Driveline Howl

Ok, here we go. I’d really appreciate it if you read the whole thing. It’s a fun one for sure.
Bought a 2006 Tacoma 2.7 5 Speed Manual with a 2.5 Coilover lift and 33s.

I have owned this truck for about 3 years and have been chasing this howl the entire time. This list is a list of things I have done to try and find the noise + upgrade the truck. Not necessarily in order that relate to the possible noise.
This noise sounds like howling in the driveline. If 10 is pedal to the floor and 1 is no throttle input. This noise happens at 1-2. For example if I coast down the mountain in Netrual at 60 mph there is virtually no noise. If I am coasting down the mountain in 5th gear and throttle off there is no noise except for about 1-2 seconds while getting off throttle.
The noise happens if I press the clutch down and take the load of the engine. There has to be no load on the engine for it make this noise. So coasting at idle it will not make the noise. It has to be slightly engaged. I will say 4WD seems to be much more pronounced and 4LO even more. At 20mph in 3rd gear in 4WD I hear it almost just as much as I do in 2WD at 60. This almost tells me the noise is related to an input /output shaft. The reasoning for it is becuase when I put in 4WD and let off the throttle a bit the noise is magnified because instead of just the rear end back feeding the end, I now I have the front and rear which makes for a more pronounced noise. I have noticed that the higher the rpms are the less of the tolerance there is for the howling noise. So for example if I stay in 4th gear instead of 5th in 2WD then it’s maybe a 40% smaller tolerance of noise then if I went to 5th. If I’m in 4LO same thing.

This noise has been going on since the truck has 30,000 miles on it.
I have had black stone labs do an oil analysis on the engine and everything came back great.
When I inspected the Transmission
everything looked pretty good as far as I could see without separating the input and output shafts and really digging in. All the bearings felt smooth and all the shift forks felt great. Also the fluids in the transmission looked great. The only thing I could think of is when I pulled the transmission off I noticed the input shaft where the pilot bearing sits had been slightly worn down and the pilot bearing did not sit firmly on it. I put a new pilot bearing on and sent it because the new pilot bearing seemed to have a little less movement than the old one. Will post pics. I also have talked to a guy with an Auto 2.7 Tacoma with the A340F trans and he seems to be having the same problem.
This noise has been isolated to either the Engine or Trans via the following troubleshooting methods.
Rear Driveshaft removed
Vehicle reached speeds up to 60 mph with only front driveshaft installed, and also only with the rear driveshaft installed.
This was to eliminate the diff has a possible option.


Napa CV axle (passenger)
Koyo Wheel Bearings
FJ Cruiser T Case Swap
Rear Diff Rebuild at Toyota Dealership
Swapped all Fluids in Diffs with Amsoil
Swapped Fluid in T Case with Redline
New Clutch
New Throwout bearing
New Pilot Bearing
R155F Trans Seperated and Inspected for wear (nothing found besides minor wear on input shaft where pilot bearing sits)
Flywheel resurfaced and torqued correctly.

Sound deaden the truck( did not help).

 

Good find, now what?

 

Now, I try and find a different transmission or see how hard it is to replace that input shaft.

 

Have you checked all of your wheel bearings, Carrier bearing, replaced ujoints, checked with stethoscope pinion bearings?

Are you sure its a howl and not a vibration?

 

I did. I posted about what I checked in the article. Also the same noise happens on the lift.

 

I am not sure that is worn. It looks to me like the step is machined, not from wear. You can see the wavy lines across th shaft from the bit chattering on the lathe when it was machined. You notice the area that is a bit yellow? That is where it is contacting the bearing. Notice the wavy marks in the yellow area, just like in the other parts of the shaft? That means virtually no wear. If it had worn material off, it wouldn’t have the wavy lines as they are less than a thou deep. I can make them go away by dragging a file across the part for a few seconds on the lathe. Clearance in the pilot area is generally pretty generous. It can move around a bit without causing issues. The fact that you can make noise sometimes with the clutch engaged, kind of points away from a pilot issue. They usually only present with the clutch disengaged.

haven’t seen aMT toyota yet. Any chance the flywheel is a two piece with isolators. The give the bmw guys problems like this.

I would suspect gear issues in mt or diff. Those gear sprockets spend most of their life loaded on just on side . Any level of engine involvement and input side drives the gears. Pup the throttle back to idle (injectors go to zero flow and zero output)or go to neutral and now the output shaft is driving the gears and using the oppsite side of the gear teeth.

Was diff work done before or after the noise. Setting up diff gears correctly is pain stacking meticulous work. If the dealer was lazy and didn’t get a good pattern on both the drive side AND the coast side, that can make noise. This is often HOURS of pulling and pressing bearings, followed by paint tests and analysis. Then rinse repeat several times with different shims. Risk of short cuts here is high, especially from folks comfortable with saying yeah, they all sound like that.

 

So as far as diff work being done. Yes it was re geared when I bought the truck. I had that issue when I bought it and I knew about it. I guess I didn’t think it was that bad but it is. I had Toyota re build the rear end as a thought for sure it had to be pinion pre load all messed up. They completely re shimmed it and everything and nothing changed. I have taken both driveshafts off independently and tested the truck and it still howls and grinds real bad. I have a video of it but I can’t seem to post video on here.

 

Unfortunately that only eliminates the driveshafts. It does not eliminate the diffs or the trans as the source, at least when the problem only appears during coasting loads. It would be different if the problem also appeared in driving loads.

start here: https://www.yukongear.com/blogs/diagnosing-noise-part-1

 

Update:

Any input shaft that does not look like this is bad. This is a brand new input shaft from Toyota. They should both be around 0.475inch or so.


As you can see on mine it has worn through quite badly.

Mine is bad and the trans is getting rebuilt with Toyota OEM parts.

This play in the R155F trans input shaft also most likely caused the main input shaft bearing to wear out prematurely causing some up and down play on the shaft support.


Now don’t jump to conclusions and assume this is your problem. I would highly advise you run through other checks like removing your driveshafts first to isolate it not being the axles.

When I drained the trans fluid it actually looked ok. Most likely cuz all that noise is coming from the end of the input shaft.

Feel free to reply and ask questions I’ll do my best to send videos your way or more photos or more on how I diagnosed it.

Really sucked that I couldn’t find any tech data on if that input shaft is bad or not until I talked to a Toyota guy that’s been doing this for 20years, but sometimes it goes that way.

So if you have this problem definelty look into it.

I don’t think the autos have this problem tho.