Painful low frequency drone/pressure in cabin

[Bisho]

I've been meaning to come back to this thread!

So I went to COTR in October, waaaaaaah waaaaaah sound and all. Had an absolute blast. Blew my front diff, so hadn't been driving the truck much. But, can confirm my waaaaah sound was still present without the front diff spinning at all (no drive shaft, no hub flanges) on the drive back.

I put the rear up in the air, and with the tires spinning at 50mph, there was a weird rhythmic tapping sound you could hear with a stethoscope, and even without the stethoscope, the rear diff sounded *rough*. Sorta sounded like some rocks bouncing around in there. Again, when I changed the diff fluid a 1k miles ago when rebuilding the truck, the rear magnet had a lot of smoo on it - significantly more than usual. No chunks of teeth, just a whole bunch of paste.

Fast forward to now. I just finished rebuilding two 'new' diffs with ARB lockers, new bearings, and used 4.30 gears. Swapped them in over Christmas, and have done a couple drives since.

'Waaaaaaah.... Waaaaaaah' sound (I think) is gone, but haven't done much highway driving during break in. Hoping that we've solved this one though. If it's not solved, then it must be the T-case. I have a spare one of those too now, so if that's the case I can swap.

However... The 'ear pressure' thing is still definitely around. Not nearly as bad as it was when I started this thread, but still there at lower speeds/back roads. I'm highly suspicious of my AHC at this point - despite ALL suspension bushings being new OEM (front/rear upper and lower control arms, and upper/lower AHC 'shock' bushings), AHC globes and fluid being new, and neutral pressures being correct, the ride over small bumps/expansion joints/sealer joints in the road is TERRIBLE. Let me repeat that. IT IS TERRIBLE.

My 2003 Sequoia with a somewhat sporty Eibach suspension and ALL polyurethane bushings in the front rides SO MUCH BETTER. I know I'm shouting here, but I'm just trying to communicate how rough it is.

Big bumps/dips are absorbed super nice, but all the little stuff feels as if I'm riding on concrete (have I mentioned how bad it is?). I *believe* the overly stiff AHC is exciting resonance in the cabin (imagine hitting a drum with a stick) that's causing this problem. It's really bad driving down my gravel driveway (very bumpy), paved roads seem to vary, so I definitely think it's suspension related.
This is something I've noticed this entire time, but I've been focused on the higher speed highway type driving. There's a number of threads dating back a decade on this exact AHC problem with no resolution, so I've got my work cutout for myself to figure it out. We've currently got a ton of snow on the ground here in Indiana, so I need to undercoat the vehicle before I start driving again.

Thanks for following up!

What tires are you running, and how much air pressure?

 

[LJE]

What tires are you running, and how much air pressure?

Falken Wildpeak 'C' rated tires, 35-ish PSI. Doesn't change with tire pressure though, tried that.

I drove the LX to work yesterday - pulling up the spectrum analyzer app again, I'm actually still getting a low-frequency (40hz-50hz) vibration that directly correlates to driveshaft speed. This is exactly what I had before I replaced the rear output bearing on the T-case and swapped the rear driveshaft (and the ear pressure that I now get again would correlate to that). Guess I'm going to pull the rear D/S again once all this snow melts off & see what happens then.

No apparent 'waaaaaah... wwaaaaaaaah....waaaaaah' noise, so I'm thinking that my rebuild of the rear diff addressed that at least!

 

[Bisho]

I've been meaning to come back to this thread!

So I went to COTR in October, waaaaaaah waaaaaah sound and all. Had an absolute blast. Blew my front diff, so hadn't been driving the truck much. But, can confirm my waaaaah sound was still present without the front diff spinning at all (no drive shaft, no hub flanges) on the drive back.

I put the rear up in the air, and with the tires spinning at 50mph, there was a weird rhythmic tapping sound you could hear with a stethoscope, and even without the stethoscope, the rear diff sounded *rough*. Sorta sounded like some rocks bouncing around in there. Again, when I changed the diff fluid a 1k miles ago when rebuilding the truck, the rear magnet had a lot of smoo on it - significantly more than usual. No chunks of teeth, just a whole bunch of paste.

Fast forward to now. I just finished rebuilding two 'new' diffs with ARB lockers, new bearings, and used 4.30 gears. Swapped them in over Christmas, and have done a couple drives since.

'Waaaaaaah.... Waaaaaaah' sound (I think) is gone, but haven't done much highway driving during break in. Hoping that we've solved this one though. If it's not solved, then it must be the T-case. I have a spare one of those too now, so if that's the case I can swap.

However... The 'ear pressure' thing is still definitely around. Not nearly as bad as it was when I started this thread, but still there at lower speeds/back roads. I'm highly suspicious of my AHC at this point - despite ALL suspension bushings being new OEM (front/rear upper and lower control arms, and upper/lower AHC 'shock' bushings), AHC globes and fluid being new, and neutral pressures being correct, the ride over small bumps/expansion joints/sealer joints in the road is TERRIBLE. Let me repeat that. IT IS TERRIBLE.

My 2003 Sequoia with a somewhat sporty Eibach suspension and ALL polyurethane bushings in the front rides SO MUCH BETTER. I know I'm shouting here, but I'm just trying to communicate how rough it is.

Big bumps/dips are absorbed super nice, but all the little stuff feels as if I'm riding on concrete (have I mentioned how bad it is?). I *believe* the overly stiff AHC is exciting resonance in the cabin (imagine hitting a drum with a stick) that's causing this problem. It's really bad driving down my gravel driveway (very bumpy), paved roads seem to vary, so I definitely think it's suspension related.
This is something I've noticed this entire time, but I've been focused on the higher speed highway type driving. There's a number of threads dating back a decade on this exact AHC problem with no resolution, so I've got my work cutout for myself to figure it out. We've currently got a ton of snow on the ground here in Indiana, so I need to undercoat the vehicle before I start driving again.

Thanks for following up!

I just got back from a long trip in the LX, and I’ve been thinking about your observations on your AHC. When I first got the LX I also had very rough ride over expansion joints and bumps, and it certainly wasn’t any better ride than my built 100. I changed the globes and fluid and got everything adjusted, and it was only marginally better. But…over time the ride has gotten downright smooth, and it is now night and day compared to the 100. It’s taken maybe 7k miles for me to say that, but it’s really nice now.

I can only speculate that the new fluid took time to clean out any gunk in the valving. I’ll probably do another flush this year to get it nice and clean. It was dark brown when I exchanged the original fluid.

 

[LJE]

I just got back from a long trip in the LX, and I’ve been thinking about your observations on your AHC. When I first got the LX I also had very rough ride over expansion joints and bumps, and it certainly wasn’t any better ride than my built 100. I changed the globes and fluid and got everything adjusted, and it was only marginally better. But…over time the ride has gotten downright smooth, and it is now night and day compared to the 100. It’s taken maybe 7k miles for me to say that, but it’s really nice now.

I can only speculate that the new fluid took time to clean out any gunk in the valving. I’ll probably do another flush this year to get it nice and clean. It was dark brown when I exchanged the original fluid.

Hmmmm, very interesting! My plan has to been to drive it for a while & see if I can better characterize it, so this would align with that pretty well!

 

[LJE]

Coming back around to this just to provide an update - I *think* my AHC suspension is slowly getting better. I don't have any explanation for why this would be the case, but it seems to be working. I bled the system multiple times after swapping globes & upper AHC bushings, but perhaps there was still air in the system somehow. Or, maybe there was gunk in the valving that's slowly getting cleaned out with the new fluid - again, your guess is as good as mine here.

I still get some low frequency noise that shouldn't be there I think, but, totally drivable now. I noticed my muffler feels a little crunchy & you can see where the metal is gone around the seam, so that may have enough internal rust that it's causing some noise. The noise is still speed dependent (not engine RPM dependent), so I wouldn't think the muffler would be contributing to it, but it's still on my watch list.

Also have a frame weight coming from @cruiserpatch just to rule that out, and because I do get resonance when sitting at an idle when in drive (but not in park). That frame weight is supposed to fix that issue specifically, so if it doesn't that'll further point to the muffler IMO.

I'll update this in the future if there's any big changes one way or the other, but, for the moment, I think we sorta got it taken care of.
At the end of the day I think it was a combo of a bad rear output bearing on my T-Case, u-joints on my drive shaft that weren't great, and overly (SUPER) stiff AHC suspension coupling all that right into the cabin, causing it to resonate right at the cabin air space's natural frequency (45-50ish Hz).

Thanks to everyone for following along & for all the suggestions!

 

[Bisho]

I don’t recall if you did engine mounts, but I just replaced mine and it solved vibration when stopped in drive.

 

[LJE]

I don’t recall if you did engine mounts, but I just replaced mine and it solved vibration when stopped in drive.

Those are brand new as well - both the left & right along with the transmission mount.

 

[RapidRob]

Those are brand new as well - both the left & right along with the transmission mount.

It's been a while since we talked about your body mounts. I mentioned that the mounts on my pampered LX appeared to show much different spacing
than yours between the big washer and the mount. Maybe take a close look at that as any contact without rubber between body and frame can make really
weird noises. Man, I wish something would magically solve this for you, you deserve the relief for all of your hard work.
But then what would you do? Still following and thinking.

 

[LJE]

It's been a while since we talked about your body mounts. I mentioned that the mounts on my pampered LX appeared to show much different spacing
than yours between the big washer and the mount. Maybe take a close look at that as any contact without rubber between body and frame can make really
weird noises. Man, I wish something would magically solve this for you, you deserve the relief for all of your hard work.
But then what would you do? Still following and thinking.

Would you be able to grab a photo of yours? If not, not worries - I probably should just compare to the new OEM ones I have sitting in a box, haha. Would be interesting to see what other 'aged' vehicles look like.

 

[RapidRob]

Yeah sure, I'll do it tomorrow, maybe hold a ruler up there so you can get a real feel for it.

 

[Bisho]

New driver side.

 

[Bisho]

Oops, you said body mount…

 

[RapidRob]

Would you be able to grab a photo of yours? If not, not worries - I probably should just compare to the new OEM ones I have sitting in a box, haha. Would be interesting to see what other 'aged' vehicles look like.

Here's a pic of the one right behind the right front wheel. I checked several others and they all were about 1/4 inch between the big washer and the tube that the bolt and rubber live in. This one was 5/16ths. Correct me if I'm wrong but I believe that space gets larger as the rubber collapses with age until metal touches metal. Hope this helps or at least takes this off your list.

 

[Rhetoric]

Perhaps this has been covered, but have you verified your ride comfort switch is working? My truck rides like a brick s***house in full sport unless its heavily loaded or Im towing.

I only ask because these switches are in the drink spill zone and get wrecked. Mine has corrosion in the traces preventing the illumination to work. I have also seen documented cases where the height control portion ceases to work due to this.

You should feel a range of plush float to near coil over harshness from full comfort to full sport.

 

[LJE]

Here's a pic of the one right behind the right front wheel. I checked several others and they all were about 1/4 inch between the big washer and the tube that the bolt and rubber live in. This one was 5/16ths. Correct me if I'm wrong but I believe that space gets larger as the rubber collapses with age until metal touches metal. Hope this helps or at least takes this off your list.

View attachment 3840498

Thank you for that! I'll check mine out & measure here soon.

Perhaps this has been covered, but have you verified your ride comfort switch is working? My truck rides like a brick s***house in full sport unless its heavily loaded or Im towing.

I only ask because these switches are in the drink spill zone and get wrecked. Mine has corrosion in the traces preventing the illumination to work. I have also seen documented cases where the height control portion ceases to work due to this.

You should feel a range of plush float to near coil over harshness from full comfort to full sport.

My switch is working (confirmed via techstream) - it does make a difference in the ride feel. Full comfort feels like you're floating... while hitting a whole bunch of little bumps still. Full sport feels as expected - very tight, at which point the little bumps are actually sorta less annoying because you'd expect that with how the rest of the ride is.
Front pressures are on the lower end of spec, rear pressures were originally 'high' with factory coils, now they're below spec with Kings KTR springs while I wait for my rear bumper. There wasn't really any ride quality change though when I swapped springs.

 

[MongooseGA]

I'll jump for joy if you can figure out the little bump harshness. Even in a perfectly sorted AHC truck it's still noticeable on tar snakes and little imperfections in the road. In my own truck I've just attributed it to E rated tires, but I know that's not the full story. I've seen a guy on here (maybe he's in this thread recently) who replaced all of his body mounts in an attempt to fix this, and at the end of the project, he was no better off.

 

[Rhetoric]

Well then. I think the Universe just decided to give you a fun puzzle of a truck because it knew you'd be providing a ton of data on this great forum!

 

[MongooseGA]

Well then. I think the Universe just decided to give you a fun puzzle of a truck because it knew you'd be providing a ton of data on this great forum!

It's a gift to all of us!

 

[Rhetoric]

It's a gift to all of us!

One man's insanity is another man's .

 

[LJE]

I'll jump for joy if you can figure out the little bump harshness. Even in a perfectly sorted AHC truck it's still noticeable on tar snakes and little imperfections in the road. In my own truck I've just attributed it to E rated tires, but I know that's not the full story. I've seen a guy on here (maybe he's in this thread recently) who replaced all of his body mounts in an attempt to fix this, and at the end of the project, he was no better off.

I'd really love to ride in an 'ideal' AHC truck to make sure I'm not insane, hahahha. That guy was in the thread that @fussychicken is pursuing. He went as far as to replace AHC with conventional suspension and still has it. Make me wonder if some of us are just crazier than others? Haha.

It certainly has been a headscratcher. On the other hand, it's been a great crash-course on super in-depth vehicle diagnostics & has given me a large amount of confidence that I can fix whatever goes wrong with my LX in the future. The only thing I haven't touched on this vehicle at this point is the transmission (knocks on wood) - I know that I can rebuild anything on this truck... because I've done it hahaha.