Request your help RE pin box movement

[Dayle1]

I'm starting a new thread, but here is a link to the original pin box movement. There is a lot of data here that would be difficult to duplicate, but everyone should find informative. However, at the end is a description of data that can be obtained on any Cruiser with a bedroom slide-out. I would really appreciate it if Cruiser owners with the old front cap would take this measurement and publish their data.



This week I took some more measurements to try and find where the flex was happening on my 32MK.Â* I set up three measurements, 1) absolute movement at the tip of the pin box.Â* Not having a forklift, I had to use the truck and since I couldn’t measure from the pin to the ground, I ran a reference bar above the pin box between several posts in my RV port.Â* Also, rather than use the fiver’s landing gear for hooking and unhooking, I used the truck’s air bags, although I didn’t quite have enough travel using just the air bags.Â* 2) I attached a laser level to the side of the pin box pointed at the front storage compartment.Â* 3) I used a micrometer to measure across the double rear crossmember, outside-to-outside dimension.Â* Measurement taken just beside the center floor joist across the bottom of the two crossmembers.



Additional details: distance from the storage compartment wall to the laser was 74 inches.Â* Total distance to the tip of the pin box was 88 inches.Â* Length of the floor structure is about 42 inches, leaving 46 inches for the pin box structure plus the extended pin box itself.



Results:Â* 1) Loaded, the pin box was 1-1/8 inches closer (higher) to the reference bar.Â* With the limited travel of my air bags, I’m guessing the real number is at least 1-1/4 inches and could be as high as 1-5/8 inches.Â* 2) Loaded, the laser spot moved DOWN 1/2 inch.Â* 3)Â* Crossmember distance measured 3.550 inches unloaded and 3.585 inches loaded, so the crossmembers seperated by 0.035 inch.



Calculations:Â* First , using 3), the crossmembers are 5 inches tall and a gap of 0.035 inch at the bottom is roughly an angular difference of 0.4 degrees between the first crossmember that is part of the floor structure and the second crossmember which is part of the pin box structure.Â* This slight tilt is responsible for the pin box moving up by 0.32 inch.Â* Using 1) (judged up to 1-1/4 inches) that leaves 0.93 inch due to flex in the bedroom floor frame between the vertical beam directly behind the storage compartment wall and the first crossmember.Â* This calculates to an angular tilt of 0.61 degrees.Â* Now, how does this compare to the measurement from 2)?Â*Â*Â*The combined angular tilt of 1.1 degrees predicts that the laser spot on the storge compartment wall should move down by 1.42 inches.Â* But at the same time the tip of the laser has physically moved up 0.789 inches due to the bedroom floor tilt and 0.22 inches due to the pin box tilt, or 1.009 inches.Â* So, this predicts that the laser spot should have moved down 0.41 inches vs. 0.5 inches actually measured and so I have confidence the data is reasonably correct.



Conclusions:Â* Pin box movementÂ* as measured to a stationary reference point (i.e not the front cap) is very comparable to whatÂ* CR and Lippert measured on Hank’s unit.Â* Based on the calculations, about 75% of the pin box movement is due to flex in the 42 inch bedroom floor structure and just 25% due to flex in the pin box structure.



Next, to verify my assumed flex in the bedroom floor structure:Â* The assumed 0.93 inch movement is out at the tip of the pin box.Â* But over the 42 inch width of the floor structure, that equates to a movement of just 0.444 inch.



Â* My next measurement can be done by anyone with a laser level and the trailer can be hooked and unhooked in the normal fashion.Â* I retracted the bedroom slide enough to lay the laser level on top of the carpeted frame rail at the rear (closest to back of the trailer).Â* This is the part of the upper frame rail that is attached to the lower I-beam by front and rear verticals and should not flex, so precise location of the laser level should not be critical.Â* Reverse hallway floorplans like my 32MK make this setup easier.Â* Anyway, I adjusted the laser to shine under the retracted bed and into the open wardrobe closet.Â* That way I could use the metal bottom track of the sliding door as a reference point.Â* Taking accurate readings was difficult, but I used the backside of the micrometer (used for depth measurements) and adjusted it until the beam hit the bottom of the micrometer body.Â* I measured a difference of 0.317 inches between hooked and unhooked.



While this is only about 75% of the expected number, the fact that I could clearly detect a noticable difference in the readings proves there is flex in the bedroom floor structure.Â* This is a measurement that can be done on any Cruiser with a bedroom slideout, old frame or new frame,



My request to Cruiser owners with the old frame. Is the flex in the bedroom in the same range of 0.3 to 0.4 inches? I really hope some of you will try this. Harbor Freight sells a 16" laser level real cheap.

[Dayle1]

Originally Posted by Dayle1

My request to Cruiser owners with the old frame. Is the flex in the bedroom in the same range of 0.3 to 0.4 inches? I really hope some of you will try this. Harbor Freight sells a 16" laser level real cheap.

Is there anyone on the forum willing to try making this measurement??? Send me a PM if you would like more assistance or call me at: 512-663-9507.This would be helpful to new Cruiser owners. Harbor Freight has a new level that will also measure angles for $25 and Amazon.com has a simple 16" laser level for like $13.

[fhenn]

I would Larry but not certain any thing I would get on mine would help

[Dayle1]

Originally Posted by fhenn

I would Larry but not certain any thing I would get on mine would helpÂ*

Frank,

Thanks, you are right since your Cruiser has been "modified" already, we need measurements from stock Cruisers.

[John B]

The only thing know for sure on our 2011 mk is static when I drop the weight on the truck the pin box mount where it bolts to the frame disappears 1/2 inch up into the covering. Going down the road I can watch it just continually pumping up & down like a jack handle the front cap is doing this in relation to the pinbox. But I have no way to measure it but you sure canwatch it doing it!! have a great day! Jb

[avvidclif]

I measured mine today. I have a level mounted on the front of the hitch. I measured from the top of it to the bottom of the front fiberglass. This is a point appx 3.5 inches behind the hitch pin itself so if the front fiberglass nose isn't moving then any difference would be in the frame/hitch flexing.



Unladen 2.75"

Laden 2.25"



That means the hitch is moving up .5" when the load is put on it. Not to bad in mt estimation.

[Dayle1]

Clif,



Thanks for taking the measurement, that 1/2 inch is pretty good, several of us have measured closer to 1 inch by a similiar technique. This is an ez measurement, but you did hit upon the one limitation, it assumes that the front cap is stationary. But that is not quite true. As Hank's photos show, there is a bolt securing the wall to the frame just a few inches behind the rear pin box crossmember, yet the frame will flex beginning at the front landing legs, so to some extent the walls, roof and front cap will not remain stationary.

[Dayle1]

Here is a way to measure flex in the bedroom floor structure that is very EZ to do. Took less than 20 min. including taking the pictures.



The first picture shows the target, a piece of 1/8 inch plywood propped against the front closet lip. The laser spot is clearly visible. This is actually behind the pin box structure, so any flex or twist in that portion of the frame is NOT being measured.





Second picture shows the laser position, tip of the laser is 45 inches from the plywood. This location puts the laser directly above the front storage compartment. This part of the upper frame should have zero flex since it is tied into the 8 inch I-beams in multiple locations and there is a 5 x 1-3/4 steel tube crossmember that is full trailer width directly under the laser tip.





The upper frame rails are 1-3/4 x 5 inch steel tubes, probably 1/4 inch thick steel and the floor joists are 2x2 inch steel tubes. So, what would be the expected flex in the bedroom floor over a span of less than 45 inches? Find out what it is on your trailer.

[Lloyd]

Larry, I finally got out there and checked mine this morning. I used the same setup as you.
I showed a difference of 1/8 in. Ignore the line in the middle.

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[Dayle1]

Lloyd, Thanks so much for getting this data, 1/8 inch sounds really good. For everyone else, Lloyd's Cruiser has the old frame layout and lacks a bedroom slideout.



By comparison here is my data from yesterday, I measured 9/16 inch difference as shown by this final picture.In my case, the difference is enough that I didn't need to zoom in.



This is movement that the walls and bed platform have to deal with every time the trailer is hooked or unhooked. Just one data point for each frame layout isn't very helpful. So, I hope more owners with both old and new front cap will duplicate these measurements.

[martinstwopopfarm]

Dayle,

I do not have the front bedroom slide. We have bunks up front, I have noticed about 3/8" movement in the front of the pin box and the cap.

[Lloyd]

I agree with Larry------It sure would be nice if some of you guys would do this same measurement he is asking for. It doesn't matter if you have a bedroom slide or not. I got my laser level from amazon for under $20. That isn't going to break the bank for anyone, and it's not rocket science to use the laser or perform this procedure. Larry has the steps laid out so they are simple enough even I was able to follow.
I use to measure from my pin box up to a point on the front cap to check for any flexing. I can see now that is "not" going to give a accurate measurement. Why??? Because the front cap moves right along with the pin box to a certain degree.

Come on guys jump in here and help.

[rcflyer]

I have a 2010 26RK Cruiser 5th wheel. I set up cribbing from my shop floor to the king pin. Jacked up the kingpin with a 12 ton bottle jack until the pressure was off of the landing gear. Made measurements to the nose of the pin box and to the backing assist mirror on the front of the trailer to the garage floor. I had a 1/4 inch difference. <?: prefix = o ns = "urn:schemas-microsoft-comfficeffice" />



I also tried the laser beam level. The trailer is a rear kitchen. I set the level in a cabinet aiming to the very front of the trailer in the bedroom. I used painters tape on the front wall and at the entrance from the main room and the bath area. Marked the tape before and after jacking. I saw no movement inside the trailer. This tells memy cruiser trailer frame is very stiff.



As a side note. When you jack the king pin to remove weight from the landing gear weight is transferred to the trailer axles. This will result in the rear of the trailer to go down as the springs compress to take up this extra weight. In my case the trailer hitch on the rear of the trailer dropped 9/16 of an inch. The trailer springs compressed about 7/32 of an inch. Thus some of the movement to raise thetrailer with the jack on the pin is a result of the springs being compressed. My 1/4 inch was the delta movement I measured from the pin box nose and the trailer front where the mirror is.



On the pin box I measured no movement with relation to the trailer on the rear attaching bolts and 1/8 of an inch on the front attaching bolts.

[cruzr4-2]

Larry, empty your mail box. private messages will not go through.
I have not been ignoring your request although it may appear that way. We've been busy with other things. Please be patient and I'll try to help out.
I hope I don't find something scary with my own.
Dennis

[Dayle1]

rcflyer,



Thank you for the effort you have taken on this. You are right there is some affect due to spring sag when comparing to an external reference point. But using your 7/32 inch drop at the springs and a distance of 172 inches from the equalizer to the landing gear vs. say 88 inches from the landing gear to the tip of the pin box, the error would be about 50% less or 7/64 of an inch. Not much compared to 1-1/4 to 1-1/2 inches observed by Crossroads on Hank's unit.



The test I posted yesterday has the laser level directly over the landing gear, so the affect of spring sag might be zero. But worst case error over 45 inches would be 7/128 of an inch, or just under 1/16 inch. Regardless, take the raw numbers or factor in a less than 1/16 possible error, there is still 7/16 inch difference between my measurement and Lloyd's.



More important, it sounds like you have very minimal flex in the gooseneck portion of your frame, both the pin box structure and the bedroom floor structure. So that is another data point.

[cruzr4-2]

Following are pics of measurements taken today of our 2006 29RE
The blue tape used is 1'' and the level was at the top of the steps at the bathroom and aimed at the front closet wall.



















For your enjoyment
Dennis

[Lloyd]

Unless I'm missing something here------(and I could be, so correct me if I'm wrong)
Neither one of you guys have placed your laser level in the right spot to get the measurement wanted/needed. It has to be placed "right" so you can measure the flex in the "bedroom floor area". Look closer at where Larry has his laser positioned in his picture.

[Dayle1]

Originally Posted by Old Farmer

Unless I'm missing something here------(and I could be, so correct me if I'm wrong)Neither one of you guys have placed your laser level in the right spot to get the measurement wanted/needed. It has to be placed "right" so you can measure the flex in the "bedroom floor area". Look closer at where Larry has his laser positioned in his picture.

Lloyd,

While it would help to have everyone make the same measurements for ez comparison, I think all the results so far are meaningful. Putting the laser further toward the rear of the trailer might increase the measured movement IF there was significant flex in the rest of the trailer frame. But there shouldn't be much.And if the numbers on the other units had been larger, like above 3/4 inch, then a new measurement might be needed. But so far the general data is that all Cruisers with the old square frame design have very little flex in any of the front structure from the the landing gear to the pin. So, thanks to everyone that has provided data on your unit.

[Lloyd]

I guess I need to apologize here, and I do extend one to all concerned. This is Larry's project not mine so I "should not" get so involved.Sorry guys.

[cruzr4-2]

Wow, a scolding on an RV Forum and more than one on a single thread.
Oh well