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Old 08-31-2009, 07:30 PM   #1
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How to stop rear axle bounce

I have a 06 2500 HD Chevy Duramax short bed crew cab. My rear truck axle bounces excessively on bumps, such as highway bridge abutments, when pulling my 2,800 pound pin weight fifth wheel. The parts manager at the local trailer dealer told me that he has had a number of customers with Chevys who complained of the same problem, and they cured that problem with new stiffer shocks. Does anyone have any experience on this issue? I am tempted to put on new shocks but want to make sure it is the best fix for the problem before I proceed. Another more costly option would be an air pinbox. If anyone has successfully cured this problem with new shocks, which shocks should I get? Like any idiot who wants to have his cake and eat it too, I would of course like to cure the problem without have a rock hard ride when unloaded. I have been told that Bilsteins should work, but will result in an extremely rough ride unloaded. Anyone have experience with other shocks?
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Old 09-01-2009, 08:04 AM   #2
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OEM shocks are designed for ride mainly, with a lifespan of about 20K miles of "normal" use. Look at Bilstein shocks, Rancho 9000 shocks; they both have a lifetime warranty, and the important thing_great control of a loaded truck! They do wear-out, mine have been replaced once (Sears-no charge) since 05 and are nearing it again.
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Old 09-01-2009, 09:46 AM   #3
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I would strongly suggest that before you go out and put band aids on the problem that you load up and make a trip to the scales. From personal experience I am willing to bet that you are way over the manufacturers GVWR for that truck. The only real cure for your problem is more truck.
Next is air bags and new shocks along with higher rated tires and wheels.
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Old 09-02-2009, 01:48 AM   #4
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Donn, not only do you have the same name as my father, you sound like him. (-: Yes, I have been over the scales, and yes I know I am over the vehicle's GVWR of 9,200. But with a truck weight (with wife, fuel, and hitch) of 7,500, I would be limited to the smallest and lightest of fifth wheels if I attempted to stay under the GVWR. Considering just pin weight (1,700 pin weight added to my truck gets me to the GVWR of 9200), my 2500 HD should not be hauling any Challenger, Montana, and a multitude of other medium weight fifth wheels that all have pin weights exceeding 1700. If all the 2500 Chevy users stuck to the GVWR, 90% of them would have to get much lighter trailers.

If shocks are bandaids, you might want to consider taking yours off your truck and see how well it handles.

I am under the GAWR both front and rear, under the GCWR, and under the maximum fifth wheel hitch weight recommended by the manufacturer. My last fifth wheel had the same pinweight as this one and I had no noticable bounce. My guess is my current bounce problem has more to do with the aging of the OEM shocks (40k miles on them), and the balance of the new, heavier fiver. I am also guessing that that the parts manager at the local trailer dealer was being honest with me (since he doesn't sell shocks) when he told me that he had talked to close to 20 customers with GM trucks over the years who had a similar problem due to the soft OEM shocks used by GM, and 80% of them cured the problem with new, firmer shocks.

Oh, and I already have airbags and higher rated tires.

I just want some feedback on which shocks I should consider.
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Old 09-02-2009, 10:30 AM   #5
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Thanks for the come back.
I was not talking out of my hat. I have been there and done that. It does not change the ride characteristics no matter what you do.
My 2500HD D/A scaled ready to camp at 7500 pounds and hitched to my fiver it was 10,500 pounds. So I am speaking from experience. The fiver scaled 10,350. There is nothing you can do that will make the ride better.
But since you are interested in shocks, Blistenes are probably the ones most people recommend first.
Go for it!
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Old 09-02-2009, 10:45 AM   #6
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Donn, I appreciate the discussion. Your setup you just described is very similar to my first setup. The trailer had a pin weight loaded of 2800 and a loaded trailer weight of about 10,500. You had bounce, I had none. Now I have bounce with the new trailer at a similar pin weight but an overall heavier trailer. Now I am starting to guess, but I am thinking that with the new trailer being heavier, but with a similar pin weight, the rear end must have more weight which results in a teeter-tauter (see/saw) harmonic effect. Ray recommended Bilsteins or Rancho 9000's. I have researched the Ranchos (I like the idea of adjustability) and found some users who reported a problem similar to mind that was fixed nicely with the installation of Ranchos. I think that is the way I am going to go. I will post the results.
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Old 09-02-2009, 10:49 AM   #7
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Ray, thanks for the recommendation. I will probably go with the Ranchos. I researched them a bit after reading your response. Some users have reported correction of bounce problem with these shocks and I like the idea of adjustability. Too bad I have limited income (don't we all), or I would go with the onboard adjustability for both the shocks and my air bags. Boy, would that drive the wife crazy, with me making adjustments at every change of the highway.
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Old 09-05-2009, 03:18 AM   #8
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I got the Rancho 9000's installed today on my 06 Silverado 2500HD Crew Cab 4x4. Tried different settings for the unloaded truck ride. Settled on setting number 4. The lower settings are just too mooshy for me. Wife likes the ride. I then set the shocks at number 9 for maximum firmness, hooked up the fifth wheel, set the airbags at 50 psi to level the truck and fifth wheel, and headed for the scales. Combined weight was 21,750 (with nearly full tank of water), which is 250 shy of the GCWR according to Chevy. Now for the test ride. Took it down the highway to the highway bridge that got it bounding pretty good with the old shocks. It rode over the bridge very well. When I had gone over this bridge with the old shocks, the rig bounced and oscillated for what seemed eternity. Now it is a short bounce, a rebound, and then the shocks smooth it right out. So it seems the parts manager at the local trailer dealer was right. My worn out shocks were causing the bouncing/oscillating problem. These new Rancho 9000's have provided the cure.
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Old 09-06-2009, 03:34 PM   #9
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I have a 2500HD gas, same wheelbase, slightly lower weight because of the lighter powerplant. I have noticed mine tended to porpoise as well when towing a travel trailer (not a 5er). I installed new shocks, and found it helped, but did not totally eliminate the issue.
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Old 09-25-2009, 12:01 PM   #10
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Okay, I know this is a bit of an old post, but I can’t help commenting.

As Don said, I am speaking from experience. I have been there and done that as well. I agree with Don completely. You are throwing band-aids at a very common problem. You have too much fifth wheel for your truck. And I will admit I have been guilty of all the same justifications and rationalizations that other ton truck owners like you use to convince themselves they aren’t putting way too much weight behind them to be safe.

GCWR is not a legal weight rating. You will never find GCWR on your weight stickers. You might see it in your manual or on a website, but it is only in the literature. GCWR and max trailer ratings are simply recommendations that are thrown out there more for marketing purposes than anything else.

GVWR and AWR are the only ratings that matter. These are legally enforceable ratings, even if it is very rarely enforced. These ratings are not to inconvenience you, and they are set for overall truck capacity based on safety testing of the entire package. Adding airbags, or other load helpers does absolutely nothing to make it safe to exceed these ratings. You have no idea what single component of the entire truck was the limiting factor in testing these limits. It might be the steering or the brakes. Consider that your truck has to be capable of stopping the load behind it within a safe distance in the event that the trailer brakes fail. And you have to be able to steer and maneuver safely in an emergency situation with all that weight shoving your truck around by the rear axle. Adding airbags does nothing for increasing these capacities. It is a comfort improvement only.

Simple math makes me wonder about some of your numbers. You claim your last fifth wheel had a loaded weight of 10,500 but a pin eight of 2,800. That’s a 27% pin weight to trailer weight ratio. That’s extremely high, by far the highest I have ever seen. If you were truly at this pin weight, I suspect you were underestimating the loaded weight of your trailer. Having shopped extensively for new fifth wheels last year, I can say that the literature on most fivers out there show a pin weight ratio between 17% and 23%, with Toy Haulers having the heaviest dry pin weight ratio. All of my fivers have had actual pin weight ratios within this range, and except for our Toy Hauler, all were under 20%.

You say your new fiver has a pin weight of 2,800 lbs. But since your truck weighs 7,500 fully loaded (“wife included”), and your total weight was 21,750, that means your trailer weighed 14,250. That’s a pretty heavy fiver. But your pin weight ratio here is much more believable at 19.6% of the trailer weight. Here is where it gets fuzzy. You new fiver weighs 3,750 more than the last one, or an increase of 36%, but your pin weight is unchanged. That just doesn’t add up. You gained almost two tons and the pin weight is unchanged. Again, I strongly suspect you were either overestimating the pin weight of your previous fiver and underestimating its total weight. Most likely it was the pin weight. And that makes sense, because if the pin weight didn’t change, why did you feel a sudden and major change in ride from one fiver to the next?

My last truck was a 2001 Ram 2500 Cummins short bed. My setup allowed a max pin weight of about 1,600 to 1,800 depending on the load in the truck. My last fiver weighed between 10,500 and 11,000 loaded and the pin weight was right at 1,800 lbs. At the scales, this combo was 200 lbs. over my GVWR for my truck. I was well under my RAWR because my RAWR was 6,800 lbs.; I had the Dana 80 1 ton axle in my rare drivetrain combination. (But your RAWR is only 6,084 lbs.) My total weight was almost exactly 18,000 lbs. But according to Dodge, I was within the theoretical GCWR of 20K lbs. for that truck.

We lost that fiver in an EF4 tornado last year. It was parked in our driveway. (See the pics in my gallery and you can see the fiver on its side right after the storm.) We went out last fall shopping for a toy hauler. I knew we would be overweight, but I thought we would get by for a year. Wrong. The truck pulled it like a dream. But the truth is it was still too much trailer for our truck. And the pin weight was 1K lbs. over our GVWR. That truck is long gone and I now have a 3500 DRW – an appropriate truck for that trailer.

No matter how you slice it, you are at least 1,000 lbs. over your GVWR, and I suspect you are well over your RAWR. Just curious, but how many axles does your fiver have? Anything that weighs in over 14K lbs. should have 3 axles. Any triple axle fiver is too big for any shortbed ton on the road. They simply don’t make a 3/4 rated for that much trailer. Just because you can do something doesn’t mean you should, and definitely doesn’t mean it is safe.
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Old 09-25-2009, 12:13 PM   #11
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Quote:
Originally Posted by thecatsfan View Post
GCWR is not a legal weight rating. You will never find GCWR on your weight stickers. You might see it in your manual or on a website, but it is only in the literature. GCWR and max trailer ratings are simply recommendations that are thrown out there more for marketing purposes than anything else.
From the Texas Transportation Code:

Quote:

Sec. 522.003. DEFINITIONS. In this chapter:

(17) "Gross combination weight rating" means the value specified by the manufacturer as the loaded weight of a combination or articulated vehicle or, if the manufacturer has not specified a value, the sum of the gross vehicle weight rating of the power unit and the total weight of the towed unit or units and any load on a towed unit.

(18) "Gross vehicle weight rating" means the value specified by the manufacturer as the loaded weight of a single vehicle.
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Old 09-25-2009, 01:29 PM   #12
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good points all around.....

fact is unless you have a very light 5er you are going to be over some number if u tow with a 3/4ton, or even a single wheel 1 ton for that matter.

on another note....

I would like to know why a dodge quad cab dually has 2K more on its GVW vs a mega.
i have a 06 mega DRW and a friend has a 06 quad DRW his GVW is 12,500 mine is 10,500....... what maks such a diff that the quad gets and extra 2,000 lbs???

another funny number is some 3500 mega cab SRW have GVW of 10,100 and mega cab DRW have 10,500??? what the heck only 400 lbs extra for DRW?? after u add in the weight of the 2 extra wheels, tires, and fenders u gain nothing...makes no sense at all to me.
The mega DRW is grossly under rated i think.
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Old 09-25-2009, 01:40 PM   #13
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From the Texas Transportation Code: Sec. 522.003. DEFINITIONS. In this chapter:

(17) "Gross combination weight rating" means the value specified by the manufacturer as the loaded weight of a combination or articulated vehicle or, if the manufacturer has not specified a value, the sum of the gross vehicle weight rating of the power unit and the total weight of the towed unit or units and any load on a towed unit.

(18) "Gross vehicle weight rating" means the value specified by the manufacturer as the loaded weight of a single vehicle.



Rusty
Notice the part in section 17: "if the manufacturer has not specified a value"? That's in the code because on personal use vehicles, GCWR is not specified. It isn't a valid enforceable rating. Dodge, Ford, Chevy - none of them put GCWR on the vehicle weight tags - not even for vehicles sold in Texas. Number on their website or in their manual are marketing recommendations only. Those GCWR numbers are not a valid weight rating and cannot be enforced.

Section 17 goes on to state that if unspecified GCWR includes "the sum of the gross vehicle weight rating of the power unit and the total weight of the towed unit or units and any load on a towed unit." DUH! all that says is if you add the weight of the truck and the weight of your trailer, that is your total weight. DUG AGAIN! But what does it mean? Not much.

You took this information completely out of context as well. If you read the entire section 522.003, you would see that the only time they use this information is to determine if a vehicle is classified as commercial or not. Most states consider any vehicle with a GVWR of over 26,001 lbs. or a GCWR of over 26,001 with a towed trailer with GVWR of over 10,000 lbs. as a commercial vehicle.

And you neglected to point out that even in Texas, unless the vehicle has a GCWR over 26,001 lbs. specifically marked on the weight tag, or the vehicle has air brakes, or you are registered with DOT and driving commercially, this rating does not apply and is completely meaningless.

For the sake of the original discussion, only including the vehicles discussed in this thread, I completely stand by the statement that "GCWR is not a legal weight rating" and that it is not an enforceable weight rating on these rigs.

If you are driving a Chevy 3/4 ton and you weigh 21,750 GCW, but your GCWR in the owners manual was only 20,000 lbs., you cannot be ticketed for exceeding that limit, as it os not a legally specified weight limit and is completely unenforceable.

Yes, if you get up to 26,000 lbs. total weight, in some states then they might give you a hard time, but below that weight, they can only ticket you for exceeding GVWR or either AWR. Once you register with DOT and begin driving commerically, other limits may be applicable.
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Old 09-25-2009, 01:55 PM   #14
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This definition, although located in the CDL section, is referenced in many places throughout the Texas Transportation Code. For instance:

Quote:
Sec. 521.001. DEFINITIONS. (a) In this chapter:

(4) "Gross combination weight rating" has the meaning assigned by Section 522.003.

(5) "Gross vehicle weight rating" has the meaning assigned by Section 522.003.
My truck manufacturer has defined a GCWR, so the alternate definition doesn't apply. Just because it isn't on the driver's door sticker doesn't mean it doesn't exist. I actually carry a copy of the page from the owner's manual defining the GCWR in the console along with my insurance cards.

My point in quoting the Texas Transportation Code is that some states have indeed codified the manufacturer-defined GCWR, so to state in absolute terms that it isn't a "legal weight rating" may not be such a good idea.

I'm actually in agreement with you that 3/4 ton truck owners shouldn't merely look at GCWR or "manufacturer's trailer tow rating", but instead should read the fine print in the manufacturer's towing guides that generally states that "none of the truck's other ratings should be exceeded" - which means GVWR and GAWRs, and there are far too many SRW trucks towing large 5th wheels that are well over the trucks' GVWRs.

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