Hi 

No experience of this directly. But as a fitter mechanic with wide experience I have never had nyloc nuts come loose. What usually happens is the pieces bolted together crush and give way. This look like the nuts came loose but after you tighten them several time it becomes obvious it is the collapse of the bolted pieces. Not sure what you did in the change but perhaps the A frame channels need a spacer to take the crush load. 4x grade 8.8 12mm bolts and nyloc nuts will support a big load themselves. 

Jaahn

 

Thanks Jaahn, iana,
There is/was nothing to crush. The mounting plate is 8mm thick (welded to the bottom of the A frame), then there are 2 levelling plates 25mm thick & then the hitch which is cast iron. I might get a couple of longer bolts tomorrow (two are long enough) & add some locking nuts - just to be sure. I'll ask about the radiused washers too.

Previously I was under the belief that nyloc nuts did not move.

Mezza, the chains side of it has no bearing on my situation but it might be a handy reminder to others who read this posting. I've seen some odd lots of chains used in our travels - including some who were "newbies" & weren't told to cross the chains.
I noticed there were 305 views & only 2 replies to my query!

The radiused washers, and bolts that were radiused between the shaft of the bolt and head are aviation parts, don't bother asking. Why don't you just buy a new set of bolts, washers and nuts, fit and forget. Another thing to check for when fitting, is the length of the bolt, make sure the bolts are not too long, and the nuts are not binding at the end of the threads before the parts are tensioned up properly. And another point again, I would fit the bolts up from the bottom in this case, so that there is only bolt shank passing through between the plate on the "A" frame and the hitch.

Bulariver wrote:

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I recently had a slightly scary experience - we free-camped for about a week and the van was not taken off the tow-ball over this period. When I did take it off, I found the large nut that holds the tow-ball on was very loose - it had vibrated down about half a centimetre - hate to think what would have happened had it vibrated down more and fallen off! OK, I know I should have checked it daily but we are humans! It's tight now but I have learned a lesson. Here's a question for the experts - does the tow-ball have a life and should I replace it - does it suffer from metal fatigue? Cheers, and remember, check, check, check!! Bula

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 YES it needs replacing, it will likely have hairline cracks

cheers

blaze

iana wrote:

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Bulariver, there could be a couple of issues here. If you can imagine what that tow ball was doing every time you accelerated, or applied the brake. So what condition is the hole in the tow bar tongue, is it enlongated, or flogged out? what about the surface where the flange of the tow ball sits, and the surface where the nut sits, is that worn (unevenly), the there's hammering that the bolt of the tow ball has been through. The bolt itself will fatigue a bit like putting a nail in a vice and bending it back and forth, it will break but when God only knows.

And I guess that is why we have chains as a backup safety measure. If I were you, I would replace the tow ball with a quality unit, and maybe the tongue as well.


P.S. what about the pin holding the whole lot to the tow bar, isn't it also receiving the same treatment. The bolts holding the tow bar onto the vehicle, Oh my God what have I said. 

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 Thanks for your advice blaze and iana. The hole does not seem to have suffered but the spline in the tow-ball shaft has taken a beating! I will replace both the ball and the pin that holds the hitch onto the ute. Do you know the best place to buy quality fittings - they have flashy looking balls (!) at Super Cheap for about $25 but I worry they are made from recycled steel in China! If I buy from a caravan repair shop I might pay double but get the same thing! Where can I buy and know I am getting quality? Bula

As blaze said, nylocs nuts are single use nuts, throw em out and put new ones on. That's what I learnt back in the day when I was doing an engineering course. You will have piece of mind & torque em up.

I missed the part about the 2x 25mm spacers, would think this has more to do with the problem than anything else.

I think that, that engineering is completely wrong. It would be better to get a tow tongue that's 50mm lower. Or to weld a second 8mm plate in place with close fit mounting holes, and spacers between the two plates. If those 25mm spacers are not welded in position, and, or the mounting holes are sloppy, some very bad strains on the bolts are going to be happening, bending the bolts and straining the heads and nuts.

Hello everyone,
Thanks for your responses.
I did wonder about the two plates - they are each 25mm thick - one for each pair of mounting bolts.
I didn't what to weld them to the original mounting plate as that would make things difficult for a future buyer of the van (if that happens).
They were made by an engineer with a good reputation in Toowoomba. I did suggest that a one piece plate might be better but I was told the two spacers would be as good.

I'm not certain of our movements from SW Victoria (would like to head north where it's a bit warmer). With family issues at the moment, we may be heading back to Toowoomba instead of Bowra/Bladensburg - if so I'll go & see the chap again. And I'll keep a close eye on the bolts (the fit through the original plate is not sloppy).