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.

[wcjeep]

Run with full fresh, empty grey/black. This will help tremendously.

If necessary lower the airbag pressure and install Torklift Stableloads.

[jmtandem]

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.

Porposing has absolutely nothing to do with air under the camper nose. Get some real help from those that know better. Your COG is too far back and it is causing the truck when hitting a bump to set up an oscillation.

[MORSNOW]

I would install Upper and Lower Torklift StableLoads to get the load back on the rear suspension and off of those airbags. The airbags are not helping you with the porpoising, they may be adding to it. Let your shocks and springs work as intended and just use the airbags for side to side leveling.

[AISURFFISH]

I noticed it when I had my 881 max on the short bed truck too.. but I can say it does not happen as much as our new long bed set up and camper. Maybe it's a wheel base thing....

[jimh406]

I'm not why people are jumping on the COG bandwagon so quickly. I have a couple of things to try that don't cost money. Porpoisoning is an out of balance condition front to rear. The fact that the rear is bouncing when the air pressure is lower implies the shocks are too weak but lower tire pressure can create a similar affect.

Increase the tire pressure in the front and rear. I suggest bringing the pressure to maximum which is probably 80. Lower the air pressure in the rear until the truck is riding level.

Those changes should help. Other things that many people have done that does help with bouncing is switching Rancho adjustable shocks.

You can also add Torklift stableloads or fashion your own extended bump stop stops to ensure the rear overloads are always engaged with a load. I don't know if those apply to your truck.

[sabconsulting]

I can get that 'porpoising' sometimes on certain road surfaces for a short period. I believe my camper's centre of gravity is slightly behind the rear axle of my truck, which isn't ideal. I suspect the more its CoG is behind the axle the worse this is. An 811 has a 9ft floor doesn't it? Is there any indication where along its length the CoG is supposed to be and if so where is that in relation to your rear axle?

I doubt it has anything to do with air getting underneath - more the road surface, especially if a concrete freeway which is poured in sections.

In my case I think changing the front dampers helped a bit, but the existing ones had 60,000 miles on them so were pretty tired.

Also, I find the pressure in the air bags makes a difference. I run mine at low pressure; too much pressure and I find instead of the rear suspension flexing and absorbing the bumps, it just passes them onto the camper resulting in a more choppy ride resulting in more porpoising.

Steve.

[tonymull]

Yep center of gravity problem. Consider where your water tank is, run empty or full according to where it is, move as much weight forward of the rear wheels as you can. Is the 811S built for short beds?? (The guy at the dealer, by the way, is full of it)

[romore]

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.