- Thread starter
- #241
That'd be awesome - thanks!
Painful low frequency drone/pressure in cabin
- Thread starter LJE
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Mine are dead center and quite firm. Also that rubber looks pretty rough where you're shining your light.
Having been after you to do those mounts for a while now, I would be really proud if I could claim a small part of actually finding your solution!
I'll be hoping for the best for you, keep us posted.
Having been after you to do those mounts for a while now, I would be really proud if I could claim a small part of actually finding your solution!
I'll be hoping for the best for you, keep us posted.
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Don't know what happened with that post, but good luck.
I’m gonna add my 2 cents since I’ve had these exact same symptoms for years and have yet to find a complete solution. 2000 with 370,000 miles. Slight lift, winch/ bumper, sliders. I have the frame weight.
I’ve replaced just about everything that turns thinking it was driveline related (CVs, front/rear driveshafts, bearings, etc). Also replaced engine and trans mounts. Then went through vacuum hoses and plugs/coil packs. Nothing made much difference. Even tried new tires and wheels.
At one point thought it might be exhaust related so added an exhaust weight/damper. Maybe helped a bit but not much.
I’ve had a suspicion it was related to the torque converter since I’ve noticed a slight vibration at lockup. I pulled the trans pan and it was spotless. Magnets were very clean. So I assumed not trans related. But, added some Lubeguard Shudder Fixx today even though I don’t have what I would describe as shudder. And the booming resonance got markedly worse immediately. I noticed it as soon as I pulled out of my driveway. Makes me think it is the torque converter. My next move is swapping in a used trans/TC and see if it helps.
I’ve replaced just about everything that turns thinking it was driveline related (CVs, front/rear driveshafts, bearings, etc). Also replaced engine and trans mounts. Then went through vacuum hoses and plugs/coil packs. Nothing made much difference. Even tried new tires and wheels.
At one point thought it might be exhaust related so added an exhaust weight/damper. Maybe helped a bit but not much.
I’ve had a suspicion it was related to the torque converter since I’ve noticed a slight vibration at lockup. I pulled the trans pan and it was spotless. Magnets were very clean. So I assumed not trans related. But, added some Lubeguard Shudder Fixx today even though I don’t have what I would describe as shudder. And the booming resonance got markedly worse immediately. I noticed it as soon as I pulled out of my driveway. Makes me think it is the torque converter. My next move is swapping in a used trans/TC and see if it helps.
- Thread starter
- #245
Thanks! We'll see if it helps.
Interesting. Is yours also road speed dependant, and not RPM dependant? If it were TC, I would expect engine RPM (and thus TC RPM) to be the driving factor. I can shift into different gears and maintain the same speed and it stays the same.
- Thread starter
- #247
I *believe* (not sitting in front of my diagnostic manual right now) the TC will only lock up in 4th gear or higher (assuming you've got a 5-speed, if you're got a 4 speed I think it would be 3rd or higher).
You should be cruising at a steady speed and see/feel a slight drop in RPMs when the TC locks up.
I need to amend my previous description. After a long road trip this past week, I realized I have two separate issues: a slight vibe that is torque converter related and is dependent on RPMs. And a booming resonance that is speed dependent. It happens around 25 mph and again at 55. I was able to reduce the booming resonance significantly by replacing rear trailing arms and flipping rear driveshaft so that slip yoke is at transfer case. Still have the boom at idle though. Still need to replace panhard and see if that completely removes it.
<TLDR> Have you check your tailgate bump stops?
This is a long technical post, but let me try and explain.....
I've had fun reading through your thread, you're certainly super dedicated to arriving at a solution and it's obvious that you have an engineering background from your approach.
It sounds like you have/had 3 separate issues that may or may not be related.
1. 40Hz hum at 60 mph - resolved until the dead UJ
2. Idle boom
3. Poor small bump compliance
40Hz hum
As you identified the 40Hz hum is amplified by cabin resonance. The cabin acts as a tube which has a first resonant frequency when the cabin length is half the full wave length (half wave resonance). At 40hz, that's 4.125m. It can be longer than the front to back measurement from front to rear as the air path can curve from the bottom of the boot (trunk), over the seats and down into the footwells. The reason it sounds okay in the mid row and worst in the front and rear is because of the resonance - the middle is a 'node' or null point, with the ends being anti-nodes or maxima. This resonance in fixed and you can't change it without changing the size of the cabin or massive changes in absorption (such as cloth rather than leather seats), but you can change how it is excited.
As you've found through replacing the TX case rear bearing (and the now dead UJ) the 40Hz vibration from the rear driveline excites the body through vibration and then cabin mode through panel radiation. The transfer path (the route the vibration takes) will be complicated, but will go through the powertrain mounts into the chassis (frame) and then into the body. If your body mounts are knackered and snubbing (bottomed out) then it could make the transfer path worse meaning more energy gets to the body structure to excite that cabin mode (this also applies to your idle boom). Replacing these should help, but may not.
Once the energy is in the body how does it become sound? various body panels will vibrate and work just like a speaker, driving the air in the cabin. They will all have their own resonant frequencies and will all constructively/destructively interfere with each other. One of the big panels that likes to vibrate at low frequencies in SUV's is the tailgate. I worked on one in the past that had a first resonance on its seals of 38Hz so in the range. It was a smaller vehicle than the 100 series, but was a single piece tailgate. It had awful booming on impacts. *If* your tailgate is resonating that could make your vehicle more sensitive to 40Hz than your neighbours 100 series. The resonance of the tailgate can be played with by manufacturers by adjusting seal and bump stop stiffness. If your bump stops aren't engaging properly, the tailgate may be bouncing on the seal and amplifying the issue you have, which is driveline vibration. So have a look there, see if adjusting the bump stops so the tailgate sits harder on them helps.
Someone's point earlier in the thread about roof bonding was interesting - when the bonding fails the roof resonant frequency will drop. That new resonance could well excite the cabin mode which explains why it fixed other peoples issue.
Idle boom
This sounds like alignment of engine orders (mostly firing and harmonics) with various resonant frequencies. I can't remember what the idle speed on my 100 is, but at a typical 600rpm the dominate frequency from a V8 is, you guessed it - 40Hz. Looks like Toyota address this with a the tuned absorber on the chassis (frame) in the US, European and JDM vehicles don't seem to get that part. This absorber is basically a lump of metal mounted on rubber that is tuned to have the same frequency as the problem vibration. It reacts to the vibration by going into resonance and in the process absorbs a portion of the energy in the system. Interesting sidenote - I think it's Discovery/LR3 that has 2 20kg (44lb) tuned absorbers on the chassis!
If your body mounts are shot they will pass more energy to the body, if your tailgate bump stops aren't great it could be converting that energy into noise.
Firing order excitation is a function of engine design so it's unlikely your rebuild is the cause. Rebuild issues are typically 0.5 order (every other rotation - driven by combustion), 1st order (driven by engine balance) or 2nd order (if you screwed something up that affects a single bank).
Small bump compliance
Interesting that another commentor saw his get better over time. I have AHC on my Toyota (we got that in Europe on TLC although mine is a JDM import with it) and don't notice any issue and I'm pretty sensitive to small bump. Can't think of anything more helpful though, sorry.
Thanks for this thread, I clicked on it as I have a mild 'drone' at ~60mph in mine (on 33's so comparable prop shaft speed). It's not bad enough that I've done any serious thinking about it before, but this thread has focused my mind on the problem and it feels likely that it's related to the play it the rear prop shaft slip joint. My rear prop front UJ failed a couple of years ago in a similar way to yours - it felt fine on the truck, but as as soon as it was unbolted it was obvious that it was roached - it barely rotated. It's possible this has also damaged the TX case rear bearing, so I'll be taking a close look at that too.
This is a long technical post, but let me try and explain.....
I've had fun reading through your thread, you're certainly super dedicated to arriving at a solution and it's obvious that you have an engineering background from your approach.
It sounds like you have/had 3 separate issues that may or may not be related.
1. 40Hz hum at 60 mph - resolved until the dead UJ
2. Idle boom
3. Poor small bump compliance
40Hz hum
As you identified the 40Hz hum is amplified by cabin resonance. The cabin acts as a tube which has a first resonant frequency when the cabin length is half the full wave length (half wave resonance). At 40hz, that's 4.125m. It can be longer than the front to back measurement from front to rear as the air path can curve from the bottom of the boot (trunk), over the seats and down into the footwells. The reason it sounds okay in the mid row and worst in the front and rear is because of the resonance - the middle is a 'node' or null point, with the ends being anti-nodes or maxima. This resonance in fixed and you can't change it without changing the size of the cabin or massive changes in absorption (such as cloth rather than leather seats), but you can change how it is excited.
As you've found through replacing the TX case rear bearing (and the now dead UJ) the 40Hz vibration from the rear driveline excites the body through vibration and then cabin mode through panel radiation. The transfer path (the route the vibration takes) will be complicated, but will go through the powertrain mounts into the chassis (frame) and then into the body. If your body mounts are knackered and snubbing (bottomed out) then it could make the transfer path worse meaning more energy gets to the body structure to excite that cabin mode (this also applies to your idle boom). Replacing these should help, but may not.
Once the energy is in the body how does it become sound? various body panels will vibrate and work just like a speaker, driving the air in the cabin. They will all have their own resonant frequencies and will all constructively/destructively interfere with each other. One of the big panels that likes to vibrate at low frequencies in SUV's is the tailgate. I worked on one in the past that had a first resonance on its seals of 38Hz so in the range. It was a smaller vehicle than the 100 series, but was a single piece tailgate. It had awful booming on impacts. *If* your tailgate is resonating that could make your vehicle more sensitive to 40Hz than your neighbours 100 series. The resonance of the tailgate can be played with by manufacturers by adjusting seal and bump stop stiffness. If your bump stops aren't engaging properly, the tailgate may be bouncing on the seal and amplifying the issue you have, which is driveline vibration. So have a look there, see if adjusting the bump stops so the tailgate sits harder on them helps.
Someone's point earlier in the thread about roof bonding was interesting - when the bonding fails the roof resonant frequency will drop. That new resonance could well excite the cabin mode which explains why it fixed other peoples issue.
Idle boom
This sounds like alignment of engine orders (mostly firing and harmonics) with various resonant frequencies. I can't remember what the idle speed on my 100 is, but at a typical 600rpm the dominate frequency from a V8 is, you guessed it - 40Hz. Looks like Toyota address this with a the tuned absorber on the chassis (frame) in the US, European and JDM vehicles don't seem to get that part. This absorber is basically a lump of metal mounted on rubber that is tuned to have the same frequency as the problem vibration. It reacts to the vibration by going into resonance and in the process absorbs a portion of the energy in the system. Interesting sidenote - I think it's Discovery/LR3 that has 2 20kg (44lb) tuned absorbers on the chassis!
If your body mounts are shot they will pass more energy to the body, if your tailgate bump stops aren't great it could be converting that energy into noise.
Firing order excitation is a function of engine design so it's unlikely your rebuild is the cause. Rebuild issues are typically 0.5 order (every other rotation - driven by combustion), 1st order (driven by engine balance) or 2nd order (if you screwed something up that affects a single bank).
Small bump compliance
Interesting that another commentor saw his get better over time. I have AHC on my Toyota (we got that in Europe on TLC although mine is a JDM import with it) and don't notice any issue and I'm pretty sensitive to small bump. Can't think of anything more helpful though, sorry.
Thanks for this thread, I clicked on it as I have a mild 'drone' at ~60mph in mine (on 33's so comparable prop shaft speed). It's not bad enough that I've done any serious thinking about it before, but this thread has focused my mind on the problem and it feels likely that it's related to the play it the rear prop shaft slip joint. My rear prop front UJ failed a couple of years ago in a similar way to yours - it felt fine on the truck, but as as soon as it was unbolted it was obvious that it was roached - it barely rotated. It's possible this has also damaged the TX case rear bearing, so I'll be taking a close look at that too.
- Thread starter
- #251
Hey - thanks for the super insightful post! You put into words (very clearly I might add!) exactly what I've eventually come to the conclusion of here over the past few months. My 'bad' U-joint turned out to be fine I think. Replacing it did nothing.
I'd actually adjusted the tailgate bump stops earlier because I had that exact thought - and apparently that's an issue with the Grand Highlanders. No change there though, no joy.
My roof & hood have been re-bonded to the skeleton frame under them at this point - the hood was very much delaminated, the roof not nearly as much. Hood seemed to make a difference in reducing overall severity.
Then, as I continued to dig and dig and dig, the 'exhaust boom at idle' TSB came up. It was very apparent that based on the tuned mass dampers that Toyota was suggesting to add to the muffler, that there is an 'issue' with 40hz resonance getting pick up by the frame. Toyota provided a list of different part number dampers to put on the muffler - the damping frequencies were all slightly different, but they were centered right on the 40hz mark.
That tells me that the frame is prone to picking up 40hz vibration that gets created by the exhaust at idle. In my case, I'm confident that the exhaust isn't an issue here (well, other than that slight drone at idle), but the fact that the frame is sensitive to 40hz was good to confirm.
FWIW, there are WAY more things to do in that TSB other than 'slap the frame weight on it', but again, all centered around trying to reduce the 40hz energy that's getting generated by the frame.
OK - so the frame wants to resonant at 40hz, got it. This then gets exacerbated by the fact that the cabin also wants to resonate at 40hz -like you said, the size of the cabin is right in the range of a 40hz sound wave. Seems like it's a recipe for disaster... but the majority of folks have zero issues with this, so what gives?
The question then becomes: why is my LX SO MUCH WORSE than others in this regard?
At this point, I think it has to come down to body mount bushings. Like you aptly pointed out - bad body mount bushings are going to allow the frame (which wants to resonate at 40 hz) to couple to the cabin, exciting the cabin with the 40-ish-hz energy coming off the frame, causing the audible resonance by shaking the entire body, not just one panel. This seems like it would take a lot of energy, but the fact that you can get mild cabin drone at idle due to this phenomenon from the exhaust seems to indicate that it's possible when you're at speed and have a lot of spinning components right at those frequencies to induce excitation.
Bad body mounts would also (potentially) explain why my AHC feels terrible over little stuff - things that should be getting absorbed by the body mount bushings are instead dumping that energy straight into the cabin. This is all stuff that's too small/short duration to get absorbed by the AHC, so the bad body mounts could be turning my LX into a giant, instantaneously rigid system.
Finally, this may also explain why my cabin resonance is significantly worse when I have another person in the front seat with me - I think that the additional weight is enough to make the bushings sag even further/couple the body even more to the frame. That sounds silly, but it's the only thing I could imagine that would cause it to be worse. This phenomenon confirmed via multiple trips over the same route - if it was just me, cabin resonance was very minimal (but not quite gone). Put my wife in the passenger seat & now both of our ears are screaming. Wild, but true. I'm also somewhat convinced that it was better when it was very cold outside - perhaps stiffer bushings would prevent as much sag & coupling? Seems counter intuitive, but again, looking back in this thread, my suspension felt worse (and cabin resonance was bad) last summer. It got better in the winter, and then got bad again as soon as it warmed up. Not sure what else could explain this.
So, that's the theory right now. It's sorta like 'Alex's one universal bushing theory to tie all his problems together'. As soon as I get my truck back (fabricator finally started on the rear bumper after having my truck for four weeks...) I'm going to swap those bushings and see what happens. I could be wrong (has happened a lot in this thread), but it's a pretty sound theory. It would be odd to me that my body mount bushings seem to have failed in a unique way compared to every one else, but I guess there's a first for everything.
The chassis isn't necessarily resonating at 40Hz. Either way the energy will be passing through it, so it's a reasonable place to put the absorber. The passenger having an impact could be a couple of things, first as you say, the body mounts being loaded up. Secondly the seat could have a resonance of its own or on the body of the vehicle. When you put someone in the seat it will shift that resonance either into the 40Hz region making the noise worse or away from the 40hz region where it may have been cancelling another resonance! Ideally you'd drive the truck with no one in either front seat, but that's a challenging prospect
.Regarding your AHC, can't remember from the thread, but I assume you've checked top and bottom mounts on the hydraulic actuators? They have a big impact on small bump compliance.
- Thread starter
- #253
Both bottom *and* top AHC 'shock' bushings are new (as the holes I had to drill & then patch in my floor in the cargo area can attest to). The only bushings that aren't new in the entire vehicle are the body mounts.The chassis isn't necessarily resonating at 40Hz. Either way the energy will be passing through it, so it's a reasonable place to put the absorber. The passenger having an impact could be a couple of things, first as you say, the body mounts being loaded up. Secondly the seat could have a resonance of its own or on the body of the vehicle. When you put someone in the seat it will shift that resonance either into the 40Hz region making the noise worse or away from the 40hz region where it may have been cancelling another resonance! Ideally you'd drive the truck with no one in either front seat, but that's a challenging prospect
Regarding your AHC, can't remember from the thread, but I assume you've checked top and bottom mounts on the hydraulic actuators? They have a big impact on small bump compliance.
If the frame doesn't want to resonant at 40hz, why would the frame weight work to grt rid of the cabin boom at idle? I understand that the frame could just be passing energy in the 40hz band, but it seems like for the (relatively) small mass of the frame weight to have an effect, it would need to have been targeted to a resonant mode of the frame.
To be clear (if it wasn't already, hahaha), I'm no vibrations expert. The closest expertise & experience I have is pyroshock testing & hardening, but that's an entirely different beast than "low frequency" continuous vibration.
The energy is passing through the frame as vibration waves. The absorber is tuned to take that particular frequency of energy and absorb it as heat in the rubber. It's more effective to put an absorber on the resonant component (hence the muffler absorbers), but they work on non-resonant parts too. None of this is to say that the frame is not resonating, just that it's not determined that it is.
The fact that Toyota chose the spot they dis suggests that it's the most active part of the frame, and it's close to the front body mounts, so I would take a guess that if the body mounts are responsible they are the ones most likely to be the path. But if it were me I would be replacing all of them....
- Thread starter
- #255
Absolutely - the additional work required to replace all the body mount bushings vs just one on each side is negible, since even if you were only doing one you'd still have to unbolt them all to get the front one out. I've got them all sitting here, just need to get my vehicle back...
- Thread starter
- #256
OK, finally back for an update:
Bodymount bushings: Not super difficult to do on a rust free truck, but no difference once done. Boo.
Swapped transfer case with spare last night. No difference. Boo.
For the 931th time on this problem, stumped again. There is a definite difference when I pull the front drive shaft (which is something I also noticed way back at the beginning of this problem and after I grenaded my front diff) - gets better (narrows the speed band that induces the resonance), but not entirely gone.
Front D/S feels fine, u-joints feel fine, but goinf to pull it out again for a while and see what I think. The only thing left in the drive train as this point that *hasn't* been changed out are: front drive shaft, rear axle shafts, rear axle housing, transmission, and one front CV.
As a reminder, it's entirely roadspeed depedentant. 45-60 mph is where it's the worst - doesn't matter if I'm in 4th or 5th gear. I'm going to try to compile a list of all the things I've done chasing this to be able to paint a better picture in the future.
Bodymount bushings: Not super difficult to do on a rust free truck, but no difference once done. Boo.
Swapped transfer case with spare last night. No difference. Boo.
For the 931th time on this problem, stumped again. There is a definite difference when I pull the front drive shaft (which is something I also noticed way back at the beginning of this problem and after I grenaded my front diff) - gets better (narrows the speed band that induces the resonance), but not entirely gone.
Front D/S feels fine, u-joints feel fine, but goinf to pull it out again for a while and see what I think. The only thing left in the drive train as this point that *hasn't* been changed out are: front drive shaft, rear axle shafts, rear axle housing, transmission, and one front CV.
As a reminder, it's entirely roadspeed depedentant. 45-60 mph is where it's the worst - doesn't matter if I'm in 4th or 5th gear. I'm going to try to compile a list of all the things I've done chasing this to be able to paint a better picture in the future.
Sorry to see you're still fighting this issue. I'm sure this is not the issue/fix, but have you replaced this little bushing? I rarely see it mentioned on the forums and I'm sure you've already swapped it but wanted to throw it in the ring.
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- #258
I haven't actually swapped that - I can't actually imagine in my brain where that goes. Do you have a description for it?
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- #260
Oh, interesting - I'll take a look at those and likely order the two to knock it off the list.
