Front end mystery sound. Maybe transmission?

Can/will an AT make a sound like a resonating glass bowl/bell? Or pitchfork? I'm getting this new sound very prominently at 28 mph, when the throttle is open. If i'm coasting I don't hear it. But if I'm using throttle to sustain 28mph, it's constant. It disappears above and below 28mph. But when it's hot out, it will appear at higher speeds also at higher frequency's. it doesn't move up continuously in pitch, it just disappears and reappears at different points and pitches. It's definitely the sound of hollow metal resonating, mostly likely by a spinning part rubbing on it. (Like rubbing your finger on a crystal glass rim).

It appeared after getting my truck re-geared. Took it back to the shop and though they couldn't see how it could relate to the front differential, they took out the axles and inspected everything. Looked good. But sound is still there.

It doesn't seem like the front diff., because I have ADD hubs and the spider gears are always moving. This sound only appears with throttle, but not when coasting.

The day before I had the re-gearing done, I put a bottle of Lubegard black in my trans, at the suggestion of a trans shop, in hopes it would help what I suspect is a dying transmission. It seemed to exacerbate my trans problems so I did a few drain and fills to get it out. Now I have this noise and don't know if I should still be concerned it's my front diff., or perhaps its the trans getting ready to take a sh*t.

I hate these atypical noises that no one has ever heard/experienced.

 

I would start by eliminating everything that spins on the front of the motor . Pop the belts off and run the truck for a short period in time and listen for noises .
Is the noise still there in park while revving the engine ?
Once the belts are removed , rev the engine to verify and confirm that you dont have an issue with the many rotating pulleys on the front of the engine .
Noises are difficult to diagnose over a keyboard . Any chance of making a video ?

 

All your intake tube/ducting still clamped tight and sealed?

Partial throttle can sound pretty hollow or ringing if that stuff is loose or you have a open gap somewhere.

28 mph is just cracking the blades on the TB, so it might just be as simple as the buildup of gunk on those blades and that area.

A easy check is the only reason I put that up. I have a sneaky feeling that's not the problem.

A short video would be great if you can.

 

The sound is definitely coming up through the floor boards and not from the engine compartment. Even the mechanic at the gear shop admitted it sounded as if coming from the vicinity of the front carrier.

The transmission is also right in that vicinity, and since I only hear this sound on throttle, I suspect that.

28mph is just the speed at which it's most prominent, loudest, and noticeable. It happens at others but is less audible.

I'm an audio engineer/musician by trade. I work with sounds/timbres all day long every day. The sound is resonating metal. 28 mph must be the speed at which the moving part that is causing it is moving/rubbing at the correct speed to amplify the metal part's resonant frequency.

I'll try to make a video, but its on the passenger's side and I suspect road noise and such may drown it out.

 

If the issue is sound resonance , you should be able to reproduce it at the same rpm while you are parked in your driveway

 

Yeah, but in my driveway, I'll be in neutral. And the truck won't be under load. I'll try it, but if it was rpm specific, I would expect the sound to appear at different speeds around 28 mph, depending on the load. But it's consistently at the same speed, whether the road is inclined or not, or with different weights in the bed.

I took a pretty decent video of it. I'll upload it later when I'm at my computer. Hopefully that will clarify.

 

http://youtu.be/TZuvegTG5a4
It happens twice in this video, once for a longer time and once for a short time.

The longer time was when I was able to hold it steady right at the speed at which it happens. The shorter time is when I accelerated through the target speed. Just 1 mph above the speed and it drops out.

On the way home, I tried different speeds with the same rpm, and none of them produced it. It only happened at 28 mph.

I also tried 28mph at different rpms and it always happened regardless of the rpm.

Again, it only happens while accelerating or keeping the steady speed. Coasting or decelerating does not produce it.

Furthermore, on hot days, after driving for some time, it will appear at different speeds and in different frequencies. Sometimes there will be 2 or more resonating together and sounding quite eerie. Still, the pitch that appears at 28mph is always the loudest. I imagine the other sounds to be harmonic resonances of the principal pitch.

 

Where'd everybody go? I thought the video would help.

 

What rpm does the noise show up at ?
I listened to the video but was unable to determine the sound
If this is a resonance issue , you can reproduce this in your driveway under load .
Scroll to page 20 and perform a stalltest http://fjcruiser-club.com/docs/RM/A7...0Transaxle.pdf

What you are looking for when you perform a stall test is trying to re-create the noise/ resonance at the same rpm the noise occurs when you are driving the truck . In your case the noise or resonance is most noticeable at 28 mph . Read your tachometer at 28 mph then do a quick stall test at the same rpm in your driveway . Does the resonance happen during the stall test at the same rpm ?
When you re-geared , did you raise the differential ratio or did you leave the gearing factory ?

 

I think I hear it in the video, but not quite sure.

Did the shop happen to get the front rubber cushioned diff housing mounts a bit to tight?. If they regeared the front and had to remove that housing, they might have crushed those cushions to the point of zero sound insulation during re-install.

 

^^^^^^ I agree with Mod . Something is now metal on metal

 

Haha, we got scared & ran off. I could faintly hear something, But I for one wouldn't put ANY kind of repair in a can into the A340F trans , for as good as they can be (if maintenanced on time & regularily, every 30-35K IIRC) they are hands down THE fussiest transmissions I've ever encountered & that trans shop shouldn't have recommended you doing it, With this coming to light I'd say your trans is NOW on the fast track to failure, from the guys I know who work on them from time to time they tell me that the only thing that kills them is getting hot & the bigger culprit is dirty fluid with a lot of transmission "flash" contamination, which is probably clogging or slowing the flow of cooled fluid, what made you think your trans was going out anyway ? Is there any or has there been any unusually hard upshifts? , thats how I found out about the frailties of a less than perfect maint. fluid change out, these fuckers gotta have it done right & regular.. The only warning I got was 3 or 4 hard upshifts the day before it went out completely....you dont EVEN want to know how much to rebuild, I hit up a wrecking yard for another & found out that $1000 was cheap for these....

 

The sound appears from 0:07 - 0:10, and then again very shortly at 0:16. It's definitely metal on metal. You may need headphones if your computer speakers are not very accurate, but you can definitely hear it in the vid.

It doesn't seem rpm specific. It happens at 28 mph whether the rpms are 1750 or 2000 or 2100. And attaining those rpms at different speeds does not really produce it.


Besides general sluggishness under heavy load, the first symptom my trans presented was a jerk when letting off the gas pedal too quickly during acceleration (during stop and go traffic). It starts out small and gets worse over extended driving in traffic, until it shakes the whole truck. It also does it if I hit the gas too quickly. I can more or less avoid it by easing on and off the pedal, until it's really bad. Then I can only dampen it. I've always figured it was torque converter lock-up, but it may just be slipping in the trans.

The trans also gets tired in the heat after driving some time. It loses its pick-up. Lots of revving in the engine but its not translating to the driveshaft. Occasionally, I will feel it search a second or so for a gear.

The trans is loud. Louder than the one in my old Prerunner. Not just vibrations, but different whines.

My truck has always seemed sluggish under load. On flat land pick-up is okay, but on hills it bogs down. I re-geared to 4.88 and am running 33's. I can't get over 60mph on a mountain pass. Even then, the rpms are 3000+ and the truck is maxed out. My old pre runner with 4.10's and 30" tires cooked over mountain passes.

I've done a thousand drain and fills of the trans. I first used Dexron III that I got from Toyota. I dropped the pan and cleaned it out. 6 months later, I switched all the fluids in my truck over to Redline synthetic. I put their D4 AT fluid in the trans. I noticed an immediate improvement to engine pick-up. However, the jerking I described above began getting worse. I have also lost about 5mpg's. The trans shop told me to add the lubegard black, since I was running synthetic and not toyota specific fluid. It made the above problems worse in just 60 miles. So, I did 2 drain and fills to get as much of it out. I'm still running Redline.

I'm currently looking around for a used trans. However, I'd like to figure out what this new noise is, so I know if I should be back at the gear shop or not. It did start right after re-gearing and is coming from the are of the front diff. But maybe re-gearing changed the resistance on the trans, bringing out a new problem??

 

http://www.tacomaworld.com/forum/technical-chat/325531-aisn-warner-340-series-transmissions.html

http://www.sonnax.com/parts/2764

 

Well, back to the main question. Based on the video and my description does this sound like something the trans is doing or is it some how possible it's the front diff?

On the way home I found an inclined road that pretty much let me coast at 28 mph. keeping that speed by gravity, there was no noise. but if i even tapped the pedal it would appear and remain until i let off the pedal. immediately gone. tap the pedal and it's back. Only happens at 28mph.

So, it's a metal on metal sound that only appears at a given speed but also only with throttle. It's not dependent on rpm, but on speed. It has to have at least some throttle to appear, but the rpm doesn't matter. It emanates from the floorboard by the trans and front carrier. It appeared after a re-gear and a trans additive that was not welcomed. A specific speed with throttle coming from front end.

Heat will cause it to appear at different speeds in different frequencies but always most prominent at 28mph.

 

You mentioned re gearing , can I ask the dumb question ?? Did the front get re geared to match the rear ?? I know even if in 2wd with the ADD shift on the fly thing shit is still turning in front I'd think.... too bad its not a loud distinctive howling then it'd be easy diagnosis , pinion bearing... only reason i mention it is your reference to the noise being at a certain point.. ...

In Ca. did you know that the A340F (& the E series too) is so embedded with the emissions that just finding a used A340F wasn't enough, it had to be a CA. trans or it wouldn't pass smog

 

Yes, the front matches the rear. It's true, even in 2wd the spider gears are turning with ADD. We thought about that. But if it was them making the noise, I would expect to hear it even while coasting, since they're still turning then. But this ONLY happens when I hit the throttle. That's what led me to suspect trans.

The guy at the gear shop was scratching his head. He spent a few hours going over everything, but he couldn't see how it could relate to what he did.

If it was a pinion bearing, wouldn't it change with the speed continuously? And wouldn't I have to be in 4wd to have it engaged? I wish I had manual hubs so I could unlock them and rule out the diff all together.

What it sounds like to me is a squeaky silo vent fan.

 

Well I was thinking the rear pinion really & you'll hear some noise while driving usually its when decelerating/letting off the gas is when shit gets real & the patented howling takes place, mine pretty much lost all the preload & i could rotate the pinion almost 1.25" out of the diff by hand, no mystery to troubleshoot there..haha

& you've already covered the carrier IIRC...

 

And gearcruncher, the pdf with the stall test says to hook up the intelligent tester to the can vim. I don't know what that is. I also don't have wheel chocks, so can't do the test just yet. The standard value given in the pdf is for an FJ. Is it the same for a Tacoma?

 

Nothing that's gone bad on this truck has been typical. And a lot has gone bad. Most I haven't even fixed yet.