Porpoising with camper

[rskeans]

I have an Okanagan DBL117 truck camper mounted on an '08 6.4 DRW 4x4 w/camper package. OKANAGAN - Camper Floorplans Tie downs are Torklift. The camper is loaded and could weight 4800 lbs.

I get a 'porpoising' effect on the highway. This is evident by the camper overhang movement over the cab. The torklift tie dows are secured to the frame. The porpoising means that there is a spring-mass effect with the torklift tie downs with the spring being the torsion bars of the torklift and the mass being the camper. It also means that the truck bed is also flexing.

The truck bed is secured to the frame through some huge rubber gromets. It seems that the gromets must be flexing/compressing.

The question is - - Can the bed be hard mounted to the frame?? Doing so should remove the 'spring' portion of the spring/mass resonance.

Thanks,

[walleye1]

what you will need is a pair of struts that mount to the overhead of the camper and the other end to brackets installed to the truck where the fenders,hood and black piece of cowling come together, if your dealer dont have what you need see your local lance camper dealer and they will hook you up! this makes a HUGE differance!

[rskeans]

Originally Posted by walleye1

what you will need is a pair of struts that mount to the overhead of the camper and the other end to brackets installed to the truck where the fenders,hood and black piece of cowling come together, if your dealer dont have what you need see your local lance camper dealer and they will hook you up! this makes a HUGE differance!

Many thanks for your suggestion. I had not considered the struts. I have seen Lance campers with the struts, however, I do feel uncomfortable about the stress put on the camper at the point of the strut connection. I'll check with Okanagan about that detail.

[locrwln]

More importantly, unless they have made a signifigant change to the rear bumper on the 08's, you need to replace it with one made of thicker material. I could twist the stock rear bumper on my '02 by hand (I am a small guy).

I now have a Reunel rear bumper on mine and it made a huge difference on the camper movement.

I have a Lance 10' in my F350, no struts.

Jack

[Clattertruck]

The problem is frame flex that develops a harmonic from the road joints. I don't know all the dynamics. My single rear wheel trucks did it worse than the DRW trucks. My new F450 does not buck except slightly very occasionally. The G rated tires are rock hard. It weighs 14,400 lbs with camper.

The strut solution worries me because the cabover is subject to considerable stress, which over time may be bad. I don't think that the Tork Lift tie downs are a part of the problem. You might check the center of gravity point of the camper. If it is not slightly ahead of the rear axle, it could be a big part of the problem. Have you put the rig on a CAT scale to get the steer axle and drive axle weights?

The road builders in this country would do better to stagger the joints or do a better job in putting down concrete

[rskeans]

Originally Posted by locrwln

More importantly, unless they have made a signifigant change to the rear bumper on the 08's, you need to replace it with one made of thicker material. I could twist the stock rear bumper on my '02 by hand (I am a small guy).

Jack

The camper tie down is not tied to the bumper. The torklift tiedown is directly secured to the frame. Torklift Tie Downs
I think part of the problem is the flex in the torklift arm.

[Larry S.]

If you are using a full Tork Lift tiedown system there are springs designed into the system to allow some flex. Either in the tie down end piece or in the chain tightener. You don't want the camper tied hard to the frame. A little movement in the overhead is normal. Also the cab is mounted in rubber mounts and will move in relation to the bed and frame.

[rskeans]

Originally Posted by Clattertruck

The problem is frame flex that develops a harmonic from the road joints. I don't know all the dynamics. My single rear wheel trucks did it worse than the DRW trucks. My new F450 does not buck except slightly very occasionally. The G rated tires are rock hard. It weighs 14,400 lbs with camper.

The strut solution worries me because the cabover is subject to considerable stress, which over time may be bad. I don't think that the Tork Lift tie downs are a part of the problem. You might check the center of gravity point of the camper. If it is not slightly ahead of the rear axle, it could be a big part of the problem. Have you put the rig on a CAT scale to get the steer axle and drive axle weights?

First the F450 would have been a better choice for this application. But I've got the F350 to work with.

How do you have your camper secured??

I agree with the harmonic observation. I'm just not sure that it is frame flex. I think it is the harmonic between the torklift torsion arms, truck bed grommets installed between the truck bed and the frame, and the weight of the camper, which in reality is at the upper limit of the truck. I have installed air bags mainly to minimize my head lights from blinding oncoming traffic. I believe the air bags at maximum pressure (90#) makes it worse. I now just put in 30# for normal daylight driving. I rarely drive at night.

The camper has a center of gravity sticker which if fully forward in the truck would be exactly over the axle. However, if I mounted it fully forward the truck rear tail lights would hit the camper. So I mounted a 1" wood spacer (actually about 3/4") against the forward bed wall to prevent the camper from hitting the tail light. Therefore the CG sticker is about 3/4" behind the axle. The deciding factor could be if I have full tanks. The fresh water tank is 64 gallons and is forward of the axle. I also have a 62 gallon fuel tank that is mostly forward of the axle.

I haven't gone to the scales. Good idea though. I'm in the mountains and the scales are about 45 minutes away in the valley. I can do a before and after to show how much weight is being transfered to the front axle. I'll post back when I get the results. It could be awhile though.

I also worry about the strut solution. Maybe Lance has the strut mounting location reinforced since I see Lance campers with the struts all of the time.

[rskeans]

Originally Posted by Larry S.

If you are using a full Tork Lift tiedown system there are springs designed into the system to allow some flex. Either in the tie down end piece or in the chain tightener. You don't want the camper tied hard to the frame. A little movement in the overhead is normal. Also the cab is mounted in rubber mounts and will move in relation to the bed and frame.

Thanks for your input Larry. A couple questions.

1. Why don't I want the camper tied hard to the frame?

2. My overhead movement is at least a couple inches peak to peak on smooth roads. Hit a bump and wow. The camper resonance is about 1 cycle per second. That is a guess. I don't think the truck cab moves at that rate. I did note the cab rubber mounts.

[Larry S.]

1. Why don't I want the camper tied hard to the frame?

If the camper is tied hard to the frame you can overstress the camper tie down points and tie down chains. It might not be too bad if the chains were always cinched down tight but due to the flex in the camper and frame of the truck some slack will develop under rough conditions. The impact when slack is created and then taken out can rip out the tie downs, break the chains, straighten the tie down hooks or break something else in the camper. A little cushion is good. You probably won't experience any of these failures in normal driving but if things go bad you don't want a camper tie down failure. Some years back I had a rear chain fail in a hard tied system when I had to leave the road to avoid an accident. I now use larger than typical tie down chains with spring loaded chain tighteners along with Tork Lift front tie downs and a custom rear tie down. All chain connections are welded closed loops, no open hooks.

Having the box hard to the frame is OK but I doubt it will solve the problem.

Your movement does sound larger than I'd like. I'd guess the camper is nose heavy. It probably has a queen or king bed lengthwise in the overhead with oak cabinets and trim. I would suggest talking with Tork Lift to see if they offer a stiffer rear tie down. If they don't, consider a custom rear tie down that is incorporated in the rear receiver hitch frame. Tork Lift does offer an integral receiver hitch and tie down but I am unsure of its flex. My camper may move up and down a half inch at its nose in normal driving and never develops a rocking motion. While you have a much heavier camper than I, I probably have my truck proportionally overloaded more than you do.

[Blue Water Runner]

Originally Posted by rskeans

I get a 'porpoising' effect on the highway. This is evident by the camper overhang movement over the cab. The torklift tie dows are secured to the frame. The porpoising means that there is a spring-mass effect with the torklift tie downs with the spring being the torsion bars of the torklift and the mass being the camper. It also means that the truck bed is also flexing.

This is a very normal thing for about any truck camper. The flex is in the trucks frame and the Tork Lift brackets that attach to the frame. You do not want to have the camper too rigid otherwise a jolt such as a pot hole could rip the eyelet out of the bottom of the camper. Make sure that the spring loaded tie downs are located at the front of the camper. The rear tie downs are not spring loaded. My camper moves up and down constantly while underway. Don't worry about it its not going anywhere so long as you have a rubber mat under it. Make sure you have enough clearance around your amber cab clearance lamps. I have 3 treated 2x4s and a sheet of 3/4" treated plywood screwed into the frame of my camper. I have Tork Lift tie downs also. Click on the link in my signature for a picture of my rig.


You may want to invest in a set of air bags or timbrens for that load. Good luck.

Here is a forum that may be helpful to you: NATCOA FORUM

[walleye1]

rskeans, Did you come up with anything to solve your issue? if you havent you should check into cab struts, all it is is a extra long light weight shock absorber that takes the harmonics out of it, makes a huge differance! it wont put any extra stress on cabover that it cant handle, its not "solid" by any means, let us know what you find please, thanks

[rskeans]

Originally Posted by walleye1

rskeans, Did you come up with anything to solve your issue? if you havent you should check into cab struts, all it is is a extra long light weight shock absorber that takes the harmonics out of it, makes a huge differance! it wont put any extra stress on cabover that it cant handle, its not "solid" by any means, let us know what you find please, thanks

A couple things have taken place.
I discussed the problem with a local spring shop. They suggested the truck was overloaded and to add springs. The truck does have air bags. Then just yesterday I noticed that an air bag bracket had sheared its bolts. The bracket had bottomed out and sheared the bolts. I didn't know that had happened, but I remember the incident coming out of an RV park driveway, turning right and a loud bang when the rear wheels hit the gutter. I didn't see the bracket during the inspection of what I heard.

The bracket was fixed today. However, I note that the distance to bottoming out is only 3.5". The trucks overload bumper is 5.5"! Wow. This seems like a problem. So, the jury is still out. I'm going camping Oct 12 and I'll know more at that time.

Regards,

[Blue Water Runner]

Originally Posted by rskeans

A couple things have taken place.
I discussed the problem with a local spring shop. They suggested the truck was overloaded and to add springs. The truck does have air bags. Then just yesterday I noticed that an air bag bracket had sheared its bolts. The bracket had bottomed out and sheared the bolts. I didn't know that had happened, but I remember the incident coming out of an RV park driveway, turning right and a loud bang when the rear wheels hit the gutter. I didn't see the bracket during the inspection of what I heard.

The bracket was fixed today. However, I note that the distance to bottoming out is only 3.5". The trucks overload bumper is 5.5"! Wow. This seems like a problem. So, the jury is still out. I'm going camping Oct 12 and I'll know more at that time.

Regards,

I would look at only adding leafs to the overload. What brand of airbags are you using? Are they installed correctly?

[rskeans]

Originally Posted by Blue Water Runner

I would look at only adding leafs to the overload. What brand of airbags are you using? Are they installed correctly?

I agree with adding the springs only in the overload.

The airbags are Firestone Ride Rite 2071. I checked the installation against the Firestone installation instructions and they are right on.

The problem is the Firestone upper bracket hitting the Firestone lower bracket with heavy load and a bump in the road, driveways, speed bumps, etc. I didn't notice this interference problem or the difference of height in the Ford overload bumper until I got it home yesterday. It appears to be a Firestone design problem. The next time I load the camper on the truck I'll take it to the shop (located down the mountain) and let them comment on my observation. In fact, maybe I'll just do it today. The shop is well respected and used by local RV dealerships, County and City Gov't dept's, etc. I'm in San Bernardino County and yesterday I noted a Los Angeles County vehicle in the shop. The LA County line is about 35 miles away.