Front end bounces horribly when going over 55 mph

[tbchristian3]

Hello everyone, 

I have gone through most of the posts for cab over bouncing and I can't seem to find a solution that fits my current set up. 

I have a 2015 GMC Sierra 1500 5.3 L V8 4X4 Crew Cab.

The slide in camper is a sun lite pop up but I am not sure of the model number or exact weight. Unfortunately the guy I bought it from didn't have any info on it. He said he though it weighed roughly 1000 lbs. 

What I do know is the camper only sticks out a few inches past the tail gate so it's roughly 6ft long inside the bed. My bed is the 5.5 ft (the shortest bed they have in a 1500). I have the Happijac camper tie downs installed in between the cab and bed and tie downs mounted to the back bumper. I used a regular set of turnbuckles off of amazon. They are Brophy Machine Works brand and have a tensile strength of 2100 lbs.

The issue I am having is that when I get up to 55 mph or higher the front end of my truck starts to bounces uncontrollably. I have tried adjusting tire pressure and tightening the turnbuckles but neither of those things helped at all.  Any other pointers? is the camper to heavy for my truck? Is it a WD problem?

Here's a pic:

[Grit_dog · Accepted solution]

Not likely the issue at all. 
I feel like I asked a couple few questions you haven’t answered. As have others. 
what’s under it for suspension?

what you got for tires and pressure?

what kind of road, asphalt or concrete?

how long how far how many roads and miles have you driven it? Or any other heavily loaded truck?

I can get an almost empty truck bouncing pretty good at the right speed on the wrong concrete highway. Yet never had even a severely overloaded pickup bounce like that on smooth asphalt. Concrete panels create ridges at each panel joint where they’re saw cut, when the edges swell or curl. Sounds like what you’re experiencing, but until you provide more insight, can’t tell. 

[mkirsch · Accepted solution]

Concrete panels as in the road surface. Many highways are poured concrete, which have an expansion joint, or a cut line, at regular intervals to control cracking and expansion.

These regularly-spaced seams in the concrete can set up a harmonic bouncing in your vehicle at certain speeds and/or weights. Asphalt over concrete will do the same thing because the seams are still there under the asphalt.

Now that you know what to look for you can seek out a smooth paved road that isn't asphalt over concrete, where you can go 55 or faster, to see if it's the truck or the road.

You don't have to be overweight or dangerously light on the front of the truck to have this problem. You just have to be balanced wrong. Hence why I still think it's a weight transfer issue. In a nutshell: The weight of the 1000lb+ camper sitting at 2-3' behind the axle has lifted just enough weight off the front of the truck to make it sensitive to road seams...

One other thing that I don't think we've touched on: Is the bouncing uncontrollable or is the truck uncontrollable? 

[tbchristian3]

Thank you so much for all your advice, I was able to sell it for a profit. I think the next thing I will get is either one of the brand new super like cab over campers make for the light weight trucks (since my bed is so short and axle is so far forward) or just give in a get a bumper pull again. I am still looking at replacing the shocks because I think it needs to be done.

[MNtundraRet]

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@tbchristian3 wrote:

Thank you so much for all your advice, I was able to sell it for a profit. I think the next thing I will get is either one of the brand new super like cab over campers make for the light weight trucks (since my bed is so short and axle is so far forward) or just give in a get a bumper pull again. I am still looking at replacing the shocks because I think it needs to be done.

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You made the right choice. Getting the right pickup to hall your topper was the correct route to go. There were no good options, cost wise, to modify the other pickup. 

[joerg68]

What you describe would be consistent with a "light" front axle. Your truck and camper are good candidates for that. Before you investigate any further, go to a Cat scale and get the individual axles weighed.

1000 lbs sounds very, very light for a camper ready for travel.

ETA: in any case you will be near or over the truck's payload and / or RAWR. Which does never improve handling. Is the bounce that you describe more of a porpoising motion?

[joerg68]

It is possible that the camper exceeds the payload of your truck, and that the camper CoG is far enough back that it even transfers weight from the front axle to the rear. That would explain your handling issues. 

Get the truck axles weighed with and without the camper in the bed. Then compare the actual weights with the FAWR/RAWR as stated on the door sticker of your truck, as well as the weights of the axles without camper and with camper.

If nothing else, you will know the actual weights of the truck and camper.

[tbchristian3]

Any idea on where I can weigh it? I have no clue lol. It seemed to handle fine until at 55 mph but I was also to afraid to go any faster than that with the bounce and there being no bumps to cause it. Could it also be wind pull on the camper in between the top of the cab?

Payload sticker says 1595 total.

[RickW]

First, go to a truck stop with a weight scale.  Weigh both axles of the empty truck (full gas tank).  Then mount the camper and weigh again.  I expect the weight on the front axle to decrease with the camper having the center of gravity behind the rear axle.  This will make your truck drive like a see saw rotating on the rear axle.

Second, verify your tire type and pressure.  1500 trucks are delivered with passenger tires that are too soft for heavy loads.  You need LT tires, preferably load range E that can be pumped up to a higher pressure when carrying the TC.

Third, look into stiffer shocks to dampen the springs.  Some of us use adjustable Rancho 9000s so the empty truck doesn't drive like, well, a truck.  If the truck is squatting when loaded, look into timbrens or other spring stiffeners.

If still too bouncy, brakes poorly or rolls on turns, get a larger truck, or lighter camper, or start over..

Hope this helps,