Safe to use recovery strap on hitch pin instead of shackle?

[winkosmosis]

I've seen folks on forums recommend putting the recovery strap loop over the hitch pin, in place of a shackle assembly that mounts in the receiver.
But some people say that it's not safe because the pin can break, since it's not the same shear force it's meant to take.

So what's the deal? Is it safe to use a hitch pin or can it fail before the strap?

 

[Bennyhana]

I think it would be fine for a lite recovery, I've had to use that method winching a guy out of a snow bank(he had no recovery points). I don't see how much more different it is than using a receiver slug set up with a shackle. But I guess it depends on the quality of the pin. I too have seen it demonstrated as what to do instead of using the ball.

 

[computeruser]

Huh?

Explain the difference between attaching the strap to the hitch pin versus the shackle insert which is held in the receiver by...the hitch pin. I don't see what the difference would be.

 

[winkosmosis]

I found some unrelated discussion on hitch pins. http://grassrootsmotorsports.com/forum/grm/towing-hitch-pin-thingamabob/526/page1/

curtis73

Those pins are debatably fine for towing, if they are the right strength. Grades of bolts basically indicate their hardness and therefore tensile strength. Grade 2 (normal cheap stuff) you can bend a few times and still have a viable bolt for holding a picture on your wall. They're pretty soft. The one thing they don't do well is high tensile forces. The soft steel will either strip the threads or literally pull the fastener apart. Grade 5 bolts add a significant amount of tensile strength but can still take side loads with composure. They will bend a decent amount before breaking. Grade 8 bolts are very high tensile strength. They are best used in applications where their entire load is tension. They don't like to bend. I used to use grade 8 bolts through a chain link to hoist engines until I lost one. I had a grade 8 bolt threaded in the whole way into a head. It didn't bend a bit before shearing off flush with the head. I won't talk about the brand new polished aluminum oil pan or $400 radiator that bit the dust in the process.

For instance, when you see engine fasteners from companies like ARP, they often list their tensile strength. In applications like rod and main bolts, the higher the better. They never see side loads at all. Applications like hitches are a different story. That is purely shear loading.... which brings me to my next confusing part...

If you have a hitch insert, the shear loads placed on the fastener are very localized. A hard grade 8 bolt would usually suffice since the close shear tolerance prevents the fastener from deflecting. In that situation, the softer bolts migh prove problematic since they might abrade and get smooshed under those kind of loads.

So... provided the pin is the proper size for the hole, and the insert is the proper size for the receiver, all should be well. Most of those pins are listed as having a certain tensile or shear strength.

I was thinking that a grade 8 pin would be better than a grade 5, but according to that post, the 8 would be worse for bending load, which you'd have if the strap's force is focused on the center of the pin.

 

[MuddyOval]

Has anyone ever actually broken a good quality pin? I'm sure it's a bad idea to jam a screwdriver, pen, popsicle stick or whatever in there- but a good pin is really strong.
If pulling at an angle, if the receiver has sharp edges you could potentially damage the strap.

 

[winkosmosis]

Huh?

Explain the difference between attaching the strap to the hitch pin versus the shackle insert which is held in the receiver by...the hitch pin. I don't see what the difference would be.

The difference is that depending on how the strap loop is shaped, it could focus its force on the center of the pin, causing it to bend or break. It's like there is leverage on the pin, vs the shearing force from a square mount held in by the pin.

I wonder if that's just theoretical or if it has actually happened though. Hitch pins are so thick I have a hard time picturing one actually bending much less breaking, with the normal loads of recovery.. especially with the elastic recovery strap. Also though, even if it breaks, wouldn't the pin just stay in the reciever while the strap flies out?

 

[computeruser]

I believe that the grade 5 versus 8 is going to favor 8 in this instance. Sure, it might not want to bend as happily...but as I recall, while it will break dramatically, it will do so after the 5 would have distorted AND busted.

In any case, it would seem that the more relevant issue would be whether it is prudent to do recovery off of a receiver hitch in the first place, rather than some sort of bolt-on or weld-on hook or ring, attached to the frame. Right?

 

[winkosmosis]

I believe that the grade 5 versus 8 is going to favor 8 in this instance. Sure, it might not want to bend as happily...but as I recall, while it will break dramatically, it will do so after the 5 would have distorted AND busted.

In any case, it would seem that the more relevant issue would be whether it is prudent to do recovery off of a receiver hitch in the first place, rather than some sort of bolt-on or weld-on hook or ring, attached to the frame. Right?

On a Jeep XJ's unibody, a hitch is the best method since it's bolted to both sides, with nut strips distributing force.

 

[BIGdaddy]

i've done some light towing with no obstruction via the hitch pin. Worked fine.

for a yank, either getting me, or getting someone else out of a sticky situation, I'd prefer a receiver mounted shackle or something like Detourusa's kit that attaches two D-ring mounts on either side.

Either this:

or this...

 

[RHINO]

the only problem i have with the hitch pin method for a yank or hard jerk is the relatively sharp edge of the reciever tube. though i have done this several times and not broken a pin, a shackle is much stronger.

 

[I Leak Oil]

I was thinking that a grade 8 pin would be better than a grade 5, but according to that post, the 8 would be worse for bending load, which you'd have if the strap's force is focused on the center of the pin.

You are correct in your thinking. The grade 5 will be reduced to a quivelling pile of mechanical poo before the grade 8 starts to break a sweat.

I've used the hitch pin method before but the sharp edges, as mentioned earlier, do damage the strap. And it's tough to get it hooked up when it's cold and icy, packed with snow or mud.

 

[michaelgroves]

On a Jeep XJ's unibody, a hitch is the best method since it's bolted to both sides, with nut strips distributing force.

IMO, this is the crux of the matter. Look at the pic below:

Assume the whole bar is well attached to the frame rails at each side (otherwise, it's definitely not good for a snatch recovery!). There is a huge difference between pulling on the receiver mount in the middle of the cross-bar, and pulling with a long harness attached to both ends. The direct receiver-mount pull will tend to bend the cross bar outwards, and pull the frame rails in towards each other (with a lot of leverage, on top of the many tons of force imparted by a snatch recovery).

 

[winkosmosis]

IMO, this is the crux of the matter. Look at the pic below:



Assume the whole bar is well attached to the frame rails at each side (otherwise, it's definitely not good for a snatch recovery!). There is a huge difference between pulling on the receiver mount in the middle of the cross-bar, and pulling with a long harness attached to both ends. The direct receiver-mount pull will tend to bend the cross bar outwards, and pull the frame rails in towards each other (with a lot of leverage, on top of the many tons of force imparted by a snatch recovery).

I don't visualize it that way. To me the crossbar seems rigid enough that the pulling force is straight back on the unibody, or whatever direction you're pulling

 

[DaveInDenver]

The hitch pin is 5/8" in diameter and so has an area of about 0.30 sq-inches. Grade 5 fasteners under 1" have a minimum proof of 85 ksi and grade 8 120 ksi. So a 5/8" grade 5 rod (or bolt with minor diameter of 0.625", so make sure to use a shouldered bolt long enough that the unthreaded part spans both receiver holes) will minimally tolerate about 25,500 lbf and grade 8 about 36,000 lbf without deformation.

Their yields are 92 ksi and 130 ksi, so a hitch pin would be 27,600 lbf and 39,000 lbf before leaving their elastic region. Where the difference in grade 5 and 8 comes in is that grade 5 has min tensile yield of 120 ksi and grade 8 150 ksi, so each could potentially fail at 40,000 lbf or 50,000 lbf respectively, so obviously there is a broader region where a grade 5 bolt would bend (from 92 to 120 ksi) compared to a grade 8 (from 130 to 150 ksi). But notice that the grade 5 bolt fails before the grade 8 even hits its elastic limit.

Also the bolt through a hitch receiver is in double shear, so unless you are driving a M35 and pulling out an M1A1 it's unlikely that you will stress a hitch pin or bolt to failure yanking out Hiluxes and Wranglers. The only disadvantage IMO to using the loop-and-pin method is convenience, stuffing the strap in can be a pain and sharp edges do need to be smoothed to keep abrasion minimized. But it's a perfectly legitimate and safe way to connect to a recovery point and does eliminate additional connections, which is good.

 

[I Leak Oil]

And with the hitch pin method you're usually limited to a 2" max strap as the larger size/capacity just doesn't fit in the receiver very well. I think it's just easier and better for the strap to use a receiver mounted D ring. I'm sure someone has seen one of these fail but I have yet to. If you can make one fail then the receiver hitch probably isn't the best point to be pulling from, still better than nothing though.