Painful low frequency drone/pressure in cabin

[LJE]

Dude... I'm so feeling this for you.

Assuming I make it to COTR, want me to hop in it and feel it out some? Maybe a second set of eyes (ears? Spidey senses? ) from someone with lots of miles in 100s may help?

Maybe it's your transmission. Seems to be going around

I appreciate that! If I don't have it sorted by COTR I'd certainly take a second set of ears!

I'm not convinced this trans (which, at the very least, has an aftermarket torque converter) is too long for this world IMO, which SUCKS too. I sometimes get a hard shudder right at like 38mph or 45mph that will instantly go away if I let off the gas for just a split second. It's pretty rare, but I don't like that at ALL. I did a full fluid exchange too and set per most current procedure... Oh well, I'll keep driving it till it explodes I guess, hahaha. As much as I've done and learned on this truck, not quite sure if I'm cut out to rebuild a transmission myself... But we'll see if that time comes, haha.

Ugh, dude! You're a beast for pushing this far. So much work for no resolution yet. I'm bout to dump this thread into chatgpt for other ideas cause I'm out of them lol

Hahaha - a beast, or just crazy...


Plan for later today is to pull the sliders off. This weird noise didn't start until I put them on - I've quadruple checked everything and nothing is rubbing, but it would be hilarious if I managed to turn the frame into a tuning fork with them. I think it has to be unrelated, but just in case.

One thing I noticed last night driving it after the wheel bearing replacement - this noise isn't super consistent in volume. Sometimes it seems like it gets better for just a second or two if I let off the throttle - sometimes it doesn't. Sometimes I can coast down a big hill at speed and still grt it full-volume. It's weird. The actual tone of the "wwhhhHOOOOOOMMmmm" also doesn't seem to change depending on speed (need to confirm), but the rate at which them come seems to speed up with road speed. Engine RPM has no effect. Pulling front driveshaft had no effect. Input bearing on 3rd member has no play.

Front bearings (which I've replaced) don't have any play when grabbed at the 12/6, but I have to pull my front wheels anyways to carefully adjust the pinch weld utilizing a precision artisanal adjustment tool, so I'll pop the C-clip and flanges off and make sure the preload is still set correctly.

And, going up to my in-laws tomorrow to throw it on the lift and run it to speed. The fact that I felt a wobble/shimmy in my seat when the rear axle was spinning at 45-60 mph on jackstands is burned into my brain - that surely can't be right.
But short of replacing the passanger side rear wheel bearing (at this point, why the heck not I guess...), I don't know what would be causing that. That was with the old road force balanced tires - I may get these much new Wildpeaks road force balanced too just in case I guess.

 

[lexuslandcruiser]

I've read every post in this thread, but forget - you did already swap wheels and tires with someone else and it had no effect, right?
And all bushings like LCA and UCAs, etc are new?

At this point, you've gone so deep I'm wondering if its something stupidly simple we just all are ruling out. I'm about to go study my LC and think on this more too lol

 

[MongooseGA]

At this point, you've gone so deep I'm wondering if its something stupidly simple we just all are ruling out. I'm about to go study my LC and think on this more too lol

Like a frame weight?

 

[LJE]

Like a frame weight?

That's it. Both your oil cap and your frame weight are disappearing into the beard at COTR.

Took the sliders off, no effect (as expected). Checked front wheel bearing preload - one was at 7lb, the other at 10lb. So a little light (which is interesting, I remember setting them both to 12 lb when I put the new bearings in). Bumped both sides back to 14lb or so, no change (as expect led - bearings felt tight.

I've read every post in this thread, but forget - you did already swap wheels and tires with someone else and it had no effect, right?
And all bushings like LCA and UCAs, etc are new?

At this point, you've gone so deep I'm wondering if its something stupidly simple we just all are ruling out. I'm about to go study my LC and think on this more too lol

I really should make a list of things I've done chasing this, but yeah, all new LCA/UCA bushings for both front and rear (all bushings short of body mounts are brand new OEM actually). I've got 'new' (6k mile takeoff from a Jeep) tires and rock warrior wheels. I also get the exact same noise when using the OEM wheels and Hankook dynapros that came with the vehicle.

 

[LJE]

Oh - here's a question. I assume everyone's front body mounts look like this? This is the one right behind the front passenger tire:

 

[MongooseGA]

Hmm... I'd have to lay eyes on mine to confirm.

 

[MongooseGA]

That's it. Both your oil cap and your frame weight are disappearing into the beard at COTR.

Everyone you meet: "Excuse me, my eyes are up here."

 

[Bisho]

That body mount is bad - there shouldn’t be a gap. I doubt it’s the problem, but you found another thing.

 

[LJE]

That body mount is bad - there shouldn’t be a gap. I doubt it’s the problem, but you found another thing.

I actually think it's OK - looking at a new mount (I have them all on-hand), the actual bushing looks the same. I think the bottom "washer" just has a weird step in it - see below Partsouq diagram.

I'd love someone to confirm though!

 

[RapidRob]

My cherry mall cruiser has about 3/8 inch gap there. If it's a lot more than that I'd be inclined to pull that nut off both sides, put a stack of washers or a spacer in there and take it for a drive. You've tried everything else right? Only for a test, you need a gap or your rubber mounts aren't doing anything.
Easy to do and maybe it'll tell you something.

 

[LJE]

My cherry mall cruiser has about 3/8 inch gap there. If it's a lot more than that I'd be inclined to pull that nut off both sides, put a stack of washers or a spacer in there and take it for a drive. You've tried everything else right? Only for a test, you need a gap or your rubber mounts aren't doing anything.
Easy to do and maybe it'll tell you something.

Thanks for the info! I'll measure tomorrow, but that's pretty close to where it's at I think.

 

[LJE]

OK, made some progress I guess.

Drove it up to the in laws - here's some things I confirmed on the drive:
1: vibration doesn't change in pitch with speed, only the rate at which it comes. The faster you go, the faster the 'pulses' come.
2: If you just 100% coast on a hill, vibration is still there. HOWEVER - if you give it just a little bit of throttle (like, you're taking the 'reverse load' off the drive train from going down the hill) then it 100% dissapears. If you give it too much throttle down a hill, it comes back. It's obviously present at all other times.

Got it up on a lift at the in-laws. Holy crap - when you're up in the air, you hit 45-60mph and you feel like the entire truck is going to come apart, haha.
Lots of vibration, but with a heavy "whhhHHOOOMMMmm" harmonic in it still. I realize that letting everything droop means the rear propshaft is riding at a weird angle at the rear diff input pinion, so it's not quite apples-to-apples, but the fact that the vibration I'm trying to chase down was still there tells me we were getting close.

The problem is.... 'close' is all we were able to get. The vibration is so low frequency the stethoscope doesn't transmit it. We listened to the rear wheel bearings, rear diff, transfer case, etc first just by spinning things by hand - nothing sounded bad. No super crunchy bearings or gears that we could tell.

We then repeated that with the truck in gear idling at 10mph or so, and still, everything sounded OK. Run it up to 60mph, and you can see the entire truct vibrating, but you just can't track down what it is!

We pulled the rear driveshaft, locked the CDL, and the vibrations all went away on the lift. Keep in mind, I've done that before and you definitely still get vibrations (different type, much more prominent at lower speeds) just driving around. The difference on a lift though is that your rear axle isn't spinning...

So, where does that leave us? Considering the rear propshaft is brand new, it seems either has to be the transfer case, or the rear diff. The fact that the transfer case was still spinning everything with the rear propshaft removed (and CDL locked) with no vibration would seem to point towards the direction of a bad rear differential - which seems like maybe the most rare failure of all on a LC/LX.

My father in-laws best guess is that there is a spot where there is bad wear on a couple of the gears in the rear diff - it takes several rotations for those gears to match back up in the exact same spot, hence the odd harmonic nature of the vibration.

Couple caveats to this:

1: this problem seemed like it started ~150 miles after I replaced the rear output bearing on the transfer case. That bearing still feels good, but I've got a spare new bearing & seal and I may just go ahead and swap it again to be sure. I spent $40 on those parts from Partsouq - that's way cheaper than anything on that diff...

#2: As mentioned, both the transfer case and transmission have been tampered with before. In my mind, someone screwing that up is more likely than a rear diff giving up the ghost at 255k miles, but again, I would have expected the front wheel-drive only test to then still exhibit *some* level of vibration.

EDIT: Just had a thought - transfer case has a differential as well (obviously). Wonder what happens if I lock this on a straight highway section? Quick test I guess...

 

[MongooseGA]

Just throwing out there, there's a flange and bearing on either end of the case as well. Before you get to the point of maybe opening the case, maybe you could try spinning the flange on the back side of the case to see what it's like on its own. You'll need to remove both shafts again.

You can also lift the truck by the axle and front control arms to mimic ride height.

 

[LJE]

Just throwing out there, there's a flange and bearing on either end of the case as well. Before you get to the point of maybe opening the case, maybe you could try spinning the flange on the back side of the case to see what it's like on its own. You'll need to remove both shafts again.

You can also lift the truck by the axle and front control arms to mimic ride height.

The output shaft on the T-case and the input pinion shaft on the rear diff both felt fine by hand (spinning with no propshaft in place obviously, and the T-case in neutral). That's not to say there's not an issue when they're both spinning at 40 rev/second with a load on them though.

Whats super, super, super weird is that on the drive home last night (1.5 hours) and the 30 minute drive I took this morning to confirm - the vibration has changed some.

You still occasionally get the "whhhHHOOOOMMmm", but in general you just get low-frequency rumbly-ness.
The ONLY thing we did yesterday beside listen was the pull and reinstall the rear propshaft. I forgot to make a witness mark on either end between the pinions and the propshaft, but wasn't too worried about it since it's nearly a brand new shaft (sub 200 miles). I don't understand how reindexing the position between the T-case flange and the rear diff could make any difference, but something has changed a little bit. Arguebly for the better.

Overall, it's way better than when this thread was started. It's annoying that it's not where it should be, but it's driveable now at least.

 

[MongooseGA]

I've never bothered marking the shafts relative to the flanges. As long a the shaft itself is in phase (if you slip the yoke all the way out, it needs to go back in exactly the same position).

 

[AARONTLC]

Like a frame weight?

Looks like J&J Auto Wrecking is parting out an 02 LX. Might be worth reaching out to them to eliminate this.

 

[zgfiredude]

Based on what you found here, I really feel like it's rear diff. Have you ever opened it up to look?

 

[LJE]

Based on what you found here, I really feel like it's rear diff. Have you ever opened it up to look?

I have not - I guess that involves draining it, pulling both rear axles, pulling the driveshaft, and popping the 3rd member out?

I remember one of the diffs or the T-case drain plug magnets had a little more shmoo on it than I was accustomed to seeing - problem is, I can't remember which one it was.

At this point I think I'm out of time before COTR - I leave for work travel this week, and will get back Friday. Figure it's probably best to not pull my rear axle apart within 7 days of an event.

 

[zgfiredude]

I have not - I guess that involves draining it, pulling both rear axles, pulling the driveshaft, and popping the 3rd member out?

I remember one of the diffs or the T-case drain plug magnets had a little more shmoo on it than I was accustomed to seeing - problem is, I can't remember which one it was.

At this point I think I'm out of time before COTR - I leave for work travel this week, and will get back Friday. Figure it's probably best to not pull my rear axle apart within 7 days of an event.

Agreed, I think I'd pull the rear cover and look around a bit prior to pulling axles and 3rd member. It is rotational (cyclical) in nature, I wonder about a chipped tooth or bad bearing in there or even too much play (could also look with rear shaft dropped)...and I suppose there is a chance of a bent axle, but that seems like a much lower likelihood.

You have come so far and addressed so many possibilities the end simply has to be close!!

 

[LJE]

Agreed, I think I'd pull the rear cover and look around a bit prior to pulling axles and 3rd member. It is rotational (cyclical) in nature, I wonder about a chipped tooth or bad bearing in there or even too much play (could also look with rear shaft dropped)...and I suppose there is a chance of a bent axle, but that seems like a much lower likelihood.

You have come so far and addressed so many possibilities the end simply has to be close!!

There's unfortunately no rear cover - only way to get a look at the gears is to pull the 3rd member - other than borescoping through a diff oil fill or drain plug I guess.