how much pin box movement is normal?

[alexleblanc]

I see this posted somewhat but I can't get a clear answer - my unit it still basically new I noticed that then I hook it up the distance from the bottom of the front cap and the pin box (checked pin box torque and its right on)gets closer by about 3/8" - 1/2" and while driving I can see about another equal amount of movement - I have one of those pin mount RV levelers mounted up there and its actually slightly scraped on the bottom of the front cap and the measurement is exactly 5/8" as far as I can tell.

I'm going to hook up the truck tonight and take some pictures and measurements.

here's a picture of the said level gauge that really helps me see the movement:



Alex

[laknox]

larry barnhart wrote:
From what has been posted on rv.net I would not take what Lippert feels is ok to be a fact.

chevman

ROFLMAO!

Lyle

[larry_barnhart]

From what has been posted on rv.net I would not take what Lippert feels is ok to be a fact.

chevman

[alexleblanc]

took the measurements from the points that the Lippert sheet stated and I'm getting less than 1/8" from sitting on the landing gear to sitting on the hitch in difference on one side and 1/4" on the other side.

this is the form I'm referring to:
http://rvman.net/temp/LippertUpper-Deck-Flex-Measurement-Instructions.pdf

[ckwizard777]

If I had 1/2 of pin box movement I would re-build the entire pin box area with 1/4 wall tubing, There is no way 1/2 plus is normal.
Mine moves about 1/8 inch and I would prefer that it diddnt move at all.
Of course extended pin boxes make the problem even worse by providing a giant lever action to your front frame.
You should investigate why you are seeing that much movement.

[Retired_JSO]

Should have no or very little movement. I noticed our, when new, 2004 Sandpiper pin box wasn't moving but the front cap was. It was opened up and found the screws used to hold the sidewalls to the frame had never been installed. Well we fixed that problem and while in there, beefed up the sorry build by bracing the overhang and pin box attachment.

[Old-Biscuit]

1/4" to 3/8" FLEX is what NUWA stated would be considered normal when I questioned them about movement I was noticing.

Took my 5vr into them .......they found pin box structure/supports were solid but drivers sidewall bolt was broken allowing off-set side to side difference
(Curb side no excess movement---roadside had 5/8" movement when hooking up)

They 're-bolted' sidewall to overhang frame by adding extra bolts in a 'W' pattern

So if you have change in measurements from hooked up (all weight on hitch) to unhooked (weight on front landing gear legs) then a Visual Inspection is advisable.
Remove overhang panel/cover and check ALL braces/cross members/pin-box/sidewall for movement and/or cracks/stresses hooked/unhooked

[BB_TX]

I also have the 5th Airborne. The top part of his pin box where his level is mounted is bolted rigidly to the frame and should not flex. It is the lower plate where the king pin is attached that does the flexing.

[alexleblanc]

just spoke to my dealer service guy, he pulled out the Lippert upper deck frame flex info and offered to measure it for me or let me do it myself. I told him about the movement I had been seeing and roughly the measurements. He was not overly concerned as that seems to be inline with what Lippert and some of the manufacturers alow for. He did ask me about any caulking that was cracked or cracking, cracks in the fibeglass or any of the interior panels/cabinets or elsewhere. I checked everything very carefully on Monday and could not see anything that was out of place.

I'll take the measurements and follow up with him so he can see what KZ says.

[N-Trouble]

He's referring to frame flex, not pinbox. His 5th Airborne has nothing to do with whats being discussed. The same frame flex would be there with a rigid pinbox.

[Flapper]

You have a 5th Airborne, which uses essentially an airbag in the pin box to minimize road shocks. It is adjustable by adding/removing air pressure. See the manual. It sounds like you may need to add more air, and that some up/down movement is to be expected so that you don't have as many road shocks transmitted to the tow vehicle. Call Reese first to verify whether the amount you observe is normal, and what adjustments they suggest if it is not.

[N-Trouble]

I would say normal. Metal flexes... Nothing is entirely rigid on any trailer so some amount of flex (1/2" or so) is expected. More than in inch I would be a little concerned. I had the exact same situation where my level (mounted in exact same spot as yours) made contact with the bottom of front cap while towing. Bout 1/2" gap while sitting unhooked.

Most just don't notice the movement/flex but since you have your level there it becomes more apparent.

[fj12ryder]

AFAIC there should be no movement. Any movement indicates flex somewhere and that means it isn't as solid as it should be. The amount of movement you've indicated points to a problem, maybe not serious yet, but as things flex, bend, and fracture it will surely get worse.