Differential Howl still a problem with the 4th gen. Update: Differential officially cooked

Nope, 3rd. Restating it's nothing new and it may take some of few thousand miles before they really get to experience it.

 

Not the least bit suprised

 

My 4Runner makes a howl at the front diff if I feather the throttle at 65mph. After 70mph it doesn’t howl anymore.

I tried to get several of dealers to replace the front diff but of course they couldn’t replicate it.

 

There's no break in on oem gears

 

What is the howl, why or what causes it? Does it mean something is bad?... I'm having a hard time hearing it on my gen 3 between the mud terrains, the Toyota tik , and the ambient sound of the freeway.

 

Updated OP with a video

 

Sorry, not going through globs of other howl threads, and a very quick search didn't get results...

Very off beat thought - If some leaning might be towards a harmonic issue, even on the previous gen's, does the beather mod make any difference? If it's definitely COMPLETELY inside the diff housing and a purely metal-on-metal contact thing I assume probably not. But, since a two way breather would change the air pressure inside the diff compared to a sealed breather could this be enough to upset the balance of things in there to help?

Anyone have / had the two-way and still had the howl?

... just trowin' ideas out there...
... like maybe bolt on some diff armor to see if it also helps upset the harmonic balance

 

I've had my 2way breather mod since my truck only had 923 mi. Still got the howl eventually so not a pressure issue.

 

If you took the freeway home right off the dealer lot…you’ll risk having some diff noise down the road. Sometimes the truck will have been test driven a few times before you buy…that helps. It doesn’t happen in all cases but probably a contributing factor.

In my previous life design auto shows for Toyota, we would stage ride-and-drives at the Las Vegas Motor Speedway. Our driving team would take new Toyotas and drive them lightly around the tracks to break them in. When I asked about this, I was told it was not for the engines…but to run the gears in.

In my own experience getting rear gears replaced in other vehicles, I battled noisy diffs until I learned to take it easy for the first 200 miles. Never had a single issue since…new or rebuilt.

I bought my 2023 Tacoma 200 miles away and I did several 20 minute in-town drives with one hour cool-downs before driving 50mph all the way home. Rear diff is quiet as a mouse.

BTW, I took a pyrometer with me just for kicks and that diff got very hot (approaching 280 deg) within the first 100 miles.

 

Not my first new vehicle brake in by far. I drove home starting with 4 miles on the clock. I varied the speed on back roads and even broke in the brakes properly. The diff got louder immediately and peaked at 2500 miles. It takes feathering at 55mph to get the noise now, but it’s there.

The fluid is at level and clean. I have experienced many brake ins with similar drivetrains in commercial applications where the vehicles are beat on from day one without issue. Smells like poor machining and design period. It’s not the end of the world, just annoying AF.

 

just slap some KO2s on it and the tread noise will drown it out

 

Asking for a friend, if your singing is drowning out the diff howl?

 

If the Taco heard me signing, it would start howling...

 

Updated OP

 

Any pics of the "burnt oil full of metal"?

 

no just going of what the dealer told me. I doubt I’ll ever see it.

 

My 2011, i spent 4 years with the dealership trying to get the howl sorted. first they found the transfer case was failing (WTF?) then the rear wheel bearing (ok free bearings are great). they eventually replaced the rear diff for me, and boy, life was sweet. Quiet, problems finally gone. A month later the truck was totalled...

 

Maybe it's just the video, but I don't hear anything concerning with noise cancelling earbuds on.

This same old song and dance happened many times in the 3rd gen world. Folks hear the "howl," make a trip or two to the dealer, dealer finally says they found bad oil, or metal in the oil, or whatever else and so they install a new diff. After new diff the problem is exactly the same because it turns out that there was never anything wrong with the first diff. Highly doubt the oil is burned and metal, especially on the magnet, is completely normal. But without getting to see any of that since it's the dealer service department, I'd just let them do whatever they say they'll do and then carry on. If it makes noise afterwards, quit bothering with it.

 

videos never do these type of things justice but trust me it was annoying AF listening to that every time you’re on the highway. I had 2 separate people call out the noise while they were riding in the car.

The differential howl on the Tacoma has been a topic for the past 20 years. If every single Tacoma had the howl then ok you could maybe pass it off as characteristic. Even if it is a “harmonic resonance” issue, Toyota has had plenty of time to redesign. A lot of Tacomas have the howl and many don’t so obviously there is a design or manufacturing problem somewhere that causes the discrepancy.

In my case my 500 mile oil is burnt due to excessive temperature which can only happen from excessive friction. I’ve only heard of one other case on the 4th gen with the same symptoms and fix as mine so hopefully the howling diff problem is a thing of the past.

 

OEM gears are no different than aftermarket, they are still NEW . Not some magical toyota metal. They set the preload and backlash and that all.

https://www.motortrend.com/how-to/129-1207-new-gear-set-break-in-or-break-down/

https://www.yukongear.com/help/faq/...he-break-in-proceedure-for-a-new-set-of-gears

https://eastcoastgearsupply.com/ft-1479-new-gear-break-in-procedure.html

https://nitro-gear.com/break-in

This picture is from a break in change on a new corvette. Didn't take one on my first change. Didn't look quite as metallic but there was definitely a shiny silver sheen to the gear oil. If for the sake of $20-$40 in gear oil you want this stuff eating away at bearings and seals its your DIFF. Is it going to explode at 501 miles no. But over the long run this isn't going to do it any good.