Scamp 5th wheel "bucking" on uneven surface ?

[Westcliffe01]

So I spent my weekend driving from SE MI to NE Iowa to pick up my "new to me" 19' 5th wheel trailer. It has some faults, but the price was reasonable and it is a good base to work from.

I reported earlier when looking for a hitch that I settled on the Andersen "ultimate 5th wheel connection".

It is really a bit high, even for one like what I bought which has been raised and that is mainly due to the ride height of my F250 in 4x4 format. I would not particularly want to reduce the clearance between the front end of the trailer and the bed.

In general, towing was completely satisfactory except for 2 issues:
1) When driving on surfaces that have a repeated undulation (concrete roads cast in strips or which is worn out) the trailer had a tendency to convert the vertical road condition into a forward and backward shunting motion. It was clearly a resonant behavior since the amplitude would become larger and larger until my 7800lb curb weight truck was being shunted pretty good which would cause a terrific stress in the hitch and the 5th wheel structure and its attachment points. If I looked in the mirror, I could see the vertical hopping of the trailer, so I am guessing that in conjunction with the rubber mounted trailing arm that this vertical motion is being converted into a horizontal motion and then feeding upon itself ?

2)I did notice that it took a long time for the trailer to settle after a bump. If would oscillate up and down and sometimes side to side (if the bump just hit one wheel). So I am assuming that this trailer like most others has no shock absorbers to provide damping ?

I think 1 and 2 are related and wonder if I should try to fit shock absorbers or try to make a clean break and just convert to leaf springs instead ? With the amount of clearance my trailer has, fitting a straight 3500lb axle should be very simple and they are available very cheap on the surplus market given my proximity to northern IN (center of the RV universe).

Thoughts ?

[Donna D.]

Keith, I've looked at your prior posts and your profile doesn't say.. what year Scamp?

[Westcliffe01]

I believe it is a 92. Title is still in my truck and I'm taking a break after a 1100+ mile trip... I can report that I got 17.1mpg empty going out (west) and then averaged 13.5mpg on the way back (east). This is with a 2008 Ford 6.4 diesel. The truck towed great, other than the surface related issue it was very responsive, no sway whatsoever (as expected) so a lot less "white knuckling" that what I have experienced on I80 in the past.

[Donna D.]

Get some rest. Someone will be along shortly to give you some ideas to consider.

[Cyndi B.]

Is the Scamp axle raised for your truck?

[Westcliffe01]

This picture from prior to the sale shows the height relative to a half ton truck. Mine being a 3/4 ton and 4wd makes it higher to the surface of the bed.

[Eddie Longest]

Keith
A 21 year old Tork-flex type axle is more than likely at or near the end of it useful life. When these type of axles get old they loose their dampening effect. On a good axle each side works independent of each other and that prevents road issues being transferred from one side of the trailer to the other.
In a regular trailer your hitch is almost level with your axle so when you hit a bump on one side your hitch wants to raise up half the height of the bump. With a 5er your hitch is about 30" above the axle. So when you hit a bump on one side the hitch wants to rise up but it also wants to push away from the raised side of the trailer. With a dead axle you tend to get a jerky ride.
Once you change the axle out your first impression will be the trailer is floating down the road behind you. I think you have a dead axle and all the bumps in the road are not being dampened and that's why you are getting a jerky ride.
If you have Dexter axle (square tube) you can give them the info. off of your data plate and they can tell you what your arm angle should be. You can go to their charts and determine the max. deflection. If the axle is near or at its max deflection then it axle replacement time.
Eddie

[Eddie Longest]

Keith
Also with the high 5er hitch when the trailer bounces it also want to give you a little more push/pull action with its bounce. That's where the bucking comes from.
Eddie

[Brian B-P]

Originally Posted by Westcliffe01

2)I did notice that it took a long time for the trailer to settle after a bump. If would oscillate up and down and sometimes side to side (if the bump just hit one wheel). So I am assuming that this trailer like most others has no shock absorbers to provide damping ?

I think 1 and 2 are related and wonder if I should try to fit shock absorbers or try to make a clean break and just convert to leaf springs instead ?

Right, you are seeing a lack of damping. No stock Scamp (or any other moulded fiberglass trailer built in North America with rubber-sprung suspension) has shock absorbers, but the rubber is inherently somewhat (but not enough to be ideal) self-damping.

You can downgrade to a beam axle on leaf springs to make shock installation easy, although some people have added shocks to the rubber-sprung independent suspension. Unfortunately, there is no longer a do-it-yourself kit for this retrofit (Monroe used to make one years ago); however, Airstream still adds shocks to all of their trailers which currently (or at least recently) use Dexter Torflex.

Originally Posted by Eddie Longest

Keith
A 21 year old Tork-flex type axle is more than likely at or near the end of it useful life. When these type of axles get old they loose their dampening effect.

Mostly they lose their springing (collapsing to an always-compressed state), but that's a good point -it would reduce or eliminate the damping as well.

[Jared J]

Mines a fifth wheel with a new axle. It will do it, but rarely, and never enough to worry about. The stretch of road two miles from my house is the worst.

[peterh]

A couple of thoughts for you. The first is that your axle may be reaching the and of its useful life, and, as others have already observed, an old axle loses its shock-damping qualities.

Another thing to consider is your weight distribution and how well your trailer is loaded. Traditional bumper-hitch philosophy is to have a minimum of 10% of the trailer's total weight resting on the hitch. 5th wheel, gooseneck, and similar arrangements are usually double that weight.

When I look at your trailer photo, it looks like you're hauling four trail bikes that likely weigh 35-40lbs each or more plus the weight of your bike rack, 200lbs of weight hanging way out there at the far end of your trailer, all of it taking weight off your hitch. Top off your water tank, and you might well be below even the 10% standard hitch weigh for bumper towing.

Sway isn't as much of a problem with 5th wheels as it is with bumper hitch trailers that haven't been balanced properly. Instead of sway, you get something like that "oscillating" pattern you described.

You might consider loading up your trailer and tow vehicle and take them past an closed highway truck scale. Weigh your truck's four wheels while hitched to the trailer, then the two wheels of the trailer, then disconnect and weigh the truck again, than use this formula:

(truck with trailer weight) - (truck's unhitched weight)
---------------------------------------------------------------------------------------------
(trailer axle weight) + (truck with trailer weight) - (truck's unhitched weight)

For example, my tow vehicle weighs 3500lbs packed and ready to go, but not yet hitched to our Scamp 5er. When hitched, the weight on my four truck tires is about 4200lbs, and my trailer's axle weight, hitched and ready to roll with full water and propane, is 2800lbs.

( 4200 lbs - 3500 lbs ) / ( 2800 lbs + 4200 lbs - 3500 lbs ) =

( 700 lbs ) / (3500 lbs) = 0.20

That's 20%, so 20% of my trailer's total weight is sitting on the hitch.

[Jared J]

It's possible, but I have 40 gallons of fresh water at the back of the camper, which is is 372 pounds, and I have little trouble. The thing that gets me is a series of ridges in the road by me that seems to be perfectly spaced to the suspensions rebound.

[Westcliffe01]

Jared, I think the only way to avoid a critical resonance is to add damping. The trailer is at a local RV shop getting the AC removed and 2 roof vents (unusually large sizes) replaced since they are past due at 20+ years old. I'm putting in a 3rd vent instead of the AC since that is a standard sized 14" hole.

Trying to get it fully weather tight for the winter, then will demo the interior in the spring. Mostly tear out the insulation/lining, which is sagging and the flooring - carpet - yuk...). Put in a diesel heater and figure out if retrofitting a bathroom is feasible. Install batteries and solar panels for off grid operation (9000+ feet in the rockies)

Then I will have to work on the door, which has been thoroughly messed up (PO put in a 3/8" thick hard rubber gasket all the way around and that totally sprung the door out of shape and it is full of stress cracks at the hinges...) Joy joy...

I have read through your renovation project and mine is not going to be showy, just functional. I will probably replace all of the sleeping area windows with much smaller portholes and insulate that area a bit better. Will similarly fit smaller double glazed windows in the rest of the coach since this is going to a colder climate. Have not quite settled on a strategy for insulating the hull. I am thinking of using scored foam sheet which should conform to the contours if one works with a small enough area at a time ("planking" with foam cut about 1.5" wide is one way). Then lay a couple of plies of BID over the top of that (all bonded with epoxy) and finally paint the inside with one of those roll on bedliner type materials.

No rat fur in my future.... Have to work out ideas for longer term boondocking storage space. A single closet is not going to work. I will also be building a laundry / bath house that will fit on my equipment trailer for transportation (20ft x ~ 8 ft wide) but will not be expected to be very mobile... That will house the diesel genset, water heater, 100gals of water, washer, dryer, office space, guest quarters... sounds like it is getting pretty busy already....

[Westcliffe01]

The picture is of the previous owners setup, not mine. The bungee cord to the bikes has cracked the flange on the shell on both corners. I also took off the spare wheel since only 2 attachment bolts were holding and it wiggled side to side. This trailer has not had water in the built in tank for more than 10 years so that was also not an issue.

I'm sure the comments regarding this having a 20 something year old axle are probably correct. I personally have never thought leaf sprung axles were too harsh, assuming of course that you were using them near rated load. Of course, if one uses a 5000lb set of springs on a 3000lb trailer then it will probably not be the best. This 3500LB BRAKE AXLE 86 HF 68.5 SC 5-LUG TRAILER,CARGO


is a typical offer for northern IN/SW MI. a 3500lb straight axle with brakes and springs for $200. The store sells spring seats, so if one needs extra clearance one can weld the seats on top of the axle and not have to make tall spring mounts and shackles. I have thought of using a short mount for the leading edge of the spring and a long one for the back, to try to keep the spring movement perpendicular to a line from the axle to the center of the hitch ball.

I guess I have all winter to think about it (no barn to work on my RV in the off season).

Originally Posted by peterh

When I look at your trailer photo, it looks like you're hauling four trail bikes that likely weigh 35-40lbs each or more plus the weight of your bike rack, 200lbs of weight hanging way out there at the far end of your trailer, all of it taking weight off your hitch. Top off your water tank, and you might well be below even the 10% standard hitch weigh for bumper towing.

[Brian B-P]

Originally Posted by Westcliffe01

I have thought of using a short mount for the leading edge of the spring and a long one for the back, to try to keep the spring movement perpendicular to a line from the axle to the center of the hitch ball.

I see the logic, but I wouldn't do that.

When a beam axle on a leaf spring moves vertically, it also moves forward or backward slightly. When it tilts (because the vehicle is leaning such as in a turn or sway oscillation), the difference between left and right vertical travel causes different fore/aft movement... that means the axle steers. If the front mount of the spring is lower than the rear, it steers into the turn, which is good for stability; that's why trucks have their rear leaf springs noticeably sloped front-down.

Longer mounts on the rear would slope the springs the wrong way for stability. I suspect that just shocks would make a significant difference.

[Paul O.]

My take on the bouncing problem is that the tire inflation has a lot to do with it. I towed my 2004 Scamp 19' to Vermont after buying it used in Delaware last February (first time towing anything!). The tires were low and I was not sure about the right pressure, so I pumped them up to 30psi. I was quite worried about the front to back chucking and seeing the trailer bouncing in the rear view mirror. Then I discovered that the right pressure is 45psi (posted on the VIN sticker on the frame). Inflating them to 45psi changed the resonant frequency of the system and made a huge difference in driving comfort. After that I stopped looking into the shock absorbing hitches.