Elripster

Ya know, you can blame wheels, etc... all day long. The bottom line is every other vehicle runs them just fine. These trucks require unicorn grade carparts to be livable which even if you find them, will become sub-unicorn grade when the age/wear. Anyway, your money, spend it where you'd like. You asked if it was risky, I am an engineer and I would suggest steering clear until the next body restyle. If you look up under the headliner, you will see there is very little metal up there. The roof bows are very flimsy and they support a paper-thin roof. That is the heart of the issue. Frank

I would say too risky. This issue is a design flaw. The trucks have terribly thin sheetmetal that is poorly supported. The next body restyle will hopefully address it. Frank

I did model them in SolidWorks but I have not built to the model. I just made them to-fit with my band saw. So my prototypes are urethane bar stock. I used (2) 1.5" square pieces (24" length) glued together but going forward I would use something harder. Maybe something like this... https://www.mcmaster.com/#=1ava2d9 I also suspect going to 36" will help as well. I use 2" wide weather stripping between the bars and roof itself. I drilled holes to get the radii and then cut into them tangentially with the band saw to try to mimic the shape of the roof racks. I did have to purchase the roof racks separately since my truck did not come with them. The good news is that I am completely happy with this truck. I went up a size to some more off road worthy tires since I camp and occasionally get the truck into 4 low (locker works!). It rougher as expected but it's not different now than any other truck with larger harder tires. If this does not get rid of the booming, Dynamat or equivalent will. Buffeting is a very low frequency phenomenon where the booming is higher in frequency and well addressed by Dynamat or similar.

You can just see them here...

Folks, the roof is the problem. I bought some hard rubber stock from MMC and fabbed up some spacers to wedge between my roof rack and roof and the problem disappeared. Take off the spacers and it comes right back. My 'burban is awesome now with the spacers in place. These trucks are made of extremely thin sheetmetal. The roof, short of welding it to the bows, will just pull itself free. You need to hold it down by some means. I suppose you could rivet it to the bows but you'd need to seal it very well. Maybe one could bedliner the roof to stiffen it if they wanted. Anyway, if anyone has this issue, you have two choices. Make GM buy it back or find a way to hold the roof down. All the tire combos, etc... might make it a bit better, but rest assured you will find a road or speed condition that gets the roof flapping. Hold the roof down, you can run all kinds of tires, etc... just like any other normal vehicle, and enjoy them. Frank

That was me. It works. I don't have a lot more to contribute in addition to what I already have. I still see people trying to do things that reduce the inputs to the chassis that excite the roof and get it buffeting. That's fine but trust those tires will wear, or your shocks will be extra cold one morning, or you will find a stretch of road with the right bump pattern.... and it will buffet again if you don't pin or otherwise hold the roof down. Dynamat on the underside of the roof also does wonders for the booming. I dig my truck after wedging something between the roof and cargo rail + dynamat treatment. Frank

That was me. It works. I don't have a lot more to contribute in addition to what I already have. I still see people trying to do things that reduce the inputs to the chassis that excite the roof and get it buffeting. That's fine but trust those tires will wear, or your shocks will be extra cold one morning, or you will find a stretch of road with the right bump pattern.... and it will buffet again if you don't pin or otherwise hold the roof down. Dynamat on the underside of the roof also does wonders for the booming. I dig my truck after wedging something between the roof and cargo rail + dynamat treatment. Frank

"Intact" can mean a lot of things. The roof can be touching them at rest and lift and buffet at speed. Find a way to strap something to the roof and hold it down. If the issue is unchanged than maybe you have other issues. Otherwise, the roof is the large expanse of sheetmetal that can change the interior air volume and cause the buffeting. Frank

We are talking about tolerances. The Cadi might be Ok. If so great. Others, not so lucky Frank

We can go round and round on body mounts, shocks, etc... but at the end of the day, the truck must tolerate the real world. I suggest for all having issues that they pin down the roof and report back.

How do you delete a post?

I now have over 22k miles on my Z71 Burban. I can make the buffeting come and go at will and by doing so have confirmed the issue. First, let's talk about what the issue is not. - Shocks/Tires/AFM.... all of these are normal features of vehicles and vehicles should not boom and vibrate due to them. No past generations of Surban had our issues and I doubt the next will either. Typical vehicles should not need unicorn grade car parts to function properly. I have put so many suspension mods on vehicles and never had these issues. - Because it is a truck - not... I have been driving trucks for years and none of them ever did this. Now, my burban doesn't do it either. It is the luxury vehicle I bought. It is the vehicle that GM execs drove thousands of miles in before signing off on release because there is no way GM execs would have tolerated these issues if their test mules had exhibited them. The issue from a high level stems from weight saving efforts which resulted in paper thin sheet metal. To keep the sheet metal from vibrating (booming) and flexing (buffeting) it absolutely HAS to be attached firmly to its braces. In our case, the roof, due the roof panel being compressed from the edges, wants to pop off of the roof bows rather than be stretched tight against the roof bows (how they should be). As a result, the roof pops off and you are driving in a giant drum. This is a manufacturing defect. You all can search on my screen name if you want to see what was done to my truck but the real story is that I made some plastic pieces to wedge between the roof rack rails and roof. You could make some out of a 2X4's if you wanted to test this (yeah, that would look rather 'neck on one of our trucks) When they are in place, zero booming and buffeting. Remove them, both come back. Keep in mind my dealer put Dynamat on my roof and lots of extra glue to hod the roof to the bows. When the bows again became detached, the issues returned. Put the roof back onto the bows, the issues go away. I know of no other better way to confirm root cause than to be able to make a chance and get an issue to come/go at will. Dealers cannot redesign, only repair. So they are trying everything in the book to not introduce the forces that cause the noises. Unfortunately, this is a mission impossible. There will always be a road surfaces, temperatures, etc... that produce the issues. Automakers know this. Vehicles have too be designed to tolerate these issues. Find a way to pin your roof down and you to can get the truck you thought you were buying. Frank I now have over 22k miles on my Z71 Burban. I can make the buffeting come and go at will and by doing so have confirmed the issue. First, let's talk about what the issue is not. - Shocks/Tires/AFM.... all of these are normal features of vehicles and vehicles should not boom and vibrate due to them. No past generations of Surban had our issues and I doubt the next will either. Typical vehicles should not need unicorn grade car parts to function properly. I have put so many suspension mods on vehicles and never had these issues. - Because it is a truck - not... I have been driving trucks for years and none of them ever did this. Now, my burban doesn't do it either. It is the luxury vehicle I bought. It is the vehicle that GM execs drove thousands of miles in before signing off on release because there is no way GM execs would have tolerated these issues if their test mules had exhibited them. The issue from a high level stems from weight saving efforts which resulted in paper thin sheet metal. To keep the sheet metal from vibrating (booming) and flexing (buffeting) it absolutely HAS to be attached firmly to its braces. In our case, the roof, due the roof panel being compressed from the edges, wants to pop off of the roof bows rather than be stretched tight against the roof bows (how they should be). As a result, the roof pops off and you are driving in a giant drum. This is a manufacturing defect. You all can search on my screen name if you want to see what was done to my truck but the real story is that I made some plastic pieces to wedge between the roof rack rails and roof. You could make some out of a 2X4's if you wanted to test this (yeah, that would look rather 'neck on one of our trucks) When they are in place, zero booming and buffeting. Remove them, both come back. Keep in mind my dealer put Dynamat on my roof and lots of extra glue to hod the roof to the bows. When the bows again became detached, the issues returned. Put the roof back onto the bows, the issues go away. I know of no other better way to confirm root cause than to be able to make a chance and get an issue to come/go at will. Dealers cannot redesign, only repair. So they are trying everything in the book to not introduce the forces that cause the noises. Unfortunately, this is a mission impossible. There will always be a road surfaces, temperatures, etc... that produce the issues. Automakers know this. Vehicles have too be designed to tolerate these issues. Find a way to pin your roof down and you to can get the truck you thought you were buying. Frank I now have over 22k miles on my Z71 Burban. I can make the buffeting come and go at will and by doing so have confirmed the issue. First, let's talk about what the issue is not. - Shocks/Tires/AFM.... all of these are normal features of vehicles and vehicles should not boom and vibrate due to them. No past generations of Surban had our issues and I doubt the next will either. Typical vehicles should not need unicorn grade car parts to function properly. I have put so many suspension mods on vehicles and never had these issues. - Because it is a truck - not... I have been driving trucks for years and none of them ever did this. Now, my burban doesn't do it either. It is the luxury vehicle I bought. It is the vehicle that GM execs drove thousands of miles in before signing off on release because there is no way GM execs would have tolerated these issues if their test mules had exhibited them. The issue from a high level stems from weight saving efforts which resulted in paper thin sheet metal. To keep the sheet metal from vibrating (booming) and flexing (buffeting) it absolutely HAS to be attached firmly to its braces. In our case, the roof, due the roof panel being compressed from the edges, wants to pop off of the roof bows rather than be stretched tight against the roof bows (how they should be). As a result, the roof pops off and you are driving in a giant drum. This is a manufacturing defect. You all can search on my screen name if you want to see what was done to my truck but the real story is that I made some plastic pieces to wedge between the roof rack rails and roof. You could make some out of a 2X4's if you wanted to test this (yeah, that would look rather 'neck on one of our trucks) When they are in place, zero booming and buffeting. Remove them, both come back. Keep in mind my dealer put Dynamat on my roof and lots of extra glue to hod the roof to the bows. When the bows again became detached, the issues returned. Put the roof back onto the bows, the issues go away. I know of no other better way to confirm root cause than to be able to make a chance and get an issue to come/go at will. Dealers cannot redesign, only repair. So they are trying everything in the book to not introduce the forces that cause the noises. Unfortunately, this is a mission impossible. There will always be a road surfaces, temperatures, etc... that produce the issues. Automakers know this. Vehicles have too be designed to tolerate these issues. Find a way to pin your roof down and you to can get the truck you thought you were buying. Frank

I now have over 22k miles on my Z71 Burban. I can make the buffeting come and go at will and by doing so have confirmed the issue. First, let's talk about what the issue is not. - Shocks/Tires/AFM.... all of these are normal features of vehicles and vehicles should not boom and vibrate due to them. No past generations of Surban had our issues and I doubt the next will either. Typical vehicles should not need unicorn grade car parts to function properly. I have put so many suspension mods on vehicles and never had these issues. - Because it is a truck - not... I have been driving trucks for years and none of them ever did this. Now, my burban doesn't do it either. It is the luxury vehicle I bought. It is the vehicle that GM execs drove thousands of miles in before signing off on release because there is no way GM execs would have tolerated these issues if their test mules had exhibited them. The issue from a high level stems from weight saving efforts which resulted in paper thin sheet metal. To keep the sheet metal from vibrating (booming) and flexing (buffeting) it absolutely HAS to be attached firmly to its braces. In our case, the roof, due the roof panel being compressed from the edges, wants to pop off of the roof bows rather than be stretched tight against the roof bows (how they should be). As a result, the roof pops off and you are driving in a giant drum. This is a manufacturing defect. You all can search on my screen name if you want to see what was done to my truck but the real story is that I made some plastic pieces to wedge between the roof rack rails and roof. You could make some out of a 2X4's if you wanted to test this (yeah, that would look rather 'neck on one of our trucks) When they are in place, zero booming and buffeting. Remove them, both come back. Keep in mind my dealer put Dynamat on my roof and lots of extra glue to hod the roof to the bows. When the bows again became detached, the issues returned. Put the roof back onto the bows, the issues go away. I know of no other better way to confirm root cause than to be able to make a chance and get an issue to come/go at will. Dealers cannot redesign, only repair. So they are trying everything in the book to not introduce the forces that cause the noises. Unfortunately, this is a mission impossible. There will always be a road surfaces, temperatures, etc... that produce the issues. Automakers know this. Vehicles have too be designed to tolerate these issues. Find a way to pin your roof down and you to can get the truck you thought you were buying. Frank

Not permanently. Mine took about 2k miles to show up. After being fixed it probably took another few thousand miles to return. I will say the the Dynamat applied by my dealer to the roof cured the booming especially that associate with the V4 mode. All of the extra foam/glue has reduced the buffeting even after the rearward bows have come detached, but in the end, the roof won't stay attached so be it vibrating car parts or non-smooth road surfaces, the truck will buffet. If you have a vibration issue, that will need to be addressed regardless since unbalanced spinning parts will be a problem unto themselves.

Buffeting and vibrations while related are two different issue. Vehicles vibrate for all sorts of legitimate reasons, like rough pavement. Buffeting is a change in air pressure in the cabin which can be due to vibrations or resonances between the air within and outside of the cabin. To address the buffeting, and for the most part the booming, the roof simply has to be fasted down. Since our stock trucks have a rake, as speed increases there is a lift phenomenon due to the Bernoulli effect (air in cab is still while air over roof is moving) and force due to pushing air up as the vehicle travels. At the point those two forces cross, buffeting can occur even on a smooth road. I have noticed repeatedly that if I increase speed I can get buffeting to decrease. Unfortunately the speed limit does not appreciate that. If the roof is detached, of course it will boom and buffet due to the road inputs. One thing lowering is doing is leveling the vehicle. The lifting forces then are dominant and so that component of buffeting is eliminated. If lowering is also addressing a resonance issue then two sources of roof excitement are addressed. However, in all cases, the buffeting is like the running nose and the detached roof is the sinus infection. We need to push our dealers to fix the problem and not focus on the symptom which they can easily dismiss as "normal". GM admitted guilt when they issued the roof TSB so if you fight that angle (roof properly repaired, symptoms only help find problems, not the problem themselves) you will win. Frank

Mine was fine,however, all but the most forward bow have since come detached and issues are back.

But, this does bot prove that ride height did it. Can you cut a stock coil and test on a problem vehicle? That would help to see if lowering vs spring rate fixed it. Sent from my SM-N910V using Tapatalk

Well.... is it lowering or changing the spring rate? I'd say changing the spring rate is likely since this is a spring-mass-damper system and if you want to change the resonant frequency you have to change one of those. How can one get a hold of a set of Z71 height progressive rate springs? That applies to a truck with issues would be telling. Frank

This is probably not something you could do as I am sure you are working to keep up with customer demand but.... if it is possible, would you be able to try changing only the springs, test drive, then shocks, test drive,... just to see if one or the other make a difference?

Do you have a feel for what part of the lowering is addressing the issues? For example, are you using stiffer springs and shocks? I don't want to lower my truck, heck I'd rather raise is, but if stiffer springs and shocks are part of lowering than the same might work for stock or lifted right height vehicles. Frank

It is definitely a resonant frequency issue, however trucks without ANC have booming just as trucks with it do so I am going to say it is due to the body being highly susceptible to typical road inputs which is the opposite of how the body should be designed. ANC might not be capable of damping the booming noise. As you mentioned, the thinner metal is most certainly a large part of the issue. Disrupting the disturbing frequency can help but only so much. The body is the issue. The Dynamat applied to the inner roof of my truck by my dealer pretty much killed the booming. Booming is ever so slight and most people cannot hear. One rear roof bow is not attached and I have a slight bit of buffeting. I will say, when all the roof bows are attached, and with the Dynamat, the truck is perfect. Frank

Well I think everyone who had their bows reattached should make sure the bows are still attached before concluding that attached roof bows still buffet. I would not be surprised if people picked up their trucks, shut the door, and popped off a bow before they even left the lot. My dealer said they applied an exceptional amount of glue in an attempt to keep the bows attached and while they were the buffeting was gone. As I said, as the bows came detached the buffeting returned. Also, I wonder how many interchange booming with buffeting? Adding mass like Dynamat damps motion but does not stiffen. The added mass requires more energy to get it to oscillate at a given frequency. The hope is that there is not enough energy and thus vibrations are not transferred as noise. All things equal, adding mass reduces the natural frequency. Buffeting is such a low frequency that it stands to reason that the Dynamat has little to no effect as all it could to move the resonant frequency down into the range of buffeting though I suspect the forcing side of the function here (road, wind input) is sufficiently strong as to dwarf the impact of Dynamat. I completely get automotive NVH. We convert semis to EV's and rest assured drivers hear all sorts of "noises" that bother them but in fact always there, just drowned out by a 12 litre diesel. Frank

Critical speeds, modes, etc... are really getting to far into the weeds here. Vehicles must be tolerant to disturbances to provide acceptable NVH characteristics. We engineers are very familiar with this. The flimsy body simply moves the resonant frequencies into that of the disturbances. It nod impassable to eliminate all disturbances hence why stiff well damped structures are necessary. As for the Dynamat comment, Dynamat in no way stiffens anything thus it stands to reason that it would not address buffeting. It is much more effective at higher frequency noises like the booming. It works by adding mass and damping those higher frequencies. My truck's buffeting was completely addressed by the roof bows and the booming by the Dynamat. Then the bows came detached and the buffeting returned but the booming is much reduced. The roof is definitely key to the buffeting to the point that driving the truck with the headliner removed one could observe the buffeting via roof movement and place ones hand on the roof and make it stop. Based on the tone made by tapping the sheet metal below the rear window I believe booing could be further addressed by Dynamat there. Frank Sent from my SM-N910V using Tapatalk

Actually this is entirely the problem being that the body flexes too much and is not stiff enough. The stiffer the frames the better as far as ride and handling are concerned. This encourages the suspension to absorb impacts rather than the frame and thus body to flex transferring the force to the occupants. The weight saving measures have clearly made the body sheet metal much thinner and thus it resonates at frequencies typically encountered by vehicles. stiffening the body will raise the natural frequencies above the disturbing frequencies much as it was on the thicker skinned trucks of previous generations. Frank

Thanks Yahtzee! My truck is back in the shop. Apparently the differential needs some work. We shall see if this helps. I am about ready to get some urethane bar stock, cut some wedges, and put them between the cross rails and roof to hold it down against the bows. Frank Sent from my SM-N910V using Tapatalk