50 seems early no matter how "severe" unless you're in 4x4 off road for half those miles. ESPECIALLY if there are ZERO shifting issues or any cooked fluid smells.

That being said, i have a fear of touching the transmission fluid for the OP's very reason lol. So i may be biased.

I think it would be really interesting to be able to do either long term testing or have some way to collect enough data to see if transmissions that get serviced last longer than ones that don't. Based on the small sample set on this forum, my bet would be that your odds are better by doing nothing other than possibly adding a cooler than by having the trans fluid changed. It seems that almost every transmission failure that I've read about on this forum is the result of a fluid change and there are very few or no transmission failures I've read about that were due to not changing the fluids or for any other reason in transmissions that had not been serviced. Based on very little data, I'd probably say that fluid changes done right really is the best choice, but unless you're doing it yourself and know exactly what you're doing, it's better to leave the OEM fluid in for life. And that there's a high probability that 300k miles or more is pretty consistently do-able without ever changing the fluid. So unless you're towing heavy regularly or working it really hard, I'd favor not changing the fluid ever.

Now for my hypocrisy...lol. I have a couple cases of WS fluid in my shop and was planning to change my 4Runner trans fluid at 75k before I sold it. I used it pretty hard and thought it was probably a good idea to exchange the fluid. I'll probably use the fluid to swap out my Tundra trans. Mostly because I have the fluid and the use history is unknown. Based on the condition of the truck and the fact that the inside of the hitch and hitch pin hole have almost no visible signs of wear or chipped paint, I'd bet a that the truck never once had a hitch put in or towed anything. I'll change that. Haha. First trip I'll take will be towing a travel trailer to Alaska in June. So it'll get a little workout. I've been watching the classifieds for a used space shuttle to tow, but the market right now is pretty tight.

I've been kicking around some ideas on how to make an idiot proof transmission fluid exchanger that would swap the exact amount of fluid back in as comes out. It would seem like that should make the exchange very reliable and avoid a lot of the under-fill issues we see. But I haven't come up with a way to do it inexpensively with easy to find off the shelf parts. The biggest issues I am struggling to find the solution to are how to make it automatic without electronics. The obvious solution I see is to use a vessel with a barrier so that the fluid pumped out displaces the same volume of fluid back into the transmission. The problem is that it needs to be a low friction diaphragm. So a floating piston type design won't work. And a bellows type separator is expensive. Not sure what else there is out there that would work well. I don't think air pressure between two sealed vessels is a good solution. And the second problem is temperature. The volume expands when warm so if you remove warm fluid and exchange for cold fluid, you'll likely end up with too much fluid or the reverse. So you'd need the new fluid to be at the same temp as the old fluid. And mineral based oils expand at different rates than synthetic oils. But the basic info suggests something like 10% expansion between 32* and 200*F. If the fluid going in is room temp and the fluid coming out is operating temp, you'd overfill by 8-10% using the same volume. That's over a quart too much. I'm guessing that's why the fluid exchange machines fail to get a proper fill.

So maybe it's just not practical to do a perfect swap without the final fluid check. IMO it would be pretty useful for Toyota/Aisin to re-design the trans fill system and oil pan so there's a wider range of acceptable fluid volume and ideally make it so that it can be checked when hot or cold. Maybe that means two check plugs in the pan and you use one or the other depending on trans temp. Having the trans pan just a bit larger so it could be plus or minus 1 quart would go a long way toward avoiding most of these issue I think.

I hope in this case the dealer figures out what went wrong and fixes it. The dealer should be following the FSM procedure to do the trans fluid exchange. I'm not sure why they'd do anything else. If you have a vehicle lift, the FSM procedure handy and all the tools, it's really pretty straight forward. And that's what you expect at a dealership - you pay more for them to do it by the book as intended by the engineers who designed it. Unfortunately that's not always what you get.

Your conclusions are based more on emotion than real actual data. The reason you don’t hear about failures with non-serviced transmissions is that that the owners sold them before that occurred. You yourself did the same with wishful thinking evidenced by bottles of WS still on the shelf.

You are over thinking on the fluid swap measurement device, which is completely unnecessary. The final measurement is done with the fluid temp at a range 104 to 115. The amount of fluid expansion is immaterial. Just get it to temp by idling 20 minutes and starting your fluid change approximately 2 quarts at time until clear or you’ve replace the entire amount (based on empty fluid bottles). When done, pull the fluid level drain and top up if necessary, or let drain if too full.

We have 300K on 2014 SR 5 transmission. I’ve done fluid changes every 120K miles on the transmission using Valvoline Synthetic ATF. If you believe some here, I’ve done everything wrong, yet the scoreboard says otherwise.

Knowledge spawns confidence. Ignorance spawns fear.

The temperature range is relatively wide as long as you're starting from a cool drivetrain. You can even skip needing the scantool or jumping pins (though jumping pins puts it into a "let's warm up faster" logic) and use a decent quality IR Thermometer to measure the pan (make sure the pan is relatively clean, doesn't need to be spotless, just not caked in dirt or mud) because the temperature sensors are in the valve body, so if you shoot for roughly the middle of the spec you should be fine. The fluid itself doesn't expand, but I have noticed that once it starts getting into the temp range you may notice the fluid volume coming out may increase a little, my guess is some sort of thermal bypass or something. It doesn't have to be super precise, the tolerances for the temperature and the slightly vague "watch for dribble" to measure give you some leeway.

It is also totally fine to overfill it a quart or so while you're doing the flush, as long as you drain/adjust it before driving a significant amount. I will often overfill the transmission by a a half to a quart and pull the check plug within 5° of spec to adjust, it's a bit easier than trying to quickly top off when you're at the edge of spec.

Also, make sure the A/C is off and that you're not loading up the vehicle so the idle stays stable
Idle fluctuations will mess up the reading. It's a bit convoluted, but not rocket science.

People saying 50k is too early...I am of the mindset that an ounce of prevention is better than a pound of cure. Old, burnt, dirty fluid is the enemy of transmissions. I would definitely change my fluid often (either myself or a competent shop). I know it's a different animal, but my C63 needed the trans fluid changed every 40k per the manual and it was always black and burnt. I kept up with the maintenance for 100k, sold the car, and then within 500 miles the trans gave out. Now I don't know if it was abused after sale or not (I suspect), but I wish I had done the trans fluid more often to keep fresh, clean fluid in there. I think 50k seems more than reasonable.

I also agree that if the diff wasn't making noise before, it likely isn't the source of the sound. I'm betting on the fluid level being low

I'll update this post when I find the official definition. But of my head, things like:

-Stop and Go Traffic
-Trips shorter than 10-15mi
-Frequent Idling
-Dusty/Smoggy air
-Extreme changes in temperature (i.e. summers are 90-100°F, winters are freezing or below with snow)
-Regular driving with a loaded vehicle/towing (lifted w/ tires will fall under this category as it affects the drivetrain)

Are all conditions that usually fall under that "Severe Conditions" header.

I don't think we know. Not emotions. Just lack of data. Unless you have some actual data? I'd love to see it if it exists. Almost universally the transmission problems we see on here are the result of fluid changes gone wrong. Just a probably comparison. I think it might favor not changing the fluid ever in most cases.

Your transmission might have been just as reliable with no oil changes. My last one had no issues out to 200k when I did its first change just because it seemed like maybe I should. Probably didn't need it. There's a ton of 200k plus a750f transmissions out there that have never had a change. Many of which have v8s hooked to them. It's not a GM automatic. We don't see many internal bearing failures or planetary gear catastrophic failures liked I've had at low miles on my GM stuff despite 15k mile oil changes. The aisins seem last a long time no matter what you do to them in most cases. As long as you don't run em out of oil or over fill too badly.

I will say that the A750, A760, and AB60 have been fairly solid transmissions from Toyota. I've probably replaced more AB60's than I have A750's, but it's more people being idiots and trying to use their Tundra/Sequioa like a 3/4Ton diesel truck or not servicing their transmissions regularly when using their vehicle for towing their 5th wheel.

The A750 in particular held up pretty damn well, the ones I did end up replacing were usually in the 150-200k range and probably hadn't seen as much maintenance as they should have. I would say that the 1GR-FE/A750x and 2UZ-FE/A750x was one of Toyota's most solid and fairly bulletproof drivetrains.

I've seen more U660x and U760x fail closer to the 100-150k range. Maybe it's because they didn't get serviced early when they should have or maybe people shouldn't be trying to use their Rav4, Venza, Sienna, or Highlanders as RVs and/or towing their 20ft boat? Not entirely sure, I think also they may be more susceptible to burning through that WS ATF when dealing with a lot of stop and go traffic and short trips?

But for the most part, Toyotas transmissions are usually pretty robust and we don't replace as many as you would think, despite some customer's best efforts to not maintain their vehicles.

I do transmission fluid changes at 25K. Never flush.

Here's an update:

Service Manager says they reserviced the Trans. Fluid is correct. They hooked up chassis ears and noticed a noise coming from rear diff. Found metal in the fluid. Removed Diff assy and found more metal. Rear Diff is on backorder until June 8. Family Vaca starts tomorrow for 12 days so don't really need the truck. They reinstalled the original diff and told me I can drive it home to wait on new Diff. I personally think that crazy if the thing is bad like they say. Worry that further damage could be done to the axels.

Keep in mind I never experienced any noise or vibration from the Diff. NO metal when I changed the fluid @ 30k. Who knows... I don't know what to believe at this point. everything is being covered under warranty.

I did find some hits when I searched for Diff problems. Seems 2018 to 2019. Most occurred with the 1st 10k

Your first sentence is most accurate: we don’t know or have the data. What you see here are the exceptions. Turns out the OP on this thread did not have transmission problem, rather it was a rear diff.

What I do know on the trans is the more and heavier you tow, the more heat you generate, the more you shorten the life of the transmission. All it takes is a one or two overheats towing a trailer up a grade and it’s done. At most I have used my wife’s 4Runner to tow my drift boat which weighs 450 lbs, plus the single axle trailer. All total, probably no more than 800 lbs. if I want to tow big, I use my 3/4 ton diesel Suburban.

Moving up to an HD truck is a good idea for towing. The 4Runner chassis does really well. The power band of the engine isn't great though. It just requires too much RPMs for decent towing comfort. Not sure it's that far off from the 6.5 diesel though TBH. I haven't driven a 6.5 in probably 20 years. But the 4r has much bigger brakes and nearly 100hp more than a 6.5 diesel suburban. I bet if they were both rated on the SAE tow capacity the 4Runner would probably rate higher given the lower gearing and brakes. But it's still probably more comfortable towing with that heavier chassis and longer wheelbase.

We had a 2001 HD 2500 with the 8.1 and Allison. It was great for towing. As long as you were okay with 6-8 mi per gallon. And didn't mind buying a transfer case every 50k and a transmission every 100k. Was a fantastic highway cruiser. But it just didn't hold up to daily towing duty for our landscaping company and plowing snow in the winter. On the plus side - when the transmission went out, you knew it was out. Spin on filter was full of chunks of the planetary gear set.

My 6.5 has a much larger turbo for towing, upgraded high flow water pump, upgraded exhaust from turbo back and a tune flashed on the ECM. It is producing around 270 hp and 485 ft/lbs torque vs the stock 195/385. You definitely feel it. Aside from torque and hp, it’s the drivetrain (trans), rear axle gear ratio, suspensions and brakes that determine how much you can tow.

Front brakes have been upgraded to the dual piston calipers of the next era GMT-800 trucks. The pads are much bigger and the stopping power is substantially better. Some guy made a YouTube video on this conversion, largely from reading my thread on another forum.

Truck was rated to tow 8,300 lbs, but easily handles 12,000 lbs.

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Went into the dealer today and picked up my rig. Leaving it at the house while waiting for the chunk to arrive hopefully June 8. The service provider was again mentioning that I failed to put a conditioner in with the Gear oil when I changed the the fluid. I told him to please show me in the manual where it says to add a conditioner to the diffs. And show me what the conditioner looks like in a bottle.
Again I told him I put in Toyota GL5 75/85w.

Swooshing noise still present with mild accelerations. I crawled underneath once I got home to inspect things. They didn't even wipe down the Diff after servicing it. Oil all over it. I also noticed my skid bolts were not tightened all the way from the trans service. The front of the skid was all dirty with grease and dirt from laying on the ground.

Just sad how no-one has any pride in doing a good job anymore. I know that sounds picky but how hard is it to wipe something down.

I'm pretty sure they drained that Diff during the Trans service and forgot to add oil back into it. They asked me about an hour after they had been working on the trans if I wanted the diffs serviced. I told them no they had already been done. Maybe all of this is just a giant coninsidence but I am 100% certain that sound was not present when I brought it in. Sorry for the rant... Thankfully its all being covered under warranty.

That sucks if they forgot to fill and you ran without oil for a while. Not much you can do to prove it later. And it definitely happens. A shop I worked at many years ago had a few of those, including an engine the tech forgot to put oil back in. That one resulted in a new engine for the customer.

The diffs don't have any friction plates in them, so there's certainly no friction modifiers needed. If they added something to make it quiet - I'd expect the diff to fail relatively soon. I'd actually change it myself again if I were you to put the right fluid in and make sure they didn't put 75-140 or something like that in to hide it.