Forum Discussion

RussOnTheRoad's avatar
RussOnTheRoad
Explorer
Mar 20, 2016

Pin Box vs. Truck Bed Wall: How to Avoid Conflict?

I'm learning about 5th wheels and trucks, thinking about taking that plunge after I sell my Class C.

I've heard about an issue where somebody with a fiver had a problem: when making tight turns his pin box would hit against the truck bed walls and he was not able to fix this with the standard adjustments.

When I heard about that it started me thinking about all the things I don't know about pin boxes, hitches, trucks etc. How can I be certain to avoid the same problem this other gent had? My first thought was that with any fiver or truck I'm considering I should take some measurements. For the fiver I should measure from the ground up to the lowest point on the pin box and on the truck I should measure from the ground to the highest point of the truck bed wall. Perhaps it would be more important to measure from the pin of the pin box to where it attaches to a given hitch? (I suppose tailgates can be a problem too but I've seen fixes for that.) What is the rule of thumb about how much clearance there should be between the pin box and truck bed walls? How should I be thinking in regard to pin box/hitch/truck bed wall height? Is there a primer somewhere that covers stuff like this that a fiver wannabe like myself can refer to?
  • SanMarMor's avatar
    SanMarMor
    Explorer
    Mar 21, 2016
    RussOnTheRoad wrote:
    SanMarMor wrote:
    On our 5er, the body of the pin box is down inside the bed sides. And the length of the pin box is such that on a very tight turn, it can contact the bed sides. But this is a very tight turn, and once I knew it would do it, I can easily avoid the situation. Haven't gotten into any situations where I "had" to turn tight enough it would contact the rails.


    Is that common? To be expected?


    I don't know how common it is. This is our first 5er.

    I do have 6" rail clearance, but because of the depth and length of our Trail Air pin box, it can hit the side of the bed when turning very tight.
  • RussOnTheRoad's avatar
    RussOnTheRoad
    Explorer
    Mar 20, 2016
    SanMarMor wrote:
    On our 5er, the body of the pin box is down inside the bed sides. And the length of the pin box is such that on a very tight turn, it can contact the bed sides. But this is a very tight turn, and once I knew it would do it, I can easily avoid the situation. Haven't gotten into any situations where I "had" to turn tight enough it would contact the rails.


    Is that common? To be expected?
  • RussOnTheRoad's avatar
    RussOnTheRoad
    Explorer
    Mar 20, 2016
    valhalla360 wrote:
    It is unclear which problem you are talking about:
    - If you jackknife the trailer far enough, the main body of the 5er can hit the cab of the truck. Two solutions: Get a long bed or get a sliding hitch. You can still hit the cab but you have to do a pretty extreme turn.
    - If the truck bed is too high, the 5er overhang will be too close to the bed rails. If the trailer wheels on one side drop into a hole, the overhang can hit the bed rails. Usually, you want at least 6" space. The simple solution is to adjust the hitch and pin box to maintain at least 6" space. The problem is if the truck is too high, the trailer won't ride level. The solution to this is to put the axles under the leaf springs. If that doesn't give you enough to level the trailer, you are looking at full on frame modification and at a point, the trailer is just too high.
    - The other possibility is during a sharp turn while backing, the pin box could hit the bed rail. Never had an issue with it but could see if the trailer is at a 90 degree angle to the truck and the trailer is dropping down as it leaves the roadway. Not sure how to fix but not a common issue.


    The problem I was asking about was the pin box hitting the rails, but you mentioned a general rule of thumb that will be useful to me and anybody else shopping for a fiver: 6" clearance between the rails and fiver. How does one make sure of this berore they purchase? Are there measurements that can be made of the fiver, pin, hitch, truck bed height, rail height? That's the question. What can be done before buying to avoid problems?
  • SanMarMor's avatar
    SanMarMor
    Explorer
    Mar 20, 2016
    On our 5er, the body of the pin box is down inside the bed sides. And the length of the pin box is such that on a very tight turn, it can contact the bed sides. But this is a very tight turn, and once I knew it would do it, I can easily avoid the situation. Haven't gotten into any situations where I "had" to turn tight enough it would contact the rails.
  • valhalla360's avatar
    valhalla360
    Navigator
    Mar 20, 2016
    It is unclear which problem you are talking about:
    - If you jackknife the trailer far enough, the main body of the 5er can hit the cab of the truck. Two solutions: Get a long bed or get a sliding hitch. You can still hit the cab but you have to do a pretty extreme turn.
    - If the truck bed is too high, the 5er overhang will be too close to the bed rails. If the trailer wheels on one side drop into a hole, the overhang can hit the bed rails. Usually, you want at least 6" space. The simple solution is to adjust the hitch and pin box to maintain at least 6" space. The problem is if the truck is too high, the trailer won't ride level. The solution to this is to put the axles under the leaf springs. If that doesn't give you enough to level the trailer, you are looking at full on frame modification and at a point, the trailer is just too high.
    - The other possibility is during a sharp turn while backing, the pin box could hit the bed rail. Never had an issue with it but could see if the trailer is at a 90 degree angle to the truck and the trailer is dropping down as it leaves the roadway. Not sure how to fix but not a common issue.
  • RussOnTheRoad's avatar
    RussOnTheRoad
    Explorer
    Mar 20, 2016
    retispcsi wrote:
    First what truck are you talking about Ram, Ford, Chevy and is it a long bed or short bed. As far as rail height there are many ways to manage that. A long bed you should not have cab damage. A short bed you may want a slider. Also what fiver are you looking at?


    I'm not talking about any truck, hitch or fifth wheel in particular. I'm asking how a person can avoid running into the problem mentioned (or others) by knowing how to avoid it before a rig, hitch or truck is purchased and using that knowledge to make sure he isn't setting himself up for problems.

    Also, I'm not talking about the bed or tailgate hitting the fifth wheel (although that's obviously something else somebody should think about). I'm talking about the pin box hitting the bed rails during sharp turns.
  • RussOnTheRoad's avatar
    RussOnTheRoad
    Explorer
    Mar 20, 2016
    transamz9 wrote:
    Jack_Diane_Freedom wrote:
    Get a SuperGlide slider hitch and there is not problem.


    That is not going to solve what the OP is talking about. My 5ers pin box has a plastic cover over it that hits the inside of my bedrails when back into tight spots.

    OP , I had to trim the lower back corners of my trim and pin box mount.


    What trim was that?
  • transamz9's avatar
    transamz9
    Explorer
    Mar 20, 2016
    Jack_Diane_Freedom wrote:
    Get a SuperGlide slider hitch and there is not problem.


    That is not going to solve what the OP is talking about. My 5ers pin box has a plastic cover over it that hits the inside of my bedrails when back into tight spots.

    OP , I had to trim the lower back corners of my trim and pin box mount.
  • retispcsi's avatar
    retispcsi
    Explorer
    Mar 20, 2016
    First what truck are you talking about Ram, Ford, Chevy and is it a long bed or short bed. As far as rail height there are many ways to manage that. A long bed you should not have cab damage. A short bed you may want a slider. Also what fiver are you looking at?

About Fifth Wheel Group

19,008 PostsLatest Activity: Mar 15, 2025