Dual Cam Setup

I had binding issues with my old dual cam setup. Sometimes the detent on the inside bar would not unlock from the cam on a turn. This put a lot of outward pressure on the outside lip of the cam. When this happened, sometimes the cam would lift up leaving slack in the chain because the cam was lodged into the detent. It would eventually let go and make a real loud bang. When this happened, the bolts that hold the cam to the frame would become loose or tear out. Sometimes on not so tight turns, when the detent of the bar was jammed onto the cam, I got bent snap bracket from the outward pulling of the chain, maybe 25-30 degrees off vertical alignment (on edit - maybe less of an angle than this). I did eventually get tired of trying to stop the problem and I switched to Equal-i-zer brand hitch. The commonality was that the bar did not unlock from the cam and it was related to binding. I could never get rid of the binding. No matter what I did, the instance of binding was just moved to another location. I think a lot may have to do with the slop between the hitch and the receiver of the truck. I also think the angle the bar makes on the cam plays a role. There is a lot to analyze. I also think the stiffer bars are less forgiving.

JBarca wrote:
The set screw drug the frame and headed towards the "bottom" of the frame. In order for the dig marks to go that direction the DC arm had to be lifted "up". Agree Yes/no?

I originally wrote that the chain was pulling up.... but went back and changed it.

When the WD bar is under tension, it's trying to pull the chain down. If the WD bar was centered exactly under the chain, there would be no twisting action. Since the WD bar is to the inside, there's a down force somewhere on the cam and the chain is resisting that force on the end of the cam. I think this creates a twisting action. This is why a small movement can be observed when the bars are snapped up (or when the tongue is let down - I'm not sure when it showed up).

JBarca wrote:

Now the frame crush at the DC frame plate. This pic aligns with the set screw rotation. The DC arm had to rotate "up" in order to crush the frame in. Both the set screw and the frame inward crush support an upward force doing this damage.

Yes, counterclockwise when facing the trailer from the coupler.

JBarca wrote:

If we determined the snap up area failed from the chain force pulling "down" on the snap up, and the DC area pulling "up" on the cam arm, then the 2 areas of failure happened at different times and from different force directions. Agree yes/no?

I was all ready to disagree, but I see your point. So I went back and changed my story some - to discuss this twisting action with the bar pulling down in one spot on the cam and the chain out at the end.

What if the spring bar is loading the cam at the inside keeper flange, basically as far away from the chain as possible. Also assume that since it's all new and not worn in, that the bar is only contacting the cam on a small portion of the bar - at that flange. I'm stacking the deck here to see if my idea is even remotely possible. So, the bar is pressing down on one side of the cam, and the chain is resisting that force on the opposite side of the cam. This would produce a twisting force, but I don't know how much.

I don't have the bar here, or else I would get a photo to see where it's starting to wear....

JBarca wrote:

This is why I think there are 2 separate events that caused the failures. The force directions to cause the failures are in opposite directions.

I'm trying to picture the load changing direction on the chain at the cam mount. Can it? In order for there to be any damaging forces at all there needs to be tension on the chain. Won't this tension always be from the same source - spring bars trying to pull down and chain/snap-up resisting?

JBarca wrote:

Keeping an open mind to this, after all this review is there anything else on that very short trip you made that sticks out to cause forces in the directions we are talking about? A hard bump from a pot hole etc?

I can think of two compound angle turns

One was a left out (and then back in later) the driveway.

The other was a compound angle right turn, leaving my neighborhood out onto the main street. I'm pretty sure we've done that turn a few times as well. It's not a hard angle, but the trailer is higher. If I had to pick a turn/event candidate that would be it.

When coming back we did not do the reverse (left turn) into that compound angle turn.

Campin LI wrote:
I have been following your thread. I have a question - Has anyone ever reported having a bent snap bracket when not using dual cam with Reese WDH? I am not on the forum that often but I have never read about one. Based on that, I would lean toward dual cam having something to do with bent snap bracket.

That is a good question. It might be a stretch that no one ever had a snap up failure on a non DC hitch, however we do hear about the Reese DC ones more.

Anyone ever had a snap up failure that was not a DC system?

Read my posts above, we may be onto something unique to the DC aggravating the problem.

mrekim wrote:

JBarca wrote:

On the non DC hitch the chain attached to the WD bar will swing towards the TT. Since it is attached to the WD bar, it is harder to see that inside WD bar unloading. And it may take more angle difference between TV and TT to go to zero load, however the load is still significantly reduced because the hitch head is titled in a force unloading direction.

This one I'm having a problem seeing. I always figured that, since the chain restricts movement, the inside bar won't unload much. If I'm picturing this correctly, as you turn, the outside bar chain will get pulled forward some and the inside one will get pushed backwards. Since the chain restricts movement and will effectively pull the spring bar up as it's pulled either forward or backward it seems like there will always be a non-trivial load on both bars.

I admit, I'm not picturing the compound angle hitch head movement you're describing yet. Would you expect both bars have a non-trivial amount of tension on a turn on flat ground?

A realization is "maybe" forming. The DC may add a load to the WD bar above the standard chain swing in the compound angle turn combined with a back flex situation to create a very high load in the snap up.

At this point I need to prove it or dissprove it to myself. I have studied/used the DC for so long it did not dawn on me until your post here thinking through this, the DC effect may be larger than prior thought. And you couple that with a very thin and flexible A frame rail and the combo may not be good.

While this may add to the reasons of why more DC's have shown up with up snap up failures, it does not answer why your DC frame plate crushed inward. Your A frame is part of something in the middle of all this. I cannot connect the dots where the DC caused "all" of the issues. At least not yet anyway. If someone was going to break a A Frame with a DC, 1,700# setup should of broke it by now.

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.

mrekim wrote:

JBarca wrote:

It is a fact that making a turn with a conventional WD hitch where the truck and trailer wheels are on different surface angles changes the hitch head tilt in relation to the trailer A frame. If the trailer wheels are on level ground and the truck on a surface that on angle (say 5 or 10 degrees for example) in relation to the TT, the hitch shank in the back of the truck is going to follow the truck and the hitch head with the tow ball in the coupler will pivot the WD bars. The hitch head movement will change the loading on the inside and outside turn WD bar. How much it will change will depend on the angle and the head tilt of the hitch.

Let's see if I have this right. If the truck and trailer are in line and the truck is pointing down the it will reduce the tension on the WD bars and if it's pointing up it it will add to it. Does that seem right?

I'm not picturing how tuning changes things from side to side though.

Yes, you are correct, if the truck front tires are heading down hill and the back of the truck and the TT are still on flat inline ground, the WD bars will unload for a moment in time.

And if the front truck tires are going up hill and the rear tires and TT tires are on flat inline ground, the WD bars load up more from the flex in the hitch. We nick name this "back flex" in the hitch. The bars load up, lift the TT and TV rear until they come to equilibrium. Nick name that "truck lift". Since the truck is rolling, this all happens very fast but the WD forces all changed very quick too.

The turn:

If the TV and TT are on the same hard surface inline (same plane) road and a turn begins, the loads in the WD bars are closer to equal through the turn. That is as long as you do not have extreme hitch head tilt angle. There is some WD bar load change from the trunnion lug angles.

Now throw in the truck rear tires being on an road surface which is on an angle to the TT wheels. And turn the truck at the same time. I'll call this a compound angle turn. The hitch head stuck in the truck receiver is going to rotate with the truck. The hitch head is held to the TT by the tow ball. In this process the head rotates on the ball in relation to the A frame and can change the angle of rear tilt on the WD bars.

See here. This is a mock up to show the point. The outside turn side of the hitch head goes down hill adds more head tilt to the WD bar increasing the load. The inside turn side of the head goes up hill removing head tilt which the WD bar decreases the load on the WD bar. In the case the truck is also heading down hill in relation to the camper

Now lets follow it on the truck and camper hitched up. A view from the front in a 50 deg turn on unlevel ground and not by much.


A top view


And the side view. The hitch head ball platform on top is tilted 5 to 8 degree in relation to the TT A frame. That is enough with the angle of the trunnion lugs in the head to unload the inside turn WD bar and the outside WD bar holds all the load plus ride up the cam.


I may of added some confusion about inside turn and outside turn before but is all depends if the truck is going up hill in the turn or down hill in the turn if it is the inside or outside WD bar that unloads. Truck going up and right is different than truck going down and right and so on.

I'll leave you with this for now. Be back tomorrow. Got to go the sleep... You were typing as I was before...

Thanks

John

I have been following your thread. I have a question - Has anyone ever reported having a bent snap bracket when not using dual cam with Reese WDH? I am not on the forum that often but I have never read about one. Based on that, I would lean toward dual cam having something to do with bent snap bracket.

Hi Gerry,

Good pics! Really nice and learned something new as the older snap up I have seen but not in that detail and in the light of the conversion we are now having. Thanks for sharing.

TUCQUALA wrote:







So my thoughts are: How much more or less twisting force is applied to the trailer frame under normal towing events, which would include turns, driveways, twists and turns, by each of these snap ups??? Which would be better for these new, weaker trailer frames???

I think the older style would be less prone to have a failure. I know I have had one fail with the new hitch, but I still believe there was something abnormal happening during the first setup. The snaps and bangs were way out of line.

Gerry

The older snap up for sure has a chain pull closer to the frame at the top. The older style DC, the one with the U bolts, has the chain closer to the frame at the bottom. It "might" have been Reese's intent with that older standard DC to be as straight up and down as possible so the snap up hook was closer to the frame. I'm speculating this, not knowing it for fact, but it would make sense the designer made it that way.

Then came along the new HP DC and around that time the newer snap up. The HP DC no longer has a saddle clamp for the chain, it has a chain plate hanging from a canterlivered DC arm. So this snap up shifted the hook out a little more in attempts to not pull on the cam arm at an angle. Again speculation but maybe the reason

Here is the older standard DC but the new snap up. This was a 2004 TT


See the chain in the middle of the WD bar at the bottom


And then the new HP DC off to one side and out furhter.


As far as side forces, using the older snap up on the newer HP DC can put a larger angle to the chain from the hanging point as it is closer to the frame. However using the newer snap up may make the chain straighter but it then creates a canterliver on the snap up. In both cases the force on the frame is a twisting force.

On the older standard DC and the older snap up that may have been a lower twisting force on the A frame then the new HP DC

And I believe the older snap up on the newer HP DC may be slightly lower twisting than the new snap up, however maybe not a lot. The problem is end attaching point to the cam arm is still a good distance from the A frame creating a force pulling on an angle creating twist in the frame.

I like the trueness of the older snap up however I like the retainer clip of the newer one better.

Thanks again for sharing the pics, it helps add to this post of snap up failures

John

JBarca wrote:

It is a fact that making a turn with a conventional WD hitch where the truck and trailer wheels are on different surface angles changes the hitch head tilt in relation to the trailer A frame. If the trailer wheels are on level ground and the truck on a surface that on angle (say 5 or 10 degrees for example) in relation to the TT, the hitch shank in the back of the truck is going to follow the truck and the hitch head with the tow ball in the coupler will pivot the WD bars. The hitch head movement will change the loading on the inside and outside turn WD bar. How much it will change will depend on the angle and the head tilt of the hitch.

Let's see if I have this right. If the truck and trailer are in line and the truck is pointing down the it will reduce the tension on the WD bars and if it's pointing up it it will add to it. Does that seem right?

I'm not picturing how tuning changes things from side to side though.

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.

JBarca wrote:

On the non DC hitch the chain attached to the WD bar will swing towards the TT. Since it is attached to the WD bar, it is harder to see that inside WD bar unloading. And it may take more angle difference between TV and TT to go to zero load, however the load is still significantly reduced because the hitch head is titled in a force unloading direction.

This one I'm having a problem seeing. I always figured that, since the chain restricts movement, the inside bar won't unload much. If I'm picturing this correctly, as you turn, the outside bar chain will get pulled forward some and the inside one will get pushed backwards. Since the chain restricts movement and will effectively pull the spring bar up as it's pulled either forward or backward it seems like there will always be a non-trivial load on both bars.

I admit, I'm not picturing the compound angle hitch head movement you're describing yet. Would you expect both bars have a non-trivial amount of tension on a turn on flat ground?

Hi mrekim,

I may have not used the right words about the snap ups per your response. But, I think we are on the same page, just want to clarify some points.

mrekim wrote:

JBarca wrote:

I have not yet figured out if the DC addition to the WD hitch created all this frame issue. Not that anyone is yet pointing to the DC to aggravate this frame bend at the snap up issue, just I myself have not connected those dots yet.

I believe the DC contributes to the forces attempting bend in the face of the frame.

Lets clarify. There are 2 areas a frame failure and I'm thinking they are coming from 2 different force directions and 2 different events. Here are the 2 areas.

1. The snap up area
2. The DC mounting area

What I was wondering on was, are they independent or do both need to be combined to occur? Or said another way, Is the failure of the frame at the snap up "caused" by using a DC?

I cannot "yet" connect the dots that the DC was the cause of the snap up area failure or added to aggravating it. It "appears" the A frame snap up area failure was caused by the loads imposed by the WD pulling "down" on the chain in a compound angle turn and the frame could not handle them. This "could" of happened without a DC installed. And any of the brands of snap ups I listed "may" have produced the same effect. This will be a key point with Coachmen.

The evidence for sure points to the snap up area was caused by a "downward" force pulling on the chain. Agree, Yes/no?

mrekim wrote:

We agree there's considerable force at the bottom of the snap up. And I think we agree that it gets worse if anything goes south (snap up bends, frame bends, etc.)

Yes, we 100% agree. Yup, you got it.

Now lets go to the 2nd area, the DC frame mount. This area has something else going on. This is why I'm saying the 2 failures have different attributes to them.

mrekim wrote:
In addition, I think there's a rotational force on the dual cam mount where it wants to rotate into the face of the frame. Those self tapping screws in thin sheet metal aren't much of a deterrent.

I'm pretty sure the dual cam frame bracket rotates a little as soon as a load it applied, so some rotational force is always there, it's just a matter of how much.

Here is the set screw pic. It dawned on me from you showing this again. The set screw drug the frame and headed towards the "bottom" of the frame. In order for the dig marks to go that direction the DC arm had to be lifted "up". Agree Yes/no?


Now the frame crush at the DC frame plate. This pic aligns with the set screw rotation. The DC arm had to rotate "up" in order to crush the frame in. Both the set screw and the frame inward crush support an upward force doing this damage.


If we determined the snap up area failed from the chain force pulling "down" on the snap up, and the DC area pulling "up" on the cam arm, then the 2 areas of failure happened at different times and from different force directions. Agree yes/no?

The heavy downward chain force that collapsed the snap up area would of pulled out on the DC frame plate screws trying to rip them out of the frame, not collapse them inward.

mrekim wrote:

If my analysis is correct, then the dual cam design is "doubling down" on trying to bend the frame vs just using weight distribution with snap up bars.

Help me understand what your saying here. Double down that is.

I "believe" the DC frame area failure came from fact of the high tongue weight and a 1,200#WD bar just going straight ahead totally independent of the snap up. The turn did not kill this one.

Let me try and explain as your other comments help support this. Truck is straight ahead, both WD bars are fairly equally loaded. At this point the snap up area may be fine and resisting the chain force pulling on it as both snap ups are taking close to equal load.

Down at the DC area the chain is pulling "up" on the cam arm from the normal WD forces. This WD up force on the DC arm bent the DC frame plate into the A frame and in the process rotated the DC frame plate scraping the pinch bolt towards the bottom of the frame.

You said yourself you noticed cam arm flexing on the frame from just letting the TW down on the bars. It may have been one bump just plan going straight ahead or in a slight turn to laod one WD bar more and the bounce impact shock bent the DC area inward by pulling "up" on the chain.

This is why I think there are 2 separate events that caused the failures. The force directions to cause the failures are in opposite directions.

Bottom line, your A frame can't handle the side imposed forces of this hitch in the current configuration. The DC is unique to Reese, however the snap ups forces are common to many other brands that use a chain.

There is something for sure different about your setup. There are lot of folks with an Excursion, heavy TW campers, WD hitch with chains and even tube A frames. An unknown is the tube strength on theirs and yours. Why would yours be so much different?? That is a good question not yet understood. I knew when I saw this failed from your pics the 1st time, WOW that's a new one. Many folks have ripped out the threads of the DC frame plate from a bind in the hitch. Yours is the 1st one I recall seeing bent in. Maybe someone else can bring up another inward failure.

Keeping an open mind to this, after all this review is there anything else on that very short trip you made that sticks out to cause forces in the directions we are talking about? A hard bump from a pot hole etc?

Hope this helps

John

PS we have had other campers with Tube A frame failures, I tried to remember the guy who's entire A frame broke off at the header. I hunted for it and can't find. His camper mfg replaced the whole thing in his drive way. Pics and all of it. Was a few years ago. And then there are folks with channel iron A frames too small for the loads and they buckle the headers too. Both steel shapes can be made to work providing they are strong enough for the TW's and WD hitches needed for that TW.