Type of differential...

Anyone confirm this means I have an “auto LSD” type diff?

Trying to buy some gear oil. TIA.

 

It’s an open differential. The auto LSD is just part of the ABS/traction control system, controlling wheel speed with the brakes, which puts power to the wheel with more traction. If you look in your manual under fluid specifications it will tell you exactly what you need. You don’t have to use Toyota branded stuff. You can get mobile one, redline, royal purple, choose your poison.

 

It means the computer will apply brakes to a spinning wheel to simulate a mechanical LSD.

You don't have a mechanical LSD and do not need a friction modifier in your differential oil.

 

https://www.tundras.com/threads/15-tundra-differential-fluid-change-and-drain-plug-gaskets.17221/

https://www.tundras.com/threads/diff-fluids-transfer-case-fluid-plugs.43295/

 

Yep I read those threads a couple days ago, thanks

 

front/rear open diffs. Toyota 75w85LT if in warranty. Mobil Delvac 1 75W90. Full syn, no limited slip additive. Both work great!

 

my 2016 CM has a button on the dash and a corresponding light on the dash that say AUTO LSD which lights up when I hit the button. I assume (please correct me if I am wrong) that means the LSD is on normally but goes off when I hit the button. Under what conditions would AI want to use the AUTO LSD?

 

Auto LSD is off when not illuminated on dash. It’s just traction control that will grab the brake of the slipping wheel and transfer power to the other. Ideal use of it would be pulling a boat up a launch ramp.

 

Picture how an open diff works. It sends power to the path of least resistance. So if the brakes grab the slipping wheel disc in short bursts the slipping wheel will feel like it has traction again to the open diff. So power will go back to both

 

Thank you, very informative for a non auto expert like me.

 

So the OP got the right answer here (not a "real" limited-slip differential, so no special limited-slip fluid or additive needed), but there is some common misunderstanding about how the auto LSD works.

(The confusion is created by Toyota itself - through its misleading owner's manual and dash indicator light - as part of the continuing campaign to dumb things down for the "average user," whoever that may be. It's not a big deal, but I think most people would actually prefer the straight scoop, because understanding how things actually work allows you to operate your vehicle more effecively.)

The brake-actuated, simulated limited slip rear differential ("Auto LSD") system, which selectively applies brake pressure to a slipping wheel on the side of the differential lacking traction, is actually functioning even in the default mode - regardless of whether or not you press the TRAC control button and see the "AUTO LSD" light illuminated!

The difference is that there is A SECOND automated nanny system functioning simultaneously in this normal/default mode, which restrains engine output when the Auto LSD brake kicks in. The goal is to try to automatically "correct" the steering. (For someone who's not accustomed to driving on icy roads, they will theoretically be less likely to spin out due to driver error.)

When you push the TRAC button one time and see the "AUTO LSD" light turn on, what you are actually doing is tuning off the engine power restraint nanny, so that you can power out of a stuck vehicle situation.

FWIW, the "ATRAC" system is just the addition of Auto LSD at the other axle, and it's automatically fuctional whenever you shift into 4wd. As in 2wd mode, 4hi operation requires a single push of the TRAC button to turn off the engine power restraint nanny. But unlike in 2wd mode, it is not possible to completely turn off the ATRAC (Dual-Auto-LSD) system with long holds of the TRAC button.


(Typed on my phone. Please excuse typos and grammatical errors)

 

Thank you, the best explanation I have read ....

 

Good Watch:
https://youtu.be/0-IiaNoexpM

 

So does this work differently in 4WD low? And how would, say installing an air locker in the rear, affect the auto LSD? Would the truck still try to apply brakes in 4 low with a rear locked? That would sound like a bad combination to me that could cause damage.

 

I’d say no. Once traction is sensed, ie. tire slippage is non-existent, the “auto LSD” condition is no longer present.

 

The reason I am figuring this stuff out is because I had similar questions. I've owned several vehicles with lockers or limited slip differentials, but this is the first vehicle I've owned with any nannies whatsoever - and they were driving me nuts. (The tundra I just replaced didn't even have ABS.) Additionally, my wife has a 2016 Sienna that I managed to get stuck in the snow almost every time I drove up through last winter. So, when I got this new Tundra a month or so ago and learned that it had basically the same traction system, I was determined to figure this out. I can answer SOME of your question, but keep in mind that it's new to me too.

Also, though much of this is probably similar for other years, I can only vouch for how it works on a 2018 for certain. (The truck in that video linked above does appear to have one minor difference, which I'll explain below.) So with those caveats, here are a few things that may help answer your question or put your mind at ease:

1) There seem to be many people who have added lockers or real limited slip gears to trucks with Auto-LSDs. Mechanically, there's no reason not to. Lockers seem more popular among hard-core rock crawler crowd so there are actually quite a few threads on this forum and others talking about the combination. I personally like limited-slip differentials better, but there's less info there.

My bottom-line understanding, in the case of a locker, is that if THAT system is keeping your wheel from spinning, then there's no reason the Toyota system would even try to apply brakes to it. There are sensors at each wheel (as well as everywhere else on the vehicle.) It wouldn't even kick in.

2) There is supposedly an optimum rpm range at which the Auto-LSD or A-TRAC will function. In other words, they cut out at high engine speeds and quit applying brakes. From others who swear by the system, they say this is important to figure out if you want it to be effective. It works best with a slow, controlled "crawl" while keeping an eye on your tachometer.

But to me, this also seems to imply that there wouldn't even be much overlap between the electronic, brake-based Toyota system and a redundant, real limited-slip system which tend to not even kick in until you really start digging. (I had a '70 bronco with limited slip front and rear, and I could drive through multiple feet of snow or slush by stomping on it and sending rooster tails from all four wheels. The current, factory tundra system will NOT function that way.)

3) Regarding 4WD operation in general, there appear to be some minor differences between years (or possibly between gen 2 and gen 3 vehicles?). In that video above, the vehicle stability control turned off as soon as he put it in 4HI. I can confirm on my 2018 that vehicle stability control stays on in 4HI until you manually turn it off! In 4LO, vehicle stability control is always off, no matter what year you have.

4) Conversely and to finally answer your question, A-TRAC is always on, in either 4WD mode, and there's nothing you can do to turn it off. Below is a cheat sheet I made for myself to keep in the truck until I can remember how all the nannies work, and what Toyota's endless acronyms really mean. Hopefully this will help (again this is for a 2018):

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