Thread: Help please! Jackknife = trailer & chassis repair

The lunette bolts are 3/8" UNC high tensile, I would recommend replacing with 3/8" UNF high tensile, any competent hardware store should have them, or any fasteners store will. As others have said they are literally bolts with the heads cut off, those trailers are very agricultural.

Looks like a Perentie rear cross member? If is is they are fairly heavy RHS, remove the pintle and have a look at what's actually damaged, has it just pulled the nuts through or is the RHS bent? I'd suggest just plating it on the inside if needed and straightening the rear edge, then re-installing with new 1/2" UNF high tensile bolts. But with the pintle still installed I can't see whats actually mangled.

Stripping it all down would be my first step.

Originally Posted by MR LR

The lunette bolts are 3/8" UNC high tensile, I would recommend replacing with 3/8" UNF high tensile, any competent hardware store should have them, or any fasteners store will. As others have said they are literally bolts with the heads cut off, those trailers are very agricultural.

Looks like a Perentie rear cross member? If is is they are fairly heavy RHS, remove the pintle and have a look at what's actually damaged, has it just pulled the nuts through or is the RHS bent? I'd suggest just plating it on the inside if needed and straightening the rear edge, then re-installing with new 1/2" UNF high tensile bolts. But with the pintle still installed I can't see whats actually mangled.

Stripping it all down would be my first step.

Cheers thanks for the info! I am getting the local welder to weld them up but I just ordered 100mm x 10mm in 8.8 fine thread in black with nylocks from a bolt shop in Cairns, getting flown up tomorrow. Do you think that will be sufficient? I know I'm over thinking this one but would like to do it right the first time around.
Cheers
Ty

Originally Posted by squizzyhunter

Cheers thanks for the info! I am getting the local welder to weld them up but I just ordered 100mm x 10mm in 8.8 fine thread in black with nylocks from a bolt shop in Cairns, getting flown up tomorrow. Do you think that will be sufficient? I know I'm over thinking this one but would like to do it right the first time around.
Cheers
Ty

That will be even better as 10mm is slightly bigger, may need to clearance the holes but that's no biggie.

Originally Posted by MR LR

That will be even better as 10mm is slightly bigger, may need to clearance the holes but that's no biggie.

That was the plan but was second guessing after Dave was saying that it is supposed to be the point of failure when things go ass up. I suppose that just fraction more size should not make it too much stronger.

Originally Posted by squizzyhunter

That was the plan but was second guessing after Dave was saying that it is supposed to be the point of failure when things go ass up. I suppose that just fraction more size should not make it too much stronger.

I don't necessarily agree that it is an engineered failure point... more like **** poor design, but that's just me being overly critical.

Originally Posted by MR LR

I don't necessarily agree that it is an engineered failure point... more like **** poor design, but that's just me being overly critical.

Haha yes I suppose that's fair 👍

Originally Posted by MR LR

I don't necessarily agree that it is an engineered failure point... more like **** poor design, but that's just me being overly critical.

you do know that the ADF used to teach people to drive and reverse trailers right?

I've seen people that cant reverse a trailer without jacking it and busting up the draw bar and the rear cross,,,,, wait a second.....




Its bolted on for a few reasons.

the bolts break off and they are easier to grind off and weld on than welding the link on.
when the link wears its easier to unbolt one and bolt on its replacement

Originally Posted by Blknight.aus

you do know that the ADF used to teach people to drive and reverse trailers right?

I've seen people that cant reverse a trailer without jacking it and busting up the draw bar and the rear cross,,,,, wait a second.....




Its bolted on for a few reasons.

the bolts break off and they are easier to grind off and weld on than welding the link on.
when the link wears its easier to unbolt one and bolt on its replacement

I'm not disagreeing that that works... that's how I suggested he repair it also

But I highly doubt it was designed like that, never seen a design brief that says "make sure the hitch is easy to snap off!"

Willing to be proven wrong, but anything else is here-say.

Having built a few trailers though, and worked on number 5's, I think it's a crap design.

We have a very early box trailer on the farm (Ford V8 wide-5 stud pattern to boot) and it has a wooden draw bar, doesn't mean it was designed like that to self detach if your load incinerates itself

I can't believe people can't reverse trailers, it's so easy... although I did have pedal cars with trailers as a kid