Lsd and alsd question

No. That is a confusion of the terminology, which makes all these discussions more difficult. A-TRAC is MT OR / Pro only, due to the hydraulic booster.

In AT OR / Pro, you are only turning on CC and / or MTS.

Everyone else (SR / SR5 / Sport / Limited) has TRAC, due to the vacuum booster.

All models have VSC, ABS, EBD, etc.

 

[Edit, whoops @tonered already answered this...]

Only discussion below is for 3rd Gen Tacoma. Starting with the testable data that we are pretty sure of.

A-TRAC, MTS, and CC are only on the OR and Pro trims, which have the hydraulic activated brake master cylinder, which we believe has a much higher pressure and flow capability compared to the vacuum master cylinder to better allow holding wheels from spinning in 4Lo with its much higher torque (but specs have not been found yet).

A-TRAC is only installed on OR and Pro trims, manual transmission. It is a single mechanical latching type toggle switch, which if turned on will continue to be on for all future drives unless turned off. A-TRAC function is only available in 4Lo

Crawl Control (CC) and Multi-Terrain Select (MTS) are only installed on OR and Pro trims, with automatic transmission. It consists of a CC switch, a separate MTS switch, and separate a rotary dial. Both of these switches are non-latching, and default back to off on ignition power off.

I agree, people rarely discuss MTS. Our best understanding at this time is that MTS is essentially the same as A-TRAC, however with MTS, the rotary dial selects the allowable slippage between the two wheels across an axle. The 'Mud & Sand' setting allowing the maximum slippage (or wheel speed mismatch), and the 'rock' setting allowing the minimum slippage.

People have called Crawl Control just cruise control. In a way that is correct but it is definitely not the whole story. From my tests, I cannot yet absolutely say how these interact yet. If MTS is turned on before activating CC, it will stay on. MTS cannot be turned on after CC is turned on. When in CC, 4 wheel independent braking is applied (which sounds alot like MTS and A-TRAC), in addition to throttle control to try and match the target speed.

For the OR/PRO trims in automatic, the default traction control setting in 4Lo is off. If CC were just purely cruise control in 4Lo, the truck would act like it had open diffs, which it definitely does not. In 4Lo default (on OR/PRO) you get open diffs.

Now for the more opinion type stuff.
I haven't been able to prove anything definitively, but I would best say MTS is A-TRAC with selectable slippage, and CC is A-TRAC with 100% throttle control.

 

When in 4x4 and there is equal traction on all 4 tires with no loss of traction anywhere... do all 4 tires have equal power going to them? In other words, this would be the only time a 4x4 is actually a 4x4 (excluding lockers and TRAC... all open diff for the purpose of understanding).

 

It depends on what is in the transfer case. I mentioned this briefly in my discussion on what the 3rd gen tacoma has. The video is very general and covers other vehicles with different equipment. Some vehicles (most generally AWD vehicles) have 3 diffs. A center diff, a forward diff, and an aft diff. If all 3 of these diffs are 'open' then you can imagine what happens if 1 wheel has zero traction (remember torque, is constant across an open diff, so all wheels have similar minimal torque).

So on modern AWD vehicles, generally they will have some form and type of LSD, be it true mechanical type, or brake simulated type so that you still have some traction help. But that center diff allows the 4 wheel mode to be used on hard pavement. When you corner in a 4 wheel mode, the front wheel pair travels further than the rear wheel pair. There has to be a speed mismatch between the front and rear axles, or wheel slippage and binding will occur on the corners.

The tacoma does not have a system where you can use 4Hi on hard pavement while cornering. The center transfer case does not include a differential. When you engage 4Hi, you are essentially locking the transfer case causing the front and rear axles to turn at the same speed (not necessarily the same torque).

Some vehicles have a center diff that allows you to use 4Hi on hard pavement while cornering, and then lock that center diff to allow improved off-road traction. This is NOT how the Tacoma works. With the Tacoma, as soon as you engage 4Hi, front and rear axles are locked together. Note, by this I do not mean the front diff or rear diff is locked, you can still have speed mismatch front left to front right, and mismatch rear left to rear right. But the two axles going forward and aft on the truck will be turning the same speed (unless you broke it). So on the tacoma, the center transfer case operates like a locked diff. This is why you don't want to use our trucks on hard pavement in 4Hi or 4Lo while turning any significant amount. (Also why I worked on the 3rd gen 2Whl Lo mod https://www.tacomaworld.com/threads/lock-stock-and-2wheel-low-3rd-gen-diy-mod.536677/ )

Remember, open diffs: Torque same on the two outputs from the diff, speed generally may be different on the two outputs.
Locked diff (and the center transfer case in 4Hi and 4Lo on Tacoma): Speed same on the two outputs, torque generally different on the two outputs.

There I went and wrote another dissertation that is probably excessive.

 

We don't have a diff in the transfer case. It's effectively always locked when in 4x4. This is the difference between "part-time 4WD" and "all-wheel drive." AWD's have diffs in the transfer case.

Yes.

 

Thanks man for your continued help. Very informative and appreciated.

 

Thanks, I get it now! That video was showing an AWD example (when it showed one tire losing traction making the other 3 not move and then solved it by hitting the diff lock on the transfer case). Once Tacos go into 4x4 mode... it already "locks the transfer case".

 

So lets assume a 4x4 with front and rear open diffs and center diff (and no LSD or brake simulated LSD) for the moment driving straight on the road with no slippage. Note, this is NOT what the tacoma has. Engine power is delivered to center diff. Torque out to front axle and rear axle are the same because it is an open diff. Axle speeds are the same forward and aft because we are driving straight with no slippage. The same is true at the front diff and rear diff (same torque left and right, same speed no turning no slipping). Power is torque x speed (forget exact units for the moment). So except for some dynamic crap, dragging brakes, etc, in this case all 4 wheels receive the same traction and same power. Take the same vehicle and turn it, the outside tires travel further and the front tires travel further, so there is a mismatch in power between wheels, but still essentially the same torque to all 4 wheels.

Now, lets look at the Tacoma. In 4x4 with open front and rear diffs, but a center transfer case (with all traction aids off). The center transfer case generates same speed on forward and aft drive shafts, but no longer the same torque forward and aft. It is now a statically indeterminate problem forward and aft, meaning with simple statics we can't figure out the answer for the torque and power going forward and aft. We can figure out the answer only for special conditions (boundary conditions), such as you do a wheelie in 4wd. Torque and power would still be same left to right on any axle, but if you did a wheelie front axle has essentially zero torque and therefore zero power used. For the general case, you could assume that power would be same forward and aft, but you have no way to prove it easily unless you have more data.

So we are kind of at a standstill on figuring out what happens forward and aft for the general cases, but we can still learn a bit about what happens left to right with the open front and rear diff with brake simulated LSD. Open diffs have same torque out each side. Lets assume we put wheels on one side in the air. Wheels in the air have zero torque, so the computer adds some brake to that wheel when it sees it spinning. The brake applied to that wheel increases its torque required to move, which increases the torque to the wheels still on the ground as well. If it works, lets say the grounded wheel moves forward and we don't get stuck. (YEAAHHHH) Lets say this system is pretty good, and matches the two wheel speeds closely, but not 100%. The free wheel is still spinning faster than the grounded wheel slightly. Torque is constant across the open diff. Power is Torque x Speed. So the spinning tire gets more than 50% of the power being delivered to that drive shaft. This is how the front and rear drive shafts operate on the 3rd gen tacoma, (TRAC, A-TRAC, MTS all use this)

So compare that to the locked diff with a wheel in the air (and therefore no traction control required). Torque is no longer constant across the drive shaft. Speed is constant across the drive shaft. The wheel in the air has almost zero torque and a small speed. It has almost no power to it. The grounded wheel has almost the entire power being delivered to the drive shaft. (THis is how the center transfer case operates in 4hi and 4Lo, and the locked diffs of the OR/PRO when in 4Lo). Almost no power lost to a spinning wheel.


So,
open diffs mean power generally same to every wheel (if not slipping). Put brake operated LSD on those wheels, you still have essentially same power to every wheel but wheels in the air get power that doesn't move you forward. Open diffs without any LSD, wheels in the air get nearly all the power. Locked diffs (and locked transfer cases in a way) power goes to the wheels with traction and wheels without traction get almost no power.

Again, too much I assume

 

No thats good. So when you say "Locked diffs (and locked transfer cases in a way)" the non OR and PRO get the locked transfer case which isn't as good as truly locking it?

 

You engage the Transfer Case with the 4 wheel drive switch on the dash.

 

All 3rd gen 4x4 (any trim) get a transfer case whose only option is 2hi (not locked, 2wheel only) or 4wd locked. I was just trying to indicate that locked diffs and locked transfer cases provide the same type of results (uneven torque, matched speed on output shafts) .

For rugged, in general that is as good as you get. A lockable center diff in the transfer case would give more options (like AWD vehicles with 4wd on street and locking for off road) for driving on the street, but wouldn't generally be any better off road..

 

Awesome, thanks guys!

 

Will I be foolish to add a front ARD air locker? I have 2017 TRD OR 6spd manual. Has rear locker and ATRAC. I would hate to add the locker and spend the 900.00 if I have the equivalent with ATRAC.

 

I mean, this is hard to answer for someone else. There is absolutely an advantage to be had by the air locker up front vs relying on A-TRAC. What's debatable, and what you have to decide for yourself, is if that advantage is worth it. I personally lean very far towards it not being worth it. A-TRAC does a very good job providing locker like functionality. I, of course, have not put this to the test but I think it's reasonable to assume the situations where you would fail to get up/through something with A-TRAC and would successfully get up it with an air locker are very few and far between. That being said, I do think they exist.

The only justification I see for a front air locker on a Tacoma that has ATRAC is one that sees very extreme rock crawling on a regular basis.

 

That makes since. I used A-trac for the first time last weekend. And when climbing and the guy recording said that was the easiest that he has seen anyone make that up. Said the truck made it look to easy where as 2 tundras, F-250 and a F-150 Had some issues. All wheel spins and had to do a little skinny pedal. Me on the other hand had 4lo, A-trac and rear locker no wheel spin and no skinny pedal.
I think I'm going to forgo the front locker. But am going to put in New 4.88 gears.

 

How to NOT get yourself unstuck, lol.

 

I had mine out for the first time this past weekend as well. I am not really impressed with the ATRAC system. I was climbing out of a bottom on some washed out trails that had a 90 pretty much at the top. So it was a little more technical than I wanted my first trip out, but I made it through. Anyhow, it was a little longer and steeper than the other stuff. I hit it in 4 LO, 2nd gear. Towards the top when I had to turn the ATRAC kicked in and I lost a lot of momentum, having to shift to first. It wasn't real comforting, and honestly I feel like my old toyota pickups handled that same situation better. It seemed as though my engine was also limited. I may not have been using ATRAC correctly, or should've had it off to begin with but i don't like it in that situation.

 

I dont think atrac works over a certain speed. 3 or 5 mph I believe. I put 4lo, atrac and rear locker. Put in first gear and crawl up. No issues what so ever. I do have a 3rd gen 6 spd. Manual.

 

I didn't lock the rear because i knew i had a 90 to make at the top of the hill. I should've just crawled in first gear though. I was caught a couple times trying to shift between first and second. Unfortunately I ground first a couple times in low. I guess that is part of learning to wheel it. Everyone seems to like the ATRAC, but it seemed to limit me that time. I tried to cycle the traction control, but forgot it had its own switch. I guess next time I go out I will have to try it without the system on and see if i like it better. Then i will crawl with it on and see. Thanks for the input, I'm not sure if there is a difference in the 3rd gen vs. 2nd gen with the exception of 3.5 L vs. 4.0 L.

 

He may be right! But bring tow rope to pull him out.....