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Old 11-09-2013, 08:16 PM   #1
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What is chucking? I have a problem with my 5th wheeler bouncing on city streets. Feels like the truck and trailer get into some kind of oscilation and it feels like my truck will bounce off of the street. Any info to help?

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Old 11-10-2013, 09:20 AM   #2
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Originally Posted by danbarnes194 View Post
What is chucking? I have a problem with my 5th wheeler bouncing on city streets. Feels like the truck and trailer get into some kind of oscilation and it feels like my truck will bounce off of the street. Any info to help?
To soft springs and shock absorbers not doing their job. Might be the pin load also to light for weight of trailer. Very dangerous.

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Old 11-10-2013, 09:59 AM   #3
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You don't provide much information to help folks answer your question. What TV do you have? What 5th wheel are you pulling? What is the pin weight, trailer weight, what kind of hitch are you using, what suspension mods, if any? If you can provide some info, I'm sure someone can help you....
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Old 11-10-2013, 08:29 PM   #4
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Chucking is a physical phenomena, when you have uncoupled entities exerting unequal forces upon each other. The fact that you have a hitch in between means nothing, the truck and the trailer are two different entities held together by the hitch. Here's where the "fun" begins. You typical pickup will weigh between 6-8,000 pounds, an equal weight fifth these days is an entryway clunker, most better fifths you'll see are around 12K and they go up from there (sky's the limit). You hitch up 16-18K fifth behind that pickup and you have 2-3 times weight differential coming into that pickup and acting on the truck's rear suspension (through the hitch pin). Second, the fifth typically has much longer wheel base compared to the truck so it responds to motion differently. Thirdly, the brakes on the fifth are nor coupled directly to the truck brakes, you can fiddle with the controller to try to match them (in response time) but you can come close only at certain speed and certain brake pressure, the minute you increase (or decrease) the speed from the set point the adjustment goes out the window, the minute you put the hammer down hard, the adjustment goes out the window. Which means there will be typically a time lag before the brakes on the fifth start reducing the force vector pushing the truck. If you set the fifth's brakes on the aggressive side you will get the opposite, a jerk back.
We instrumented a hitch pin few years ago with a strain gauge,

to see what kind of forces we could see on the pin, the fifth and the truck during pulling, starting and stopping. There is a lot of weird stuff going on there and there is anywhere from two to three (or more) up and down and forward and back cycles before things settle down after any "disturbance", going over dip, pothole, braking or even just getting off the gas.
The bigger the truck/trailer weight differential the bigger the chucking problem. HDTs exhibit the least amount of chucking, even with big fifths

for two reasons. Typical HDT will weigh more or close to the fifth it pulls (even the "big ones") and second typical HDT conversion places the hitch behind the rear axle.

Which means that whatever motion is generated between the fifth and the truck gets dissipated behind the rear axle and into the rear axle, very little of it transitions forward into the cab area.

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Old 11-13-2013, 08:24 PM   #5
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The first item to check is the truck shocks. OEM shocks last about 25,000 miles of ordinary driving, towing a trailer cuts that severely. The pin weight of your 5er should be 18-25%, depending on mfgrs design.
When you replace shocks, several have lifetime warranties, Rancho, Bilstein, and several other brands. I bought Rancho shocks from Sears and installation. They have replaced them 2X now in 84,000 miles at no charge. I used to tow a 15,500# 5er with my dually, and it was obvious when the shock were failing. I would get chucking and the truck would bounce more than 2X when driving over potholes.
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