argument a company quantifys a bolt without a split pin hole, and then drill it to accept a split pin it ensure its secondary locked, thru a castelated nut. Having done this they re-do all the validation/ stress calculations:.
I don't think so more like they design the assembly take into account secondary locking then run then qualify it.
Lost count of the manhours i've spent wirelocking rotor head lower pressure plates not just 2 bolts but all 32 of them with 1 piece of locking wire.
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Hi bikemade3,
Sorry, perhaps I did not explain and express myself very well.
Aerospace parts are, of course, designed to be wirelocked, split pinned, or whatever when used in a flight application.
But, during the qualification tests, the secondary locking is not fitted - this allows you to check that fasteners remain tight by proper design rather than remaining tight during say a vibration or a mechanical shock test just because of the secondary locking. Otherwise, it would be possible for secondary locking to disguise poor joint design during qualification testing.
This procedure isn't just company specific, it is standard aerospace practice to guard against what are known as dormant failures - i.e. failures that you can't detect because they are masked by another part of the system.
Then when the design has passed qualification testing, and the parts go out to be fitted to aircraft, the locking is put in place as you describe. In this way, secondary locking truly behaves as an extra backstop; an extra layer of safety.
Number_Cruncher
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>>This procedure isn't just company specific...
Although I might be wrong about this, it's some time since I did any of this type of work; I think the relevant document where environmental test specs and procedures are defined for airborne components is RTCA/DO-160
Number_Cruncher
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wire lock is ideal any situation eg
if you whip the top of say a 2000E gearbox you can identify the weak link immediately
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And secondly, the company I was talking to said they have 6 or 7 claims A WEEK where the wheel has come off a caravan, and almost always the nearside. I asked them if anybody had investigated to find why it happens, and they said no.
Why not find out the opinion of The Caravan Club? www.caravanclub.co.uk/
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L\'escargot.
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Food for thought in this thread. As a caravanner for the last 20 odd years I have yet to have wheel coming off/loose problems. However, I was interested in the fact that on the last 2 occasions that I have had my van serviced I was not allowed to move the van without the mechanics insisting that I watched them apply the correct Torque to each wheel nut. They showed me the recommended setting, showed me as they adjusted the torque wrench and made me watch as each nut was tightened. Certainly suggests that they are aware of a "problem"??
In future I will check before each journey.
Thanks for the info.
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Phil
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Hi,
I'm the instigator of this message.
Thank you all for your help, its really appreciated, and I've learnt a lot this past week.
In reply to a couple of postings - I've looked on boltscience.com/pages/info.htm and it's really interesting. I shall certainly be showing it to hubby.
I've also been in touch with the Caravan Club Legal Dept. They say we can't prove 100% that 1. the caravan wasn't tampered with on our front drive, and 2. we can't prove the tyres weren't tightened properly when it was in for service.
After what I've heard this past week about bolts coming undone on their own, I don't think I have a strong case to take it to court.
However, the manufacturer rang on Friday, and was as nice as he was unhelpful earlier in the week. He's going out of his way to get our caravan back on the road as soon as possible, and offered to pay our insurance excess for us. You can't get fairer than that.
He told me he rang the company who make the little pink things which go over the nuts, and he was amazed to find they wont stop the wheel coming off, they only hold the wheel on longer. He was of the opinion they would hold the wheel on, so he learnt something new as well. He said Bristol University had done research to try to find the cause of wheels coming off caravans, but they never came up with any concrete reason. But I did find the boltscience.com site very explanatory.
So if you see a little folding caravan travelling along the road at 30mph, please don't swear or shake your fist as you pass, give a wave instead - it'll probably be me driving cautiously!!! Or perhaps someone else who has lost a wheel!!!
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On a recent trip down the M1 we came across someone on the hard shoulder with a yacht on a trailer - and yes the nearside wheel appeared to have come off. Coming back 6 hours later he was still there. The RAC was with him so I could only imagine they were trying to find a wheel from somewhere to get him moved as the trailer wouldn't fit on an RAC pick up truck.
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