Truck Bounce

[Jim_Carolyn]

I just bought a 2015 Arctic Fox 811S camper and have it mounted on a GMC Denali 3500, crew cab, 4WD with a standard box (6.5'). I also have installed air bags on the rear.

On my drive home from the dealer, I noticed that every-time I hit a rough spot in the road, the front of the truck started bouncing or as a guy at the dealer called it "Dolphining" (like a Dolphin going in and out of the water). He suspects that the air is lifting the front end of the camper slightly and therefore lifting the truck. After a couple of bounces it then stops and on smooth roads it doesn't bounce.

I had the maximum amount of air in the air bags and the rear seemed fine until I let some air out of the bags to test that then the rear started bouncing also.

I have Rancho shocks on the truck now but the dealer said maybe I should buy adjustable Rancho shocks for the front end. Another guy told me he had that problem (years ago) and bought a large air bag (like an air mattress) to fit on the top of the truck cap under the camper bed area to fill the space that exacts there - but I don't thing they make those anymore.

Has this happened to anyone else and if so how did you stop it?

Also, I tried changing my signature profile under my name but it won't take for some reason.

[pjay9]

WOW!!! This is fun to watch...never had the issue with 3 TC on 3 trucks...I bet some of the low cost solutions will work...less air in Bags, sounds good to me get some Stabiloads and make sure tires are at correct pressure...simple, hope these fix it! Tire/wheel is size expensive solution, but you may want them for other reasons down the road.

Waiting to see what works!!!! GOOD LUCK!!!

[whizbang]

Hmmmmmmmm.

Our porpoising improved when we switched to the 19.5 tires.

[stufarmer]

in 2005 I had a Ram 2500 swb & lance 861 Towing 21' Reagal Bowrider. Helwig Rear Sway Bar, Rancho 9000's. Airlift Bags and Super Springs. Also Toyo Open Country 10 ply tires. We traveled thousands of miles all over this country with ZERO problems. From my experience the entire center of gravity was everything.

[stevenal]

Timbrens will stiffen your suspension and reduce sag, much like Stable Loads will do. They provide no dampening.

[Jim_Carolyn]

Thanks to everyone for all your suggestions. I have already done a couple of the things suggested here.

While I was working on the camper today, a guy pulled up and started talking to me about his TC. As we got talking, I told him about the porpoising and he told me to get a Timbren suspension system and that will take out the movement. They are basically just some thick, hard rubber bumper pads. They look cheap and easy to install so I think I give them a try.

[dadwolf2]

IMO, GM OEM shocks aren't the best. From past experience I've noticed that if I have too much air in my bags the handling gets weird. If you have an onboard compressor / controller I highly recommend testing out different pressures, lowering the pressure so the weight is in the leaf springs helped me. I really don't think the problem is air lifting up the front cabover section.

[T3PAIR]

I have a 2014 AF 811S as well but on a Ford F350 . Similar set-up as OP. When I bought the camper, I brought along a tape measure and used the airbags to restore the truck bed height to where it was pre-camper without paying attention to the springs. As such, I had the bouncing issue you are talking about because all the weight was on the airbags only. They aren't designed to carry all the weight but are supposed to help your overload springs and level your load. I'd lower the airbag pressure if I were you. No need to put max pressure in it. When I get ready for a trip, I don't inflate to a specific PSI for each bag. Instead, I inflate past the point I need, but then slowly de-flate the bags until I see the overload spring engage with the rubber stops about an inch on the front and back. This allows the airbags to work with the springs, not independent of them, and allows the springs to do what they are designed to do. Has nothing to do with COG and I still have my original shocks too. The nice people at Les Schwab tires (when I got my 19.5's) taught me this, as I never would have figured it out otherwise.

[mooring_product]

billtex wrote:

mooring product wrote:


Its a short bed issue. You can slow it down but never stop it completely.

I don't understand this?

The relationship of a SB camper to SB truck is the same as a LB camper to LB truck.

Why would a SB on SB truck induce porpoising?

Please explain...

Tx, Bill

The space between the rear tire and the front of the bed is greater on a long bed truck. In a short bed truck with a large camper like your 811S and my 881MAX most of the weight is over the rear tires and not over the front tires. Teeter tooter affect

This is why many people say adding water helps because you put more weight in the front of the camp/in front of the truck.

[Bedlam]

I never had issues with with porpoising on my F250 extra cab with short short bed while carrying The Arctic Fox 811 (even when everything was stock on the truck). I addressed sag with upper and lower StableLoads. After upgrading to 19.5" wheels, I also added adjustable Rancho shocks to help control the heavier unsprung weight. Between the stock equipment and items added above, I had a great setup with minimal side sway and no noticeable rocking fore or aft.

I did add airbags to haul a heavy trailer this setup (also the reason for 19.5's), but I kept 50 PSI or less in the bags even when loaded at 8000 lbs on the rear axle.

Your porpoising is either caused by soft springs or light shocks. Pretension the springs with StableLoads or add additional spring capacity first. If your suspension still cycles multiple times over bumps, upgrade your shocks to ones with heavier dampening.

[magic43]

Springs and airbags do not stop movement. That is what shocks do. Bilsteins should work, but I installed Rancho adjustable shocks.

[billtex]

mooring product wrote:


Its a short bed issue. You can slow it down but never stop it completely.

I don't understand this?

The relationship of a SB camper to SB truck is the same as a LB camper to LB truck.

Why would a SB on SB truck induce porpoising?

Please explain...

Tx, Bill

[COboondocker]

Don't think it's a CoG issue. Had this same issue w/ our long bed 1 ton truck when the air bags were overinflated by the dealer. Brought the pressure down so the truck is level and the overload springs were engaged w/ the upper stable loads. Solved the problem. We settled on about 35 lbs in the air bags.

[mooring_product]

What I found that helped was stiffer shocks in the front and less air in the rear.Stable loads are a must to keep air pressure down. Stay away from Timbrens, they will make it much worse in my opinion.

Also keeping water in the tank helps.

Its a short bed issue. You can slow it down but never stop it completely.

[billtex]

romore wrote:
The camper is too long for a standard bed truck, too much weight behind the rear axle. The only way to fix it is to move the center of gravity forward.

Nonsenese...this is a SB camper...made for a SB truck.

The OP has too much air in the bags...lower the psi. Leave the overload springs engaged. You may only end up with 10 psi or so...
You will heave to expirement.
You'll be fine with the 1 ton.

Nice seup!

Bill

[Ski_Pro_3]

Do yourself a favor and listen to people that have had this problem. I too came home from the dealer with the same problem. I solved my problem with my short bed 4x4 dodge diesel with a Lance 855S using the Lance struts that are available from Lance.

They are not cheap and I can't say they will work in your case, but for me, they worked.