Safety chains - choices, choices, choices

Originally Posted by PopBeavers

The coiled cables are self tightening. With chains I would have to use bungee cords to stop them from dragging on the pavement.

There are only two criteria, it seems to me, that must be met:

1. add the proper legal and feel good safety margin

2. are easy and convenient to use.

Safety chains should never drag on the pavement, except in those rare instances when you are going up/down a driveway where they will momentarily touch the ground. The slack in the chains should be adjusted so they ride well above the pavement and yet allow the vehicle to turn the tightest turn possible without "straining" the chain. See the hook up diagram below.

I use a "link" to attach my chains rather than the "S" hook. I loop the chain through the holes in the hitch plate and then attach the removeable link to one of the loops in the chain for a positive connection without the possibility of them coming loose through jarring. I began this type of connection with our Coleman tent trailer back in the 1980's when I lost the trailer because I had not seated the trailer hitch correctly to the hitch ball. The first bump I went over while leaving the campground caused the hitch to jump off the ball. Forturnately, I had used the crossed chain hook up, so the tongue remained off the ground and I was able to bring the car to a safe stop and reconnect everything properly.

I've since used the hookup described above with every trailer we've owned and have never had a repeat of the disconnect.

[ShrimpBurrito]

Thanks for the heads up on not using grade 8 bolts. I'll definitely just replace them with a grade 5. Incidentally, I was looking at a 26-foot 6,000 lb conventional travel trailer at someone else's house the other day, and the safety chain for it was fastened in a similar way -- one 3/8" bolt. Yikes. Just doesn't seem like enough.

It would seem prudent to at least attach the 2 halves of the chain separately with 2 bolts to split the load, although I'm guessing both chains would not be pulled taut in a run-away situation.

Dave

Chains on our 2002 2720SD were great; slinky cables on our 2008 3326 are even better. Just my opinion.

[ShrimpBurrito]

Freedom -

I just read this article about grade 5 and 8 fasteners, and it seems to indicate that although grade 8 fasteners are indeed more brittle than grade 5, it's only relative and not a difference in brittleness that would ever be experienced in a towing capacity. If you end of reading the article, do you think that what he is saying correct?

http://www.rockcrawler.com/techrepor...ners/index.asp

In the article, the author states:

"I’ve also heard the argument that grade 8’s are more brittle than grade 5’s and that’s why you shouldn’t use them. Well, first you need to understand what the term “brittle” really means. Brittleness in bolts is defined as failure at stresses apparently below the strength of the bolt material with little or no evidence of plastic deformation. Typically, fasteners are not brittle below 180 ksi ultimate tensile strength. Grade 5’s have an ultimate tensile strength of 120 ksi and a grade 8 fastener has an ultimate tensile strength of 150 ksi. This is why brittle is a relative term. Nearly all fasteners are considered ductile except some made from PH 15-6 Mo, 17-4 PH and 17-7 PH."

Using the calculation and reference in the article, the grade 5 3/8" bolt that is used to fasten the safety chain to the tongue (and also the tongue jack) has a sheer strength of 8295 lbs. That is enough to pull the trailer straight up off the ground, so it would seem that one such bolt would be plenty to secure the safety chain.

Using that same calculation, a 3/8 grade 8 bolt would have a sheer strength of 10,064 lbs.

Dave

[Bill]

Originally Posted by ShrimpBurrito

Using the calculation and reference in the article, the grade 5 3/8" bolt that is used to fasten the safety chain to the tongue (and also the tongue jack) has a sheer strength of 8295 lbs. That is enough to pull the trailer straight up off the ground, so it would seem that one such bolt would be plenty to secure the safety chain.

Shock load ("snapping" the chain) as opposed to staic load (the weight of the TM) will play a big factor here. If I snap the chain fast enough (as might happen in a disconnect accident), I can generate enormous shock loads, far in excess of the weight of the TM.

Bill

When I worked on snowplows in the Air Force, we would have to change the "cutter blade" on the bottom of the plow. When we used grade 8 bolts, they would shatter, with grade 5 if you hit something they would stretch a little instead of breaking. You still had to replace them, but the cutter blade would still be there, where with the grade 8 it could come off. I would trust grade 5 more under the conditions of the chain snapping tight and the bolt stretching, over grade 8 where the head snaps off and you're left with the chain dangling from your TV while the trailer goes down the road. YMMV

[ShrimpBurrito]

Thanks for the input. So while a grade 8 bolt may be best in an ideal environment, it sounds like what you experienced with the plow was in line with what was posted here earlier about grade 8 strength being quickly weakened by degradation. Ok, I'm sticking with grade 5.

Incidentally, I checked the safety chains on a 6,000 lb 27 foot conventional travel trailer recently, and its chains were only attached with one bolt...didn't look any bigger than 3/8". Not sure if that inspires confidence or scares the crap out of me knowing they are all over the road.

Dave

Don't get me wrong, grade 8 bolts are ideal in certain circumstances where there is a need for extreme clamping forces. (head blots on an engine) Where, IMHO, grade 8 bolts are not the best choice is where there will be a shock load. The cutter blades on snow plows are hardened steel and when they hit something there is a lot of shock. Grade 8 bolts don't take that shock very well - in many cases they snap - usually the head. I think the safety chain on a trailer is that type of application because if it's ever needed, the chain will come under a sudden shock load which may break the head off a grade 8 but not a grade 5. This again is my opinion from observations in the truck industry for 40 years. I have no "scientific" backing for these observations. I would just feel safer with a grade 5 bolt holding my safety chains than with a grade 8. I am going to change my tongue jack to an electric and when I do I plan to change the chains to 2 separate chains with two separate bolts. I will go to a larger chain, also. I plan on using at least a 5/16 welded chain (high tensile strength) - probably the type they use for aircraft loads which are 15,000 lb chains.

This is an interesting discussion. The next time I see my son I will ask him what he knows.

For what DW and I paid to send him to CalPoly for 5 years to become a mechanical engineer, the least h can do is enlighten me on the difference between grade5 versus 8 bolts and their application.

These days, he designs satellites. Not exactly the same as a trailer chain or a snow plow blade.

[ShrimpBurrito]

In gazing at the tongue today, I came up with what I think is a MUCH better way in attaching the safety chain.

The tongue is just 2 pieces of steel channel that make a "Y". The channel of course is hollow. I'm thinking about drilling a hole dead-center through the side of the channel, all the way from the outside of the tongue to the inside of the tongue (thus, actually drilling 2 holes). Then use the biggest bolt that will fit through a chain link, and slip it in the first hole so that you see the bolt while looking down through the channel. Slip the chain inside the channel, and then feed the bolt through the second hole. Put a washer and a nylock nut on the bolt, and just snug it up lightly, as you don't want to collapse the channel. Do this to both pieces of channel that make up the tongue.

This way, the chain is anchored at TWO spots, AND each spot would require the bolt to actually break in half in order to fail.

Thoughts? Comments? I've attached a crude drawing.

Dave