Dual Cam Setup

mrekim wrote:

JBarca wrote:

On the DC, since the chain does not swing like a non DC WD hitch it is easier to spot that the inside turn WD bar can totally unload in spring force. And it does not take very much angle between the truck and trailer. I have seen it and measured it in my own driveway.

I don't think the truck and trailer need to be on different planes for this to happen. I think all that is needed is for the inside bar to make it a certain distance back in the turn. Basically, once it completely pops out of the curved portion of the bar it frees up.

Here's a photo. I think that once the outside bar gets past that arrow that the inside bar will be completely unloaded.



The outside bar rides up the bend in the end of the bar. I assume this has the same impact as adding tension to the chain. Maybe this action is another piece of the puzzle. The inside bar pops loose and may be "free" as soon as it's popped completely out of the bend. As you turn the outside bar gains tension quickly while the inside bar looses tension due to the bar angle.

What you are saying is correct, when one WD bar is totally off the cam that bar has less load and can be at 0. In addition, the bar on the other side can be very high up the cam and increasing load. This is very true. However, there is a larger load when the truck surface plane is on an angle to the TT. It magnifies the problem. You have both the increased WD bar tension from riding up the cam and you tilted the hitch head in a direction to even further increase the WD bar tension.

This pic shows both added together. The outside WD bar is very far up the cam. This can be close to 1 chain link more of tension. Then look at the hitch head and the trunnion lug angle, the tilt back towards the TT is even more then it is when the truck is going straight ahead. Changing the angle of the hitch head in relation to the TT can add more tension like tilting the head back a few more teeth.


While this turn in the pic above was about as far as you are going to go before other issues arise (74 deg turn), the TV/TT plane angle of the back of TV to the TT was not as large as it can be. Also, add in the effect in some cases there is back flex added on top of this in a turn.

When the combo of a larger degrees of turn, more surface plane angle between the TV rear wheels and TT wheels and the event of the truck going up hill relation to the TT (back flex), those 3 events can create a very large chain load pulling down on only 1 side of the A frame. These events happen on a WD hitch all the time. There is one difference though between the DC setup and the standard WD system less a DC, it is the DC effect we described above. It is very possible by the WD bar ridding up the cam which increases WD tension is much higher then when a chain swing of a chain attached direct to the WD bar given the same set of surface plane and truck up hill (back flex) conditons.

I have seen A frames twist the frame rail to the point it buckled the header from this very fast, very large load on only one side the A Frame if the frame rails are not made strong enough to handle the twisting loads of WD. And those where non DC systems.

Now that I think through this explaining it, the DC added load effect might be very high as opposed to the chain swing effect of a non DC hitch. If this is correct, then the DC system can have more chain pull load in a compound angle turn then the standard WD hitch. And if this is correct, then the snap up loads may be higher with a DC system.

I happen to have both, the Reese trunnion bar DC hitch, for the camper and the non DC Reese trunnion bar hitch for my equipment flat deck trailer. This curiosity may drive me to an experiment this weekend to show the differences between the DC and the standard chain swing effect. I’ll see if I have some time to go set it up. The more I think about it, this could be the difference in the what “might” appears to be a higher rate of snap up failures on the DC system.