Frame Sag

Bluedog225 · Jan 17, 2009, 07:04 PM

I am looking at used pop ups and one thing keeps coming up. Several seem to have the long underside frame members sag over the axle. Not a lot. If I were to pull a string from one end of the trailer to the other, each end would be about 1/2 to 1 inch below the center (the part resting of the spring brackets).

I expect a little sag but this seems indicative of an issue with the integrity of the frame.

Is this a problem? Seems like one to me. Can it be fixed? Or is the trailer frame permanently damaged?

Thanks

Tom

tlhdoc · Jan 18, 2009, 10:55 AM

I don't know what brands of PUs you have been looking at, but the frames on PU trailers are not very strong. They do flex and bend to some extent. They are made light weight, hence the flexible frame.

JohnandLeann · Jan 18, 2009, 02:38 PM

I have been curious how to go about measuring the frame sag on our own rig.
It is very obvious to me that it does not sit straight. Kinda like it has been rung out like a rag, twisted. Guess I could try to figure which side is up or down by using the string method mentioned here. hhmmmmm.

Bluedog225 · Jan 18, 2009, 04:25 PM

Quote from: JohnandLeannI have been curious how to go about measuring the frame sag on our own rig.
It is very obvious to me that it does not sit straight. Kinda like it has been rung out like a rag, twisted. Guess I could try to figure which side is up or down by using the string method mentioned here. hhmmmmm.

I think the easiest way is going to be the 99 cent bullet levels with magnets from Harbor Freight. Just put one on the frame and level with tongue jack. then move it to the back of the pu. That should show you whether it is level or not. A 4 foot level will tell you how much you are off. Works front to back and side to side.

JohnandLeann · Jan 18, 2009, 09:53 PM

I think that is the level that I have already. Use it to level pup when setting up at camp site. Fairly sure it is magnetic type.

haroldPE · Jan 18, 2009, 11:04 PM

seems like it would be tough to really figuring it out with a level. if you have a surveyor friend (or contractor with a laser level), that would be the way to go. could measure from the laser reference plane to multiple points on the frame.

flyfisherman · Jan 19, 2009, 02:53 AM

Quote from: tlhdocI don't know what brands of PUs you have been looking at, but the frames on PU trailers are not very strong. They do flex and bend to some extent. They are made light weight, hence the flexible frame.

Can you be more specific?

ALL frames for trailers are made for flexing. Otherwise how could they possibly travel down uneven road surfaces? But where did this myth that PU frames are not very strong get started? Starcraft's tech services say that PU frames (at least Starcraft's) are as strong proportionally to any trailer made, be it a TT or 5th wheeler. Obviously my 8' box Starcraft does not have as strong a frame as in main frame size as does a 28' 5th wheeler but then it does not have to be. For what it has to do and it's GVWR it is more than adequate. When I was going to mount a bike carrier on the rear of the PU and attach it to the main frame rails and posted it here I remember the responses saying the frame was not strong enough. Well did so anyway and that was 7 years ago and I've hauled two bikes over a lot of the country side and to date have experienced no frame problems.

Fly

tlhdoc · Jan 19, 2009, 06:32 AM

Quote from: flyfishermanCan you be more specific?

If the frames are so strong why can't use leveling jacks to level youe PU? Why do they direct you to use a jack as close to the axle as possible, when changing a tire? The frames are not strong. You said it yourself Fly, they are not as strong as the frame on a larger trailer. They don't have to be, just like you said. They only have to be as strong as the job they are intended to do and that is support a light weight PU.

coach · Jan 19, 2009, 07:58 AM

FWIW, I believe your 8' box's frame members are as strong or stronger due to their short length.
The cross members are not as strong as the main beams.
Put a jack on the main beams is the recommendation, near the axle so it don't sea saw!
The longitudinal strength of a PU trailer is high, side to side it is weaker (where the stabs are). Some lift systems are part of the frame, since the stabs twist in the weak direction, this can cause 'premature wear' to the lift system.
Not all PUs are the same, neither are other trailers!

QuoteI expect a little sag but this seems indicative of an issue with the integrity of the frame.

Is this a problem? Seems like one to me. Can it be fixed? Or is the trailer frame permanently damaged?

I wouldn't be happy with any 'sag' of the 2 boxed main beams.

flyfisherman · Jan 19, 2009, 08:00 AM

Quote from: tlhdocIf the frames are so strong why can't use leveling jacks to level youe PU? Why do they direct you to use a jack as close to the axle as possible, when changing a tire? The frames are not strong. You said it yourself Fly, they are not as strong as the frame on a larger trailer. They don't have to be, just like you said. They only have to be as strong as the job they are intended to do and that is support a light weight PU.

It is the frame extensions that come off from the main frame (or frame rails) that are not strong enough to hold the entire weight of the PU, such as jacking on a corner. However, you can jack all day long on the main frame and the admonishment to jack as close to (and just behind) the axle is to make certain to keep the trailer tongue in it's normal down ward position.

The RV industry in general does what it can to keep the weight of the unit down, including a TT or a 5th wheeler, and not just popups. To make a general statement that PU "frames are not strong" may be your opinion but it is not based in fact.

tlhdoc · Jan 19, 2009, 10:05 AM

Fly why shouldn't you level the PU using leveling jacks? Why do you need to use wood, plastic blocks, tire levelers, or some other device to level the PU? Aren't the frame extensions part of the frame or are we now talking about just part of the frame???

coach · Jan 19, 2009, 10:14 AM

Quote from: Bluedog225Several seem to have the long underside frame members sag over the axle. Not a lot.

When (who, why) did this discussion vear away from the 'long underside frame members over the axle'? :confused:

flyfisherman · Jan 19, 2009, 11:28 AM

Quote from: tlhdocFly why shouldn't you level the PU using leveling jacks? Why do you need to use wood, plastic blocks, tire levelers, or some other device to level the PU? Aren't the frame extensions part of the frame or are we now talking about just part of the frame???

Do we not call those "stabilizers" ... and their intended purpose was to stabilize the camper after it had been leveled? Now I've been told (and really don't know) that at one time popup campers actually had leveling jacks and were used to level the camper along with instructions given to use them to change a tire if need be. To answer your question as to whether or not the frame extensions are part of the frame I would have to answer "yes", however, certainly not the stong part, only to support the wall structure. No doubt the entire frame work could be made stronger than it is but first off that would add weight (and certainly cost).

Consider this: a fishing friend recently went to a 22' TT with a dry weight of 3,800 lbs and a GVWR of 5,000 lbs ~ now if you were to take a peekie-boo under neath the TT you would see two 4" tube frame rails running the length of the camper, much like you see with your present Coleman/Fleetwood. Perhaps they are braced better for the extra weight ... I really don't know. Also, my neighbor down the road has a huge 38' Jayco 5th wheeler; has a dry weight at 11,000 lbs with a GVWR of almost 16,000 lbs - and it sports 6" main tube frame rails. My question to you would be how do you think one of these campers (yours included) would fare if they got into a high stress twisting situation on the road? I'm betting your Coleman popup would come out better! Getting back to my point, popup campers (at least the reputable ones), are designed frame strength wise, proportionally to their size and GVWR, as any production line TT or 5th wheeler. May be some "special mades", but they would be the exception.

Fly

wavery · Jan 19, 2009, 12:23 PM

Quote from: Bluedog225I am looking at used pop ups and one thing keeps coming up. Several seem to have the long underside frame members sag over the axle. Not a lot. If I were to pull a string from one end of the trailer to the other, each end would be about 1/2 to 1 inch below the center (the part resting of the spring brackets).

I expect a little sag but this seems indicative of an issue with the integrity of the frame.

Is this a problem? Seems like one to me. Can it be fixed? Or is the trailer frame permanently damaged?

Thanks

Tom

Hi Tom,

I would think that if the frame were "Sagging" in the middle (on both sides), this may not be problematic. In fact, the frame may well be bowed slightly for strength. Sorta like a bridge is bowed. However, I have no proof of that on these trailer frames.

I do know that large truck trailer frames are bowed upward in the center to allow for large loads to be centered on the trailer bed. However the stresses are different on these frames.

If the trailer frame is only bowed on the door side, this could be an issue. The door side of the frame has far less strength than the other side, as the other side has a fully framed wall for strength. The door side relies totally on the frame for strength.

Is it a big issue?

?? It is if the door doesn't fit properly. If the door fits properly, it really shouldn't be a big issue IMO.

flyfisherman · Jan 19, 2009, 01:54 PM

Quote from: waveryIf the trailer frame is only bowed on the door side, this could be an issue. The door side of the frame has far less strength than the other side, as the other side has a fully framed wall for strength. The door side relies totally on the frame for strength.

Is it a big issue??? It is if the door doesn't fit properly. If the door fits properly, it really shouldn't be a big issue IMO.

Good point, Wayne ~

Before I bought my present Starcraft I was "moon struck" with a '98 series Starcraft (the model I cannot remember) that was not picked up again in '99 and '00, where the door was to the rear of the camper. I thought they looked so neat! Also, Jayco, Coleman and Rockwood had this style at one time, too. I was to ask the Starcraft tech rep later why they did not continue with this rear door model and he said they were prone to sag at the rear ... there was not the wall strength needed to support the door opening. There was one board member (someplace) that had a rear door Rockwood with the sag and his first remedy was to jack the camper up on that door end! He said he got it about at the right place and then went to a welder who welded in a brace there, underneath the floor.
Have no idea if that fix was a permanent success.

Fly

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Frame Sag