Dual Cam Setup

mrekim wrote:
I made a video of the snap up and the spring bar on one side. It's pretty boring, but it does show that's there's some motion in the snap up. It was surprising to me how often the little keeper pin is holding some amount of weight. I assume that when "popped out" the keeper is bearing a non-trivial (or certainly non-zero!) load.

http://www.youtube.com/watch?v=hg8XwpmSy_w

I'm not sure if this help at all with the Dual Cam issue. I guess it does if whatever force is causing the arm to want to go "out" still exists with the Dual Cam setup.

Actually it does help, or at least helps me realize a few things to add to this topic. I did some digging into your setup with no DC installed.

Lets look at your video pics with no DC, but a level of WD.

Here is where the toggle is locked in towards the camper


And here is when it is popped out


When I first saw that pop out, with your TW of 1,100# it did not add up with the heavy load of WD as to how the WD bar could undo the toggle just making a turn. The WD bar pivots in the hitch head, The chain is under heavy force, well normally it is, there should not be that much side thrust. So I started doing some investigating.

My belief is when you are running 9 links and did not adjust the hitch head angle from where you were with the DC, you have reduced the WD force load by a fair amount. With that much reduced chain force, the bar swing will undo the toggle.

I went to my DC chain plate and chain to do some measurements. I wanted to back into what is the chain WD force with the chain plate using 6 links under load and then what is chain WD force with the chain U bolted to the WD bar and no DC? That is a good question.

Since I have a "collection" of Reese hitch parts (I'm a good customer) I realized a few things. Your hitch only has 9 chain links, h'mm, my original one has 11 links and looks thicker chain. Measuring the old and new hitch parts, here is what I found.

My 2003 bought HP DC chain has 11 links, a cross sectional link thickness of 0.330" dia. and a chain link pitch of 1.355". (On my current camper)

My 2007 bought HP DC chain has 9 links, a cross sectional link thickness of 0.300" and a chain link pitch of 1.380" (now on my flat deck equipment trailer) This one appears to match what you have.

It appears Reese changed the chain over the years somewhere between year 2003 and 2007. Have no idea why. Cost reduction??? See here:

My 2003 DC chain. 11 links as I run on 7 links under tension


My 2007 bought HP DC chain with 9 links. I bought this in late 2007 when we bought the current camper. When I sold my prior camper I put a new DC on it for the new owner as I kept my original DC for my current camper. On this smaller low riding camper I ran 5 links under tension as the I only had 6" of DC ground clearance.




And now your 2013 DC setup


I still have the 2007 chains from the DC kit. The new owner of my old camper had a Reese HP hitch, just no DC so I put his chains on that new DC. I use the 2007 chains now on my flat deck trailer along with my older 1,200# WD bars as a stand alone WD hitch. Basically your setup when you went for a ride in that video.




I want to stab at determining the WD force on your rig with the DC on 6 chain links and then running 9 links and no DC. When you took off your DC and put the chains on the WD bars, I "assuming" you did not change the hitch head angle. Please confirm, yes/no?

Measuring my DC chain plate and 2" diameter DC lobe, the 2007 vintage DC chain like yours, I come up with 3.84" in the length the DC chain plate needs to connect to the cam arm verses hooking the chain to the U bolt on the ends of the WD bar.

When you removed the chain plate and went from 6 links to 9 links under tension you reduced the WD by a fair amount. 3 chain links with a pitch of 1.380" is 4.140". Subtracting the DC chain plate of 3.84", you are 0.30" longer on chain under load. OR 0.300" less preload on the WD bar. This is were the less WD came from.

(Edited 11-25-13 to correct chain plate to 3.84 in place of 3)

Be back later after I get some more WD bar displacement distances when the hitch goes through a turn with and without the DC installed. We can then start putting estimates on the chain forces.

John

I made a pair of these today:






Dealing with the radius on the frame mount was a bit of a pain:




This is supposed to be an implementation of this "no drill" solution to beefing up the install:


The studs are 1/2" grade 5 bolts with the head cut off. One side is 1/2-13 and then when I did the 2nd one I decided to do 1/2-20. The studs for the snap up will be 1/2-20 as well. I may try to get away with just the top stud for the snap ups.

Yes, I think that all makes sense.

Hi Mrekim,

Sorry this took forever... work travel and "life" has been in the way however that has not stopped the "thinking" about your frame issues. Most of it was on an airplane flying to and from home with nothing to do but think... I have some time in the next few days so here is a start.

First you gave us a lot of detail to work with. :C

From the description of your journey on the day the frame bent, and the one video link, here is the location that "might" of been the blow that bent the frame. Granted this has speculation to it, so take it as a, well is "might" be rather than this is what did it. If you really want to confirm this, it can be done scientifically however the cost is not practical in your case. It is as "simple" (yeh right...) as mounting strain gages on the A frame and putting a load cell in the chain, load up the camper and go for a drive. Unless you have a buddy who does this for a living that can do it for free, trust me, you can replace the entire A frame 2 to 4 times for the cost of that work. I buy it often for work and it is the method when all the high end FEA programs cannot figure out what is going on. The failure analysis software is only as good as the force inputs and the where they are all coming from. Miss a few forces and the end result is not right.

This will take a few posts but here goes. Here is a progression of your journey from your video link. Please confrim we have this right as we need to review where the damaging blow occurred to then back into what might have caused this.

Here is the truck heading down the hill


Here is an approximation of the angle of the truck. You are heading down hill approx 4.5 to 5 degrees


Continuing to the intersection. This turn will create what I refer to as a compound angle turn with a level of back flex in the WD hitch. A double wammy for high forces in a WD hitch and the A frame. These forces happen all the time when using a WD hitch. The question comes to, does the DC magnify it? And then can the present construction of the camper A frame, take it?


The back flex action is starting now as the camper is uphill and the EX is on the level. As the TV turn progresses that turning action starts rotating the hitch head in relation to the TT A frame.


Now to what "might" have created the combination of back flex and compound angle turn at the same time. Notice the truck rear axle drops fast into the edge of the road where the road crown drops off. And the driver side tire goes down, yet the passenger side tire is up. Now throw in, if this was a somewhat quick motion of the turn, the back of the truck would bounce creating a very high dynamic impact load down into the hitch head and raising the driver side WD bar force very high for a moment. Going real slow, the trailer will just lift from the increased WD force and find it's own natural resting spot. This impact load by the rear of the truck bouncing is a total wild card right now. When it happens real fast, the load goes up instantly and that peak load "might" have been the damaging blow that bent the snapup and collapsed the frame behind the pinch bolt. The DC arm then may have twisted along with a high break away friction load traveling up the cam arm into the first bolt of the frame bracket that you had a washer behind. That washer in this case may have aggravated a point load into the side of the A frame with the thinness of the frame.


A close up


And some lines drawn on your TV and in relation to the TT axle road plane.


There are 3 axis's of rotation going on all at once. The TV frame (front to back across the WB), the left to right on the TV rear axle, and then the TT axles are on the road uphill to the main road the truck is on. When those 3 angles get like what you have shown us, the forces on the drivers side of the TT A frame go way up and the passenger side of the A frame go way down. The difference between having a DC or not is mixed in the middle of all this along with that dynamic bounce possibility of the back of the truck.

Now back to the 3 pics from page 10. The mock up of the back flex in the hitch. Don't have the compound angle turn in there as I did not have pics to help show this


And where the forces may be acting on the A frame.


And the result of the damage along with which way it is pulled out or pushed in.


This pic of yours (just turning the wrong way) does show how the hitch head rotates on an angle in relation to the A frame which will load up one WD bar more and relive pressure on the other in a compound angle turn


And here is the bend from the snap up




OK before I start down a tangent of how big the forces "might" be, please confirm the assumptions I presented are right to start with.

Be back later tonight. Have to go to the lumber yard and buy more "work".

John

Maybe you could research what type WDH other people who have your identical trailer are using...... and if they are having any problems.

Campin LI wrote:
I think the repair is the easier part.

I tried to contact 5 or 6 different welding/fab shops to get it fixed. Only two were willing to call me back. Each had a very different approach to repairing it with one being 5x the cost of the other.

It's at the dealer now, we'll see what they propose for a fix and at what cost.



I don't have any way to evaluate if the existing frame is compromised and if my proposed "bolt on" repair or those proposed by the two shops I contacted are sufficient.

Campin LI wrote:
Finding the cause is the hard part. Enough force was added to your frame to bend it. If you make that stronger, the next weekest part will bend/break. My guess is that your cam arms will bend. On mine the frame did not bend, only the bolts tore out. Over time, the cam arm did bend, so after your repair, I'd keep an eye on that.

I understand the next weakest point issue. But the $64,000 question for me is still related to what load the center of the tube frame can reasonably take and how did the force that bent it get applied. JBarca provided one possible answer to how it got applied a couple of pages back.

I'm still working on the assumption that thinner frames combined with heavier tongue weights are not compatible and there's not enough safety built into the design to protect the frame. If I'm right, then the frame is way weaker than the next weakest part and nothing else should break.

If I start bending cam arms, or any other part of the system once the frame is strengthened then I'm going to have to declare the above assumption wrong and figure out what to do next.

I think the repair is the easier part. Finding the cause is the hard part. Enough force was added to your frame to bend it. If you make that stronger, the next weekest part will bend/break. My guess is that your cam arms will bend. On mine the frame did not bend, only the bolts tore out. Over time, the cam arm did bend, so after your repair, I'd keep an eye on that.

I'm still around. I'm trying to get Reese to work with Lippert to determine what happened, if the frame/dual cam are even compatible and what the best fix is. I don't think it's going to be a quick process.

I'm also trying to come up with my own independent fix. Here's what I'm currently thinking:

OMG, the mod is getting nervous!!!!

After 11 pages and 105 replies, perhaps everything that needed to be said already has been. :W
Barney