I have seen a few discussions on this and have done a search, but could not find the info I wanted so here goes.....

At exactly 43mph(according to properly calculated Juice W/A), the rear of the truck starts to bounce up and down about 2 inches each way. This bouncing stops by 46mph and never happens at any other speed. It does not seem to be engine rpm related since I have let off throttle and let rpm's drop and vibration remains until about 41mph then it stops. Tires have been balanced 3 times, but no help. Any load in the bed of truck and vibration will tend to disappear, but I still notice it to a small degree unless it is a somewhat heavy load.

I have cranked the T-bars to level out the truck. Could this be the source of the problem? If not, what could it be

Subject: Suspension Vibration or Frame Beaming at 40-60 MPH - keywords chuggle rear shake shock spring TCC tire #PIT3009C - (06/28/2006)



Models: 1999-2007 Chevrolet Silverado Classic

1999-2007 GMC Sierra Classic




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This PI is being updated to add 2007 model and to advise that no more FPR are needed. Please discard PIT3009B.


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The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
Beam shake vibration is usually felt in the seat and occurring between 40-50 mph. Hertz readings using an EVA tool are normally between 8-24 Hz. This condition is most common on extended cab and crew cab models but has also been noted in other models.

Recommendation/Instructions:
The severity of beam shake may vary from vehicle to vehicle. To determine if the concern is beam shake, please perform the following:

Test drive vehicle to confirm the condition. A beam shake condition will usually respond to concrete type pavements more than asphalt, so the vehicle should be driven over both surfaces if possible.
Place 200-500 pounds in the pickup bed between the closed tailgate and the wheel wells. A beaming condition should dissipate.
If the concern is determined to be beam shake, this is a characteristic of the vehicle and currently no repair attempts should be made. With your help in the use of the Field Product Reporting process GM Engineering is currently developing a enhancement to the body mounts to reduce this concern on the 1500 Models and should be available shortly. There will be no enhancement made to the 2500 and 3500 models. At this point no more Field Product Reports are needed and Thanks for your help.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

Good answer, Ben..I was going to ask if he had dogs humping in the back of the truck....):h

Thanks fellow Honda fanatic!

Well I guess it sounds like I just need to get use to the feeling of two dogs humping in the back if I am going 43mph):h

Or just load 200-500lbs of dog food in there with them!

If you tune the dog humping frequency to counteract the frame beaming, GM just might include the fix on all the trucks:)

redrider,

mine does the same exact thing and has since I bought it. I had it to the dealer a number of times but they never could fix it. I wish there was a correction for this but I have been learning to get used to it. Mine seems to do it around 42 mph and goes away by 47 mph.

There is a fix to this issue that GM does not want to admit to. The addition of a rear sway bar corrects this issue. This is accomplished by tying the rear axle to the frame via an articulating sway bar and endlinks that supports and stabilizes the housing unit by means other than spring tension (via rear leaf springs).

The sway bars were not invented to correct this specific issue but are a welcome “side affect”.

Tom,

Is there a kit available from the dealer or aftermarket that you know of? I was wondering if you can elaborate a little on this fix. I am definitely interested in taking care of this problem and would appreciate any additional information you can supply. Thanks.

If you look at this photo then call me it would be easier for me to explain.

http://members.cox.net/movitusa/GMHD02.jpg

Who makes that sway bar kit? Mine shakes as mentioned but not 2" each way and it tends to be more in the 50mph range. I have grown to adjust my speed or just deal with it. It is frustrating though and I would entertain the thought of a sway bar if there is a reasonably good chance of reducing the shake and at a good price.

Thanks for the heads up.

Tom -
Can you comment on this quote in another thread? Based on your comments in this thread it seems contrary.

"The shudder or bounce in the stock rear suspension is more pronounced with the sway bar package installed but, I think this will be solved with the change to Bilstein shocks." - Anethesia

I too have this bounce and it is annoying. While I don't entirely discount the beam shake issue, I feel this is something new that came on after 30k or so miles. While the beam vibration story implies that it is inherent in the truck design, that has not been my experience. I have replaced the shocks with Bilsteins (from Kennedy) and it was better but not gone. My next check will probably be the U joints, but if this is characteristic of these trucks as they age (although I feel 50k miles is young), I would consider your sway bars to resolve it. It wouldn't be entirely disappointing to have my 2500hd handle more like the Mercedes E430 it replaced.;)

Holy cow - I think this is the condition that I have been attributing to my cranked t-bars. I was going to invest in a 4" lift to correct this but I might as well try the sway bar first.

Mine starts shaking/bouncing at about 47-55 mph. Does not do it at any other speeds. Did not do it until I cranked my t-bars - they are only slightly cranked just enough to get my 285s to clear.

So - reading the above - it seems that a rear sway bar might induce this condition?

My '02 has the vibration since day one, starts about 42 mph and ends about 47mph. Installed Bilsteins from Kennedy, and that didn't fix. Would be great if there was something out there to fix. Keep posting on something new.. Thanks...

I have the same exact problem on my truck. 2001 GMC Sierra 2500HD 4x4 Crew Cab 8100. Right about 42-45mph the rear of the truck starts bouncing up and down. It did it before and after I cranked the front up. I've replaced the tires and shocks, still same problem. I would be REAL interested if the addition of a rear sway bar would cure the problem.

Exactly-that's what mine's doing. Only aroung the 45 mph range is when it bounces-you really feel it in the seat-very annoying. I would spring for the sway bar if it corrected the problem.

Mine too!! I thought it was becasue of cranking by T-bars.

It was doing it around 45mph with the rear tires at 80 psi. When I lowered their pressure to 50 psi it starts the vibration at 50 mph! ???????

I have some Bilstiens on order....was hoping that would correct it. I might go ahead and cancel the order....it has been almost 2 months on backorder anyway!!!

I guess I got lucky as a set of Bilsteins took ~90% of mine out which was enough to satisfy me.

s

http://www.dieselplace.com/forum/showthread.php?t=92485&page=1

http://www.dieselplace.com/forum/showthread.php?t=92267

Lots of answers there.

Unforunately not the one this thread is looking for. Sorry but trying to get this back up.

My point is that there is a claim that the sway bar is reported to fix this problem.

LTChip - I agree 100% with you and that post was just to try to see the thread continue. Thanks for posting that info and trying to keep this going. I just don't want this thread to die without some more discussion of whether that is the case. Because one other thread contradicted what Tom said by saying it got worse, but I would like to give both Tom and some of his other customers a chance to support this as a solution to this problem. From the months of research I have done, many people experience some form of this problem. Hopefully this thread can showcase a solution from a small independent vendor that the big guys couldn't or wouldn't solve. Unfortunately GM has determined this to be the frame design problem as mentioned earlier in this thread, and therefore given up on it.

As an aside, if I had the money right now to spend on Tom's bars, I would consider calling him personally to find out, but don't want to waste his time(which must be at a premium due to the deal he is provding). I am hoping to strike while the iron is hot to determine if his other customers have found these to solve this problem.

I will try to address this issue as best as I can by writing it out. I really stink at writing technical answers like this question needs. It is like my brain is not attached as well to my hands as it is to my mouth. Nor do I have a Purdue Engineering degree, just real life street trial and error engineering experience. It is also hard to describe with out diagrams which I do not have.J

Short Version:
The rear end is twisting for lack of support while driving and causing the rear to harmonically “bounce”. Traction bars address this issue as well as sway bars will but sway bars stop the swaying of the truck at the same time. Traction bars do not help the sway issue.

Long version:
There are several forces at work here in regards to the “bounce” issue. First is the lack of lateral support with this differential and its connections to the frame. This truck has a lot of rear end torque. Torquing or twisting of the rear end. Anyone that has upgraded the rear end with torsion bars probably does not have this issue which is one fix. This is due to the rear end being “anchored” better than it is when stock. The stock rear “anchor” points allow the rear end to harmonically isolate at certain speeds due to the lack of fore and aft “anchor” points of the rear end and the having the “anchor” points attached only to the frame via the springs which multiply the harmonics of the rear end due to their flexible nature.

Did I lose anyone yet???

The leaf springs flex or “bounce” and the shocks are suppose to isolate or stop the springs when bouncing. The shocks stop/slow up and down isolations, but the shocks can not stop the rotating of the rear end front to rear when you are driving. It starts a harmonic circle. Albeit small, it is just enough to be noticeable and irritating and too small for the shocks to stop.

How do the sway bars stop this?

If you look at the photo of the rear end with the rear sway bar you see that the bars attach to the frame and the rear end at points that do not stop the torquing completely but offer more than enough resistance to slow the torquing of the rear end. This stops the previously uncontrolled fore and aft harmonics of the rear end and the bouncing stops. At the same time with the sway bars you are controlling the truck from rolling when cornering. Two benefits in one product.

If GM were to address this bouncing issue I believe it would be via the install of a rear sway bar and that would cost them a lot of money. To them it is a comfort issue not a safety issue. This explanation and statement is only my opinion. If I have confused anyone call me. It is easier for me to explain via verbal communication.

First of all Tom well done. I do understand your explanation and it makes sense that there is little attaching the axle to the frame other than springs and shocks. I guess this is why some feel that the initial rate of the springs are too soft. Any reasoning as to why one of your customers felt that the situation may have been amplified by your bars? Maybe it isolated the bad stock shocks once everything else was tightened up.

It's curious, I have the bounce in my 3500 DRW that starts around 41mph goes away around 50 and then returns around 62 and remains. I have had the wheels and driveshafts balanced with no change. I wonder if this would cure my problem. Good excuse to get something new for the truck anyway.

Tom - that is a great explaination and good enough for me. Will call you tomorrow.

Thanks.

Thanks Tom for the explanation. It really makes a lot of sense.

If there is anybody out there that had this 45-50 mph "bounce" and installed a sway bar that took care of this issue, I would love to hear from you. Before I fork out the dough for a sway bar I would like to make sure it corrects this problem.

I can use the sway bar anyway and I definately have "the hop" so I went ahead and ordered it.

Will get it installed within the week and report back if it helps the 40-50mph bounce.

Thanks LTChip, I will be interested to hear of the outcome.

I'm interested in the results also. Although the "hop" isn't as bad right now because I put my topper on for the winters. The extra weight seems to help.

I agree, some weight in the back seems to almost elimate the bounce. It sure is annoying though when it's empty.

LTChip did you get your new bars installed yet?

Not yet. Have not rcvd them as of yet. Tom said to give it three weeks and it has been about a week and a half.

Funny, mine used to bounce as well at about 45, I thought it was a wheel out of balance, recently built and installed rear dual shocks/hoops mainly for looks to match the front, the bounce has completely gone away, just an FYI...

Those look sweet!

Well, add me to the club :(. I recently noticed a vibration in the rear of my truck at 45 MPH. Just had my tires rotated and balanced but the vibration is still there. I am interested to see if the sway bar resolves this problem.

I usually have a 5th wheel hitch in the bed of my pickup and I still have the vibration. I guess the hitch weighs around 250 lbs. I'm fixin' to take the hitch out for a trip next week. I hope the vibration does not get worse.

Have a good day!

Bars came earlier in the week but I don't have them installed. Working on fixing the air leak in my fuel system first. Should an update on the bars by the end of next week.

Glad to hear you got them. Keep us posted!

LTChip, got an update on the bars?

Yes- the bars were put in about a week ago. The installer had to mod my exhaust to get them in and did a great job. He was very impressed with the handling difference in the truck once he got them in. Since then, I have driven the truck about everyday and probably logged over 1000 miles including some towing 4500lbs (200 miles approx). I have done city and highway driving at various speeds and various road surfaces.

I can say definitively that these bars are very effective at improving the handling of my truck. Towing and unloaded - the feeling you get with the bars is that the truck is more responsive and feels like a much shorter truck. Steering seems to be quicker and the rear end comes with you in lane changes much better than stock. Cornering is greatly improved with the truck staying nice and level and in control at speeds that would have made me a bit nervous in the past. The truck does not want to hop or drift when cornering as it did before. All of this is also noticeable when towing.

Now- as far as the bounce goes - I'd say that it is 90% gone since I installed the bars. If I am trying to feel it at the right speeds - I can still feel the bounce but it never is prominent enough to get my attention or that of my passengers. I would concur that the bars are a cure for the bounce.

To give you another perspective besides my SOTP – the bounce in my particular truck used to cause my GPS unit to bounce around in an almost violent fashion when I was in the 45-55mph range that produced the effect. (the unit is a hand held GPS in a car kit that I mounted in my ashtray so it is sort of cantilevered out from the dash making it a great bounce detector). The unit hardly moves at all under the same conditions now. I am very pleased.

Bottom line is that Tom’s bars come highly recommended from me. Probably the best $$ I spent on my truck from a value/performance per dollar spent perspective.

That is fantastic news!!


Sounds like this man just got some more business coming his way. I guess I'll have to add this to my Looooonnngggg list of things I want as well.


C-ya

Anyone here make their own rear sway bar? Looks very easy to make with a simple Mig setup. I wonder if the bars are made with one piece of steel and just bent with a hydrolic pipe/tube bender.

Thanks for the update LTChip. I appreciate your detailed feedback. Sounds like I'm gonna be getting me a set of bars here real soon. The bounce drives me crazy!

Tom- Very good job at both simplfying the issue and causal effect, plus a good photo. Nice work!

Another one of the 'joys' by cheapening/eliminating a rear sway control in a staggerd shock set up. Be careful don't give the makers too many solutions, you want to keep selling more, and they're helping you.

How about a computer simulation of the elliptical circle plus the fore/aft shake would be a great addition to your site, and puts a "word picture" that a viewer won't forget.
Heck, if going that far show a Hertz scale before and after your sway bar, with harmonic improvements to the gluteus maximus.
Bet you couldn't fill orders fast enough.

Had the issue, but designed/installed a solid bed cover of diamond T6061, beam bridged it, and tied it laterally at the four corners, vibration was history. BUTT, since I tow my equipment show trailers alot....I've wanted to add a sway bar to enhance handling. As a drop in....yours would be it if I don't get a true '07.

Have you seen the the GMT900 frame/suspension yet?
What are the dampening bushings made from?

Thanks.

Has anyone had their drive shafts balanced and foam packed?

LTChip - was wondering now that you have had the bars on your truck for a while now, have they definitely eliminated the bounce? Just curious. Thanks.

bump

I have it and have spent tons of money trying to isolate it.. I have new tires, new rims, new Kennedy shocks and drive shafts(front and rear) dynamic balanced. The dealer, God bless him, replaced a rear rotor, and hub that were out of spec. No worky.. Then, they took the driveshaft out, took the axles out and drove it with front driving to eliminate the driveshaft, axles and pinion.. Still hopped. The only solution they came to was taking my 285 tires off and running a set of stock tires and rims from a new Duracrap on the lot. The bounce was there but it was so minute that if I wanted to have stock crap tires and rims problem solved. They also took my tires and rims and ran them on the new truck. No bounce..smooth as glass. They then checked pinion angles, replaced lift blocks.etc. etc. ..Soooo, they put sensors on my truck as per engineers instructions and ran it and took measurements. RESULT: You have oversize tires and therefore we will not do anything else for you.. They had 24 hours of diagnostic work on truck and it cost me 300 bucks..All I know from all this is that the 285 tires seem to accentuate the hop. I drove the truck with stock tires and rims.. was good..so, I live with it or get divorced, I'm tired of trying to fix it..

Good to hear that the sway bars fixed the issue. I had little doubt that they would. What a lot of people don't know, or think of is that our vehicles act like tuning forks. At a certain frequency all hell can and will break loose! I never thought about this before I came across this post, and never paid attention to my truck...but sure enough, mine does the same thing. Installing the sway bars helps the vibration because it is changing the where the axle and body resonate at. Changing rims and tires and shocks can have the same effect, but not on as drastic of a scale. The people that say there vibration became worse with the sway bars more than likely had other mods to their trucks that helped to line up where everything resonated. If any of you pay attention to motorcycle road racing, the same effect can be seen there. This past season Yamaha struggled with front tire chatter after a frame redesign. Even with changing tire size, compound, and shape along with various fork internals they still could not completely get rid of the problem. It just so happened that they stumbled upon something that should have worked perfectly on paper, but ended up reacting badly when put into the real world. GM won't fix it, because it would take a lot of engineering time and money to make sure the problem wouldn't be moved to another speed, or rear it's ugly head in a dangerous situation. Right now it is an annoyance, not a safety issue. If they changed it, and it became a safety issue...then we all might have to find a new favorite brand quick!!

Having read the last couple of post I will say this. Several members of this forum have taken this information to the dealerships. To avoid spending a number of hours looking for a problem, they are getting GM to pay for the sway bars under customer satisfaction. To date I have more than 40 dealers purchasing 10 or more sets a month.

Unless you would like to get them directly from us, I might suggest this route. I know some dealers are easier to get along with then others. Just food for thought. :)

Frederico Performance and Cognito Motorsports want to thank the forum members for their continued support and patronage.

With any luck, GM would just make your bars standard equipment! Any way you can give us a heads up on how some of those people talked their dealer into them? I know a couple of people that would gladly talk to the dealer to have their truck ride better!

Swaybars standard? HAH! They keep taking things out of the trucks... I have owned an 02, 03, 04, 04.5 and an 06.

Things I "lost"

- cabin air filter
- footwell lights
- gloves and kneeling mat for changing a tire
- chrome on side mirrors
- 2-way lumbar support vs. 1 way in the 06
- instant MPG reading on the DIC
- "Chevrolet" emblem on rear tailgate
- big plastic "wing" on tailgate in favor of cheaper cover
- the size of my side door moldings
- cassette player
- much more...

so does it surprise you there is no rear swaybar? they gotta cust cost somewhere, and who cares if your frame shakes? just put weight in the bed, for gosh sakes, it's a heavy duty truck made to haul junk not be a grocrey getter!

LOL...

Cheers!

With any luck, GM would just make your bars standard equipment! Any way you can give us a heads up on how some of those people talked their dealer into them? I know a couple of people that would gladly talk to the dealer to have their truck ride better!

My knee-jerk advice would be to ask the dealership to make a deal with you. Tell the dealership if the sway bar kit works and corrects the issue to your satisfaction then they pay for the kit and installation and if it doesn’t, which it will, you will pay for it. Or you may tell them about the forum and the fact that other dealerships have been paying for the kit and have had excellent results from installing the kits.

In all honesty the members that have talked their dealerships into paying for the kit are working with people that really bend over backwards to assist their customers. I know a few dealerships in the San Diego area that are that good. I unfortunately also know many more in the area that would tell ya to go pound sand.

Keep in mind that the newer the vehicle the more they will work with you. If it is newer they are more worried about the lemon law and a potential buy-back.

Does the hop cause unevern tire wear? Also Tom can do you have a formal write up with something to take to my dealer? He is clueless when I tried to explain to him.

Is there a service bulletin for this issue?

Does the hop cause uneven tire wear? Also Tom can do you have a formal write up with something to take to my dealer? He is clueless when I tried to explain to him.

Not that I am aware of.

I can write something up and post it here. I will also reference a few of the dealerships that ordered and installed the sway bars for their customers.


Is there a service bulletin for this issue?

No, and in all reality I doubt there ever will be. However there are several GM Area Service Reps that are referring the service managers to me.

I spoke with another dealer and he was aware of the issue. I told him about the sway bars and he knew about it and says the sway bars they use are manufactured by GM. (I think I have seen sway bars on Tahoe's before)
Anyhow I'm taken my truck in tomorrow for them to run diagnostics (road force varioation test) and hopefully they will find the issue. Have you heard of any of the dealers covering this? My truck is out of warranty.

I spoke with another dealer and he was aware of the issue. I told him about the sway bars and he knew about it and says the sway bars they use are manufactured by GM. (I think I have seen sway bars on Tahoe's before)
Anyhow I'm taken my truck in tomorrow for them to run diagnostics (road force varioation test) and hopefully they will find the issue. Have you heard of any of the dealers covering this? My truck is out of warranty.

I have also heard individuals say that GM does make sway bars. But the sway bars they do make are only for the Commercial 3500 stake bed trucks. This rear sway bar does not work on the 2500/3500HD pick-up trucks. The Tahoe, Avalanche, Suburban, and others do come equipped from GM with front and rear Sway Bars. But the 1500, 2500, and 3500’s both regular and HD pick-up trucks do not come from the factory with a rear sway bar. Nor can one be ordered. There is no part # for a rear sway bar from GM available for this line of vehicles.

This is the main reason that individuals need to understand that the rear sway bar is a “NEED” item not something that you should want due to bad handling. It is a matter of safety. They (GM) install a rear sway bar in the vehicles listed above because they carry more passengers than pick-up trucks. But they cannot carry the amount of weight that a pick-up can. Nor do they have an increase in the center of gravity that a pick-up truck has. All the more reason to have a rear sway bar installed.

In addition our Sway Bar kit includes a redesigned front bar that is more reliable and capable of handling the additional loads of a pick-up. A solid front bar verses a hollow bar.

Yes, I have heard of dealerships covering the bars on brand new trucks.

I would appreciate in any info/write up you have along with the dealer information as I'm gonna take my truck in tomorrow.

Tom -
Can you comment on this quote in another thread? Based on your comments in this thread it seems contrary.

"The shudder or bounce in the stock rear suspension is more pronounced with the sway bar package installed but, I think this will be solved with the change to Bilstein shocks." - Anethesia

I too have this bounce and it is annoying. While I don't entirely discount the beam shake issue, I feel this is something new that came on after 30k or so miles. While the beam vibration story implies that it is inherent in the truck design, that has not been my experience. I have replaced the shocks with Bilsteins (from Kennedy) and it was better but not gone. My next check will probably be the U joints, but if this is characteristic of these trucks as they age (although I feel 50k miles is young), I would consider your sway bars to resolve it. It wouldn't be entirely disappointing to have my 2500hd handle more like the Mercedes E430 it replaced.;)

The shudder or bounce that I was referring to is not the beam shake that you guys are discussing here. I was describing a characteristic of this suspension when passing over a small bump, such as an imperfection in the roadway, at any speed. I currently have 17,000 miles on this truck and remain pleased with my investment in the sway bars.