Painful low frequency drone/pressure in cabin

[RapidRob]

if I was 500 miles closer I would insist on driving up there and swapping wheels/tires with you for a test drive.
Surely someone close could be convinced to do this. I'd just like to see it completely debunked.

 

[LJE]

if I was 500 miles closer I would insist on driving up there and swapping wheels/tires with you for a test drive.
Surely someone close could be convinced to do this. I'd just like to see it completely debunked.

Haha I appreciate that! I've been looking on ye Olde FB Marketplace at some other stock wheels with OK tires - may have to grab a set if my below reasoning doesn't work out...


NERD ALERT: Let's do some math. I'm sorry to subject you to this, but my poor wife needs a reprieve from my ramblings.

The noise is worst around 50 mph. But what does that mean in terms of mechanical things that we have spinning? Let's figure it out:

50 mph * 5280 ft/mile = 264000 ft/hour.

(264000 ft/hour / 60 min/hour) / (60 seconds/min) = 73.33 ft/second.

So that means my tires have to cover a linear distance of 73.33 ft every second at 50 mph.

These tires are (more or less) 30", which is 2.5 ft. Circumference is just diameter*pi, so the tire circumference is 7.85 ft.

So, the tires cover 7.85 ft per revolution. That means in order to cover 73.33 feet a second, they have to spin at (3.33 ft/second/(7.85 ft/revolution) = 9.34 revolutions per second (RPS).

So that means that the front tires & CV axles are spinning at 9.34 RPM - which is probably too low to excite the sort of resonance I'm experiencing - but what about that front driveshaft? Well, the front diff in an 2005 LX has a 4.10 gear reduction, which means that at 50 mph, that front drive shaft is spinning at 4.10 * 9.34 RPS... which is, wait for it....

... equal to 38.3 RPS. That dang front drive shaft is spinning at the exact frequency (give or take some fudging on exact tire size) that I'm getting pressure resonance inside of the cabin. That's a little suspicious.

Oh - and remember how I mentioned in the video (at least, I think I did) that at 65 - 70ish it got better because the frequency of the pressure peak shifted to 50+ hertz? You guessed it, the math works out there too. At 65-70 mph my driveshafts are spinning at 50ish hz frequency.

Hmmm....

As mentioned, I've already tried pulling the rear drive shaft. Tomorrow morning hopefully will tell us more when I pull the front.

 

[rbrave]

Editing to mention we posted at the same time! Checking your math with mine now…

“Sound goes away entirely in the middle row, comes back in the third row.” Almost like…when you are closest to the tires?

Two other random thoughts on sound:

1) Concept of sound waves. You observe where the sound starts and stops, and perhaps you can estimate where it’s coming from based on frequency. The period of 40hz is 0.025 seconds, with a 28ft wavelength. You also showed an 80hz peak, which is half that. The reason you are getting so frustrated finding the sound is because it’s next to impossible to spatially identify low frequencies like this. It’s why you have lots of small speakers in a sound system for vocal ranges, and one giant speaker for low frequencies. So - your sound is happening in the first and third row, which are how far apart?

2) Super long shot but hadn’t seen this anywhere. LX’s apparently have a microphone in the back of the cabin for calibrating the sound system? How funny would it be if there’s something wrong with your stereo after all this… ‘98 LC over here, I just listened to a cassette tape on my drive home.

 

[rbrave]

at 50 mph, that front drive shaft is spinning at 4.10 * 9.34 RPM... which is, wait for it … 38.3

HAHA! Your units are per second (RPS) and 1/38.3 is 0.026 seconds. I think you found it.

 

[LJE]

HAHA! Your units are per second (RPS) and 1/38.3 is 0.026 seconds. I think you found it.

Whoops, you're right! That's what I get for typing out on my phone. Who needs units anyways?!?

(I'm joking - improper accounting for units is how we crash things into Mars...)

 

[FamilyCamper]

@LJE first, Ive come to love you from this engine swap bonding and your awesome revival of the LX. I appreciate all your advice. second, this thread hurts my head so (hears) my advice. Turn up music, let it rock. At the same time I love that this forum has every type of person and can offer advice from "tighten till you cant nomore" to "specific torque range using this specific grease and this specific adhesive on the threads"

 

[Patron100LC]

here’s another theory.
Since the noise goes away in the middle seat, that means someone was sitting there to confirm.
Can it be that the seat vibrates, and goes away when someone sits there?

 

[LJE]

here’s another theory.
Since the noise goes away in the middle seat, that means someone was sitting there to confirm.
Can it be that the seat vibrates, and goes away when someone sits there?

The noise only goes away to the person that's sitting there in the middle - the person driving still hears it clearly.



So - pulled the front driveshaft today.... no change! What in the world?!?
Then, went ahead & reinstalled the front driveshaft, and pulled the rear driveshaft again to make sure I hadn't bodged something upon reinstall from last time. When I pulled the rear driveshaft originally, it was very early on in this troubleshooting process - prior to getting the tires roadforce balanced, prior to regluing hood + roof, etc. I did notice upon closer inspection that there is a small dent in it, so that's slightly suspicious to me.
Went for a test drive again without the rear driveshaft... and wait a minute, things are different now!

Overall an improvement. At 45+ MPH, it's "not that bad", including the 50ish MPH zone where it was torture before. However - I get more noise/ear pressure down at lower speeds, and there is now noticeable vibrations corresponding to the feelings of pressure/noise! The peak sorta shifts between 45-55hz on the spectrum analyzer (frequency doesn't seem speed dependent), but holy crap, it now definitely seems exactly what I would think tire vibrations would feel and sound like.
I was even able to excite the truck into a severe vibration a couple of times - once at 30 mph, the other at 38 mph. The shaking would go away as soon as I accelerated out of it, and wouldn't happen again if I tried, but it definitely was there. Both my wife and myself will swear that these vibrations were not present prior to pulling the rear drive shaft!

So - here's my current hypothesis (subject to change as soon as I debunk it like the previous couple dozen...): These tires are indeed inducing a vibration into the driveline. With the rear driveshaft in place, it may have been acting somewhat of an damper that was absorbing a lot of the lower-speed vibrations, until that 50 mph / 40 revolutions per second zone where it would hit some sort of resonance.
When I pulled the rear driveshaft originally (prior to regluing the hood/roof & roadforce balancing the tires), there was still enough other things resonating the cabin that it didn't make much of a difference. Now, without the rear driveshaft in place to act as a damper as low speeds, the vibration from the tires is very noticeable.

Thoughts? In my mind I still have some lingering questions I guess:

1. What about that small dent in the rear driveshaft? Obviously without it being in the truck it's not causing the problems now, but I'm concerned that might still be a contributing factor down the road.
2. Rear wheel bearings? They don't seem to be making bad wheel bearing noises, it doesn't get worse going around corners (either direction), and the axle housing isn't hot on either side after driving.
3. Output bearing on the transfer case/input bearing on the rear diff? Neither seem to have any 'slop' in them though.

Guess I have to accelerate my plan to get new tires... Looking for something in the 33" range (stock AHC), probably going to have to buy some sort of 17" wheel (was trying to hold out for a set of rock warriors near me...). Any recommendations?

 

[rbrave]

Nomad gets my asthetics vote for a 17” wheel:

What have you done to your 100 Series this week? - https://forum.ih8mud.com/threads/what-have-you-done-to-your-100-series-this-week.609679/post-15618526

 

[MongooseGA]

Output shaft on rear diff could be bent. This can, to an extent, be soaked by up the U-joints, but it can also shorten the life of those joints.

You don't have a buddy with a 5.7 Tundra to trade wheels/tires with for a few hours? I know data points toward tires, but my spidey-senses just don't tell me tires. I'd hate for you to buy a new set just to find out you have the same issue (unless you're in need of rubber anyway).

Drive out here to Atlanta, you can throw on my Michelins. The family of birds in your beard is also welcome.

 

[LJE]

Output shaft on rear diff could be bent. This can, to an extent, be soaked by up the U-joints, but it can also shorten the life of those joints.

You don't have a buddy with a 5.7 Tundra to trade wheels/tires with for a few hours? I know data points toward tires, but my spidey-senses just don't tell me tires. I'd hate for you to buy a new set just to find out you have the same issue (unless you're in need of rubber anyway).

Drive out here to Atlanta, you can throw on my Michelins. The family of birds in your beard is also welcome.

Hmmm - I would suspect if that were the case that the vibration frequencies would change more notciably with speed - what I'm experiencing now is pretty consistent across the low speed range. I'm assuming the tires are creating some weird wide spectrum vibration, but I certainly could be wrong there.
For what it's worth, the transfer case lever is actually way less vibrate-y now than it was prior to pulling the rear D/S. Prior to removing the shaft, if you put your hand on it while you were in the 50mph death zone, the shake was VERY noticable on the TC shift lever.
But, I guess I could put jack stands under the rear and spin the tires to see if the diff input shaft wobbles at all? I just would think it would take a heck of an impact to bend that.

Do I "need" new tires? No, these Hankooks have quite a bit of tread left on them. Do I want to show up to Cruisers on the Rocks in OCT with Hankooks? Also no...
Tires/wheels have been on the list, just wanted everything sorted out 100% before dropping close to 3K on tires/wheels/lugnuts/spacers (if needed) etc. But, if that's what it takes to solve this...

And unfortunately I don't know a single person with a 5.7 Tundra or Sequoia. I've got a 4.7L (1st gen) Sequoia, my dad has a first gen Tundra, and my younger brother has a V8 4th gen 4runner (the 2UZ runs strong in our family apparently, hahaha). But those are all 6 lug wheels.
I appreciate the offer, but Atlanta is a little more than just a stone's throw from south-central Indiana, hahah!

 

[MongooseGA]

I hope you get it sorted by COTR. I'll see you there!

 

[Zuberg]

17" wheels, I went with FN wheels 5 star. Great offset (no spacers needed) and good weight. Simple, clean look.

 

[Bisho]

If your driveshaft is dented, there is a chance its bent and out of balance. You may want to find a place that rebuilds them and have it checked. While you have the truck in the air, check that your rear wheels don't have any wobble, indicating a bent axle.

 

[LJE]

If your driveshaft is dented, there is a chance its bent and out of balance. You may want to find a place that rebuilds them and have it checked. While you have the truck in the air, check that your rear wheels don't have any wobble, indicating a bent axle.

So here's something interesting - when I went to spin my rear tires, I noticed my driver side rear tire definitely has a low spot - check out the video below. I added in the white boxes just as a reference point. You can see everytime that white mark (added by me) on the tire comes around, that it's about the lowest spot on the tire. It was enough to notice by eye. The wheel itself is tracking pretty dang concentric though.



The passanger side rear doesn't have that same type of low spot, but who knows about the two front tires?

I tried swapping in the spare tire to both the rear tire positions with no effect, but if the front tires have low (or flat...) spots too, that could explain why it didn't take care of the vibration.

Or, maybe that's normal with tires? My gut tells me it's not though...

One thing I REALLY noticed tonight is that road condition/flatness makes a HUGE difference. If you have a very flat/smooth road, it's not bad. A less-flat road? Ouch, my ears. Gravel roads? Fuggitaboutit.

 

[RapidRob]

Man, I keep coming back to the tires. Tires should be absolutely round.
BUT, If your issue is the same or worse on gravel roads, It's unlikely the tires.
Just had a thought though, how about running some radically high or low pressures in the tires for a test session?

 

[LJE]

Man, I keep coming back to the tires. Tires should be absolutely round.
BUT, If your issue is the same or worse on gravel roads, It's unlikely the tires.
Just had a thought though, how about running some radically high or low pressures in the tires for a test session?

Oh, that's not a terrible idea at all. I'll drop the PSI tomorrow morning and go for a spin!

Also, the fact that I can now (sometimes) get the entire vehicle to shake at what seems like it should be tire rotation frequency points me towards them too... That's definitely new since pulling the rear D/S.

 

[RapidRob]

So, you tried some lower pressures and the tires rolled off the rims and you crashed down a ravine and haven't been found yet.
I feel so guilty.
If that's not the case, let us know how it went, please. I'd sure like to know what finally solves this.
My next dangerous thing to try would be to get it going at it's worst and just turn the key off,
At your own risk!! But that would rule out an exhaust drone, they can be very hard to diagnose.
Good luck and be careful of your surroundings if you try this.

 

[LJE]

So, you tried some lower pressures and the tires rolled off the rims and you crashed down a ravine and haven't been found yet.
I feel so guilty.
If that's not the case, let us know how it went, please. I'd sure like to know what finally solves this.
My next dangerous thing to try would be to get it going at it's worst and just turn the key off,
At your own risk!! But that would rule out an exhaust drone, they can be very hard to diagnose.
Good luck and be careful of your surroundings if you try this.

Hahhaha sorry - not dead! Just out of town on work travel. I tried lowering to 20 PSI, not much change. Bumped up to 40 PSI, maybe slightly better, but it's very subjective. I also had re-installed my rear driveshaft when I tried the 40 PSI. It's interesting - now that I know what to 'look' (really, feel) for, I can feel the lower speed vibrations with the driveshaft in place, but they're not nearly as prominent as with it removed. Still, being able to actually feel vibrations helps point towards tires. I quadruple-checked that everything in my suspension is tight, and it's all good.

I've got a lead on some Rock Warrior rims & nearly new Falken Wildpeaks (take offs from a Jeep), both over in Ohio. Going to take the Sequoia on a 8 hour (total) road trip Saturday to get the wheels and tires. I've got some 1" BORA spacers on the way as well to let me use the Rock Warriors on my LX. That will (hopefully) put this issue to rest, but at the very least it will rule out tires.

 

[MongooseGA]

My next dangerous thing to try would be to get it going at it's worst and just turn the key off,
At your own risk!! But that would rule out an exhaust drone, they can be very hard to diagnose.

Actually, this is a good idea to rule out and engine running sources. Not really a big deal, either. I've done it many times- just bump her in neutral and make sure you've got a decent, low traffic straight section ahead.