Ball nuts sheared off

[cornish wood burner]

8.8 tensile nuts,

I never even knew that that's what the number ment, time to visit the fabricator

As Bob says gussets and more bolts. Your problems would be compounded bolting through box unless you sleeved it. Any flex in the box would reduce the bolt preload and allow movement leading to a fatigue failure.

[old hand]

8.8 is only normal strength bolts 10.9 is high tensile

[Justme]

I would think that the main factor is that you are using what is basically a lorry to tow a car type trailer. It puts huge loads on the trailer & ball that it is just not designed for.

[monkeybusiness]

Make sure everything is tight too - you don't want any movement at all on those bolts.

[Stubby]

8.8 is only normal strength bolts 10.9 is high tensile

 

High tensile means they are strong in tension not in shear . If as suggested it is a leverage thing then some of the force is in shear .

[woody paul]

Weld the bugger on as well, Belt & Braces .

[Welshwoodsman]

Those couplings need to have 4 mounting bolts as well- dixon bate specify that 4x mounting bolts must be used at all times.

[carlos]

I would think that the main factor is that you are using what is basically a lorry to tow a car type trailer. It puts huge loads on the trailer & ball that it is just not designed for.

 

i dont follow you on this ??

 

carl

[Justme]

i dont follow you on this ??

 

carl

 

Its a well known problem.

 

The suspension is much harsher on a lorry. So the loads applied to the trailer are higher.

 

Think of it this way. A seesaw with almost even weights on each end. You can raise & lower it & the forces stay similar.

 

Now put a huge load on one end & a small one on the other. The small load will get accelerated about by small movements of the large load.

 

I think it came to light when caravans were towed behind recovery trucks when the tow car broke down. I have a vague memory that they developed a hitch for them to reduce the shock loads.

[Gray git]

Dixon bate do a version which has a form of shock absorber in the drop plate which was marketed as good for towing horse boxes as gave a smoother ride, might be worth looking at a bit more.

 

http://www.dryadarb.co.uk