Pinbox Deflection-How much is too much? - Montana Owners Club

prndl · 01-02-2018, 10:06 AM

I have noticed that when I'm hooked up that my pinbox is slightly tilted upward.

I went out and while the trailer was in the driveway I put a post under the front of the pin plate and used my floor jack to lift the pinbox to see how much deflection it really is. It moves up about 3/4 of an inch when the landing gear is just off the ground.

Is this too much flexing in the frame? Is this an indication of "frame flex" or just normal flexing of the unit?

I'm considering getting a Reese airborne sidewinder pinbox and was concerned about the angle of the rear swivel post not being exactly vertical due to the flexing.

I know not many of us have actually measured the flex of our pinboxes but maybe some have noticed if their pinbox is tilted upwards while hitched and what is normal and what is a problem.

CaptnJohn · 01-02-2018, 10:14 AM

You are the 1st I know that actually measured it. When hitching I can see my pin box move slightly. 3/4" maybe??

cw3jason · 01-02-2018, 10:30 AM

https://www.lci1.com/assets/content/...sheet/0236.pdf

This is how you measure, then call Lippert with your number. I believe 1/2 was the allowed amount.

prndl · 01-02-2018, 10:43 AM

Thanks Jason, but that is for frame flex in the area measured. My concern is the mount for the pinbox twisting upward. That area is forward of the lippert measurement point "A".

cw3jason · 01-02-2018, 10:47 AM

the pinbox flexing upwards is frame flex. The pinbox is welded to the frame, if it is moving the frame is flexing unless your welds are broken. that is what this measurement is for. you are just measuring in a different spot, so you get a different number. another possibility is your bolts are loose. there should be no movement from the pin box bolted to the frame.

prndl · 01-02-2018, 10:56 AM

Flex is here....
[IMG]

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cw3jason · 01-02-2018, 11:00 AM

If the pinbox is moving at the bolted connection that is not correct and should not move there. If it is just flexing up and down, that would be the entire frame that is moving and I posted how to measure that. The pin box does or should not move independently from the frame.

prndl · 01-02-2018, 11:07 AM

Bolts are tight. Three foot breaker bar tight!

CaptnJohn · 01-02-2018, 11:07 AM

Quote:

Originally Posted by cw3jason

If the pinbox is moving at the bolted connection that is not correct and should not move there. If it is just flexing up and down, that would be the entire frame that is moving and I posted how to measure that. The pin box does or should not move independently from the frame.

Agree ~~ 6 bolts should keep it tight.

dieselguy · 01-02-2018, 11:10 AM

Judging from your photo concerns ... you'll not like the Sidewinder any better. I have a friend that has an Open Range 40' fiver with the Sidewinder as he has a short bed Ford. It (Sidewinder) appears to bow when the fiver is sitting on his truck's hitch plate. He's pulled it a few thousand miles with no mechanical issue, but it sure looks concerning.

cw3jason · 01-02-2018, 11:10 AM

Quote:

Originally Posted by prndl

Bolts are tight. Three foot breaker bar tight!

Then you need to measure frame flex to see if you are within limits or you may have a broken weld. the whole upper deck flexes when hitched and that is what you see in the exposed pinbox. It would be more exaggerated out at the end of the pin box like you have measured, but Lippert needs the dimensions I gave you.

prndl · 01-02-2018, 11:21 AM

OK I will check it out in an hour.

prndl · 01-02-2018, 01:11 PM

OK, I just measured diagonal "A" measurement and it went from 70.5" to 71"

Additionally, the top of the pinbox is about 3/16" from the bottom of the plastic under belly and pushes up to press on the underbelly when lifted.

cw3jason · 01-02-2018, 01:18 PM

Quote:

Originally Posted by prndl

OK, I just measured diagonal "A" measurement and it went from 70.5" to 71"

Additionally, the top of the pinbox is about 3/16" from the bottom of the plastic under belly and pushes up to press on the underbelly when lifted.

frame flex sounds within spec, but the pin box moving enough to touch the underbelly may be an indication of a bad weld. you might want to bring it in and have the underbelly taken down and inspect the pinbox welds.

prndl · 01-02-2018, 01:25 PM

Thanks Jason.
I think I will take the underbelly down a little and see what's up.

What is the sealant used on the joints? It is clear and looks like silicone but it does not get dirty like silicone does.

cw3jason · 01-02-2018, 01:43 PM

I use Proflex rv caulk from the local RV store, but you can buy it other places

beeje · 01-03-2018, 05:58 AM

I was concerned about the movement in my 2011 3455sa pin box. I have one of those large levels mounted to it. Going down the road I can see quite a bit of movement between it and the front cap. I put a piece of tape on the side of the frame were the pin box is mounted to and marked a line on the tape using a spacer held against the bottom of the front cap. I then lowered the pin down on to a 6x6 post until the front jacks were off the ground. Using the same spacer I drew another line. The space between the lines is about 1/4 to maybe 3/8".

Also while the weight in on the pin, I looked around at the front of the bedroom closet area. The floor of the closet was pushing upwards on the dividing wall that divides the closet from the washer/dryer closet.

I then un-attached the wall from the floor and cut off about 3/8" off the bottom of the dividing wall panel.

I then secured a 3/4" x 3/4" stripe of 1x to the floor on each side of the panel, but not secured to the panel. Now the panel will just slide up and down in its slot.

I have not had any issues and think that things are normal. All steel has to flex somewhat or it would brake.

I also removed the trim on each side at the overhang and going down towards the ground. I cleaned the areas up and re-secured the trim after pumping a lot of clear silicon into that area.

Like I said I can still see some movement, But think it is normal and keep an eye on it.

Jlyons · 06-21-2018, 04:53 AM

I recently bought a new 362RD and noticed the divider wall in the front closet had a small crack at the bottom near the floor. When I took the measurement as described above I have 1/4inch flex. I feel that this is normal and in all reality if the divider wall Hadn’t been built all the way, very snug fit, to the floor it wouldn’t have split. I have no other signs of issues and agree that some flex is necessary otherwise to much rigidity would be more dangerous. For me I feel this is normal and will keep an eye on it. Going to trim the lower divider wall and add in a piece of matching stained trim across the bottom to give it a manufactured look.

The Bone · 06-21-2018, 07:26 AM

I had some flex from my pin box then it got worse and moved the wall in the front of my 5er. it was so bad that I didnt want to tow it anywhere. found out that all the welds on one side had broke. I had both sides welded and no more flex. Your hitch should be solid and no flex. If it moves back and forth enough times something will brake.

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