Solved: Drone @ 2400-2800 rpm - frame to body contact

Joined
Aug 13, 2013
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327
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Chandler AZ
I recently changed tires on our hundy from Toyo ATIIs to Michelin LTX MS2 to quieten the ride down a bit for some long trips we have coming up, and have discovered that we have a pronounced droning noise at 2500 rpm - which is unfortunately right at our cruising speed of ~ 70 mph. Drone starts around 2400 rpm and then clears up after 2800 rpm.

01 LX 470, 285/75R16, 132k miles

Diagnosis:
- happens in all gears (except maybe reverse? :hmm:) and all speeds
- must be under load/in-drive. I don't notice it in P/N, or standing in front of an open hood
- A/C on/off doesn't make a difference
- if engine is turning at 2500 rpm and in 4th (its an 01), and I turn off OD, it shifts down to third, engine goes up to 3300 rpm and sounds and feels quieter. Speed hasn't changed and drive train is still doing the same work - at least down stream of the AT.

Things I've tried:
- re-installed the flux-capacitor ("what is this") with no change.
- cleaned throttle plate, MAF, checked over the intake assembly and we have a new air filter - no change.

Other ideas:
- exhaust? Muffler has some (small) dents from rocks etc in it which have been there a while, but otherwise exhaust system seems good.
- pulleys and idlers on the accessory belt? I think if there was an issue here, it wouldn't need to be in gear and under load?
- wheels are heavy. 285/75R16 are 10 ply and heavy tires. Is the AT complaining about the extra work? I've tried to deflate them a bunch to get the wheel diameter to ground closer to OEM - no difference. Vehicle is heavy; front & rear bumpers, sliders, winch and 16 gal aux tank.
- transmission - is 2500 rpm around a shift point? ATF is good. Level looks good as near as I can tell - though I have hard time with that dipstick. Its either dry (when off) or thoroughly covered once one and I've shifted through all the gears.
- spark plugs and coil packs. 132k miles is about when we are supposed to replace plugs. No error codes. Idle speed in Neutral with AC off is perfect, but in park its low (600 rpm sometimes - AC on).

Other ideas? Best guess is the muffler right now, but that's some work for just trial and error. Turn up stereo and carry-on?

Will appreciate the MUD collective wisdom.
:cheers:
 
Joined
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Decatur,Tx
There is a shift point between 3-4th gear @ 2k-3k rpms on the A343F. You will find that more added weight and a larger overall tire will cause more road noise. A through suspension look and handling test will find the root source. let us know what you find.
 
Joined
Jun 23, 2016
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Wyoming MI
To rule out the engine, run her up to ~70 with no traffic, straight expressway out of the city is best, s*** to neutral, kill the engine. Listen for the drone, is it gone?

The steering wheel will NOT lock doing this, you will have manual brakes and steering.
Start it back up, now your power steering and brakes are back.
 
Joined
Aug 13, 2013
Messages
327
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Chandler AZ
Thanks for the input.
I don't think I need to do the at-speed engine off test (as fun as that would be) because if I take my foot off the accelerator the noise goes away.

Today I removed the front drive shaft and tried rear wheel drive only mode. No change. I do like the RWD only mode though. Need to see about getting some front wheel locks and system. @LandCruiserPhil
 
Joined
Aug 13, 2013
Messages
327
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Chandler AZ
Latest tests and results:
- Since I am in RWD only mode, it gives me the option to UNLOCK the CDL and rev the engine and exercise the transmission and most of transfer case without actually turning the wheels. I tried this and the drone is not there, which leads me to believe that it is not transmission or transfer case related.
- At 70 mph and 2500 rpm I can slip the transmission into neutral and the drone goes away - still at the same 2500 rpm and wheels still turning and drive shafts are turning etc. No Drone. Everything is turning as normal, except the engine and transmission are not connected to the load (wheels on road).

So at this point I am reasonably confident that its not directly drivetrain issue, such as wheel bearings, unbalanced drive shaft, transfer case or transmission. I am also confident its not the engine itself, w.r.t. accessory or timing belts, pulleys, fan etc.

The noise really seems like its air/aspiration related, either intake or exhaust.

- I removed the air filter and went for a drive. No change, drone still present - so not air intake related, ... which leaves: exhaust!?

What do you think?
01 LX with 132k miles, 16 years old, AZ truck its whole life.

Do mufflers age somewhat independently of miles? I didn't think 132k miles on the same muffler would be an issue, but maybe it is? Or maybe its just old? Exhaust system is still all stock. This is an 01 where there are the crack issues that occur in the manifold but I don't hear the tick when cold and I believe it seals up and goes away as it heats up.

I could see that the performance of the exhaust system and the back pressure to the engine creates the noise and how it can be load dependent. The load on the crank shaft is different when connected to the wheels and road, hence the connection to the exhaust system.

Time to go check out this thread for muffler replacement options.
Got Direct Fit Muffler Replacement Experience
 
Joined
Jun 23, 2016
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2,505
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Wyoming MI
Some mufflers have a matting inside them to help make them quieter, I suppose it is possible for that matting to deteriorate over time, in that case miles wouldnt matter, just age obviously.
I have no idea if these mufflers have that matting or not.
 
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Yes. Thats exactly what I mean, again I have no idea if these mufflers have any. But some mufflers do.
 
Joined
Aug 31, 2014
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New Orleans, Louisiana
Latest tests and results:
- Since I am in RWD only mode, it gives me the option to UNLOCK the CDL and rev the engine and exercise the transmission and most of transfer case without actually turning the wheels. I tried this and the drone is not there, which leads me to believe that it is not transmission or transfer case related.
- At 70 mph and 2500 rpm I can slip the transmission into neutral and the drone goes away - still at the same 2500 rpm and wheels still turning and drive shafts are turning etc. No Drone. Everything is turning as normal, except the engine and transmission are not connected to the load (wheels on road).
This would leave me to believe further that it is a rear u-joint. It isn't in the front moving parts, it isn't the tranny or t-case, BUT it could be when you are applying a load to the rear drive shaft. I would just try and put the front driveshaft on and drop the rear one, lock the CDL and go for a drive as a FWD Hundy. That will eliminate everything for sure, and it is reasonably easy to do (8 bolts). I am only sticking with this because I chased a huuummm around for a while thinking it was a wheel bearing (expensive nope), cv shafts, etc. It ended up being a rear u-joint.
 
Joined
Aug 13, 2013
Messages
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Chandler AZ
Thank you! I have to hold off on the FWD hundy for a bit...waiting for replacement bolts for the front shaft. I had to cut two to get the front shaft off. Some of them were pretty rounded too so I ordered a full set of 8. 4 from LA and 4 from Baltimore....Toyota had to search around a bit. It could be the rear shaft, but it really sounds like something in the front.

Tonight I tried again with the intake...it definitely sounds like its coming from there somewhere. I removed the duct in the passenger wheel well and checked it out. Went for a drive without it and while it sounded more throaty my drone was still there between 2400 and 2800 rpm.

I have also ordered a muffler and have neighbour with the right skills to install it. Will probably try that at the end of the week. If THAT doesn't work, then I am going to have to just chalk this up to the larger tires/heavier wheels causing additional strain at the top of the power band where the 3-4th shift is, and where there isn't a 4th to 5th on my 01!

Could it be that upping the wheel size puts just enough extra torque on the drive shaft that there's more groan from the engine? Is it just a bad spot. If I had a set of 275/70R16's I'd throw them on there in a flash to see.
 
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Messages
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Chandler AZ
Well....it wasn't the muffler...put a new one on (Bosal) and it made no difference - not even a little bit. So...when I get back in a week I will take it in to Toyota and ask them to service the rear drive shaft. I noted in the Service Manual that the "spider bearings" are not re-usable.

I am puzzled why the rear drive shaft issue would manifest as a sound from the front though...maybe its transmitted back up the drive train? What other damage is it causing? What is actually making the noise, the bearings in the spiders chattering? I have lubed and re-lubed the spider and slip yolk. Another question: whats the best way to do this so that grease that is pushed out does not splatter all over the underside where the U-joint is? Such a mess.

I did put the front drive shaft back on too, since the replacement bolts arrived. Good to have an AWD machine again.
 
Joined
Jun 23, 2016
Messages
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Wyoming MI
Well....it wasn't the muffler...put a new one on (Bosal) and it made no difference - not even a little bit. So...when I get back in a week I will take it in to Toyota and ask them to service the rear drive shaft. I noted in the Service Manual that the "spider bearings" are not re-usable.

I am puzzled why the rear drive shaft issue would manifest as a sound from the front though...maybe its transmitted back up the drive train? What other damage is it causing? What is actually making the noise, the bearings in the spiders chattering? I have lubed and re-lubed the spider and slip yolk. Another question: whats the best way to do this so that grease that is pushed out does not splatter all over the underside where the U-joint is? Such a mess.

I did put the front drive shaft back on too, since the replacement bolts arrived. Good to have an AWD machine again.
Sounds can telescope through connected parts, it's like playing telephone with Solo cups and string.
To keep the grease from flying everywhere, you need to wipe off the excess. I let it fly, it's rust protection. Lol
What other harm can it be causing? Who knows. Most likely none.
 
Joined
Aug 13, 2013
Messages
327
Location
Chandler AZ
Found it! :)

Took the LX into Camelback Toyota and asked them to check out the rear drive shaft, replace the spider bearings and balance. I asked them to drive it with the rear DS removed to confirm that the noise went away. I fully expected that the rear DS was the cuplrit....but it wasn't. The truck ran the same with the rear DS removed. They did say that there is a slight vibration in the rear DS and that it needed to be balanced - but not serious, and that it was not the source of the drone!

The next day we were leaving on a super road trip up to Yellowstone (1k miles each way)...so I got up early and took another good look. Well I noticed that the rock sliders had slid up on the frame and there was contact between the top of the slider's clamp plate and the foot well on the driver side and the passenger side! This meant that there was a direct connection from the frame to the body....and right under out feet...so I loosened up the u-bolt clamps slid them both down and tightened them up. Went for a drive and AHHHHHHHHH.....there was that silky smooth Lexus ride again. Its amazing what a difference it made. Our road trip was so much more pleasant....we did almost 3k miles in the end and it was awesome. Even got to do Last Dollar and Ophir passes in CO. :clap: AMAZING. One thing though....its now way too easy to drive very fast....and the mileage went from bad to worse....but I loved it.

So...in my case...my drone was because I had lost the isolation between the frame and the body. I need to find something to put between the lower slider u-bolt and the frame so they can't slide up again on the next contact with a rock. On the LX, there are only two clamp points for the sliders due to the AHC. These are OPOR sliders. They were on very tight, but our LX is very heavy with front and rear bumpers, aux tank, 6 of us etc.

Side story - that led me to check the body isolation. When we went to pick up the LX at Toyota, my wife and I went to go see a Tundra crew-max, because there's a version that can seat 6...and I hoped to go on a test drive (it was date night).... We have 4 young boys...so looking ahead to two cars that can seat us all. Anyway....somehow (good salesman I guess) we ended up test driving a Sienna. That was funny because the wife said she would never drive a mini-van....and that's partly why we bought the LX. I commented to the salesman about the road noise in the Sienna - it was more than I expected in a mini-van and more than the LX (even with my issue above)...the salesman went on to explain that it was because the Sienna was a unibody vs. the body on frame of the LX. Anyway, at some point in the night, it occurred to me that perhaps I had a body-frame contact.
:beer:
 
Joined
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2,505
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Wyoming MI
Thank you for reporting back!!

My wife didn't want a mini van either, now she can't live without it. Seriously, she will not drive anything else.
We have a Sedona and it is very quiet, so the unibody noise theory I think is BS.
 
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