Front LSD and rear locking differential?

If I had to make the choice give me Atrac over lockers. Neighbor had lockers on front and rear of his dedicated plow truck. A Subaru would run circles around it on ice and packed snow. He had ice chains on all four wheels too. There are few conditions where lockers are superior and have both is the only way to go.

Without a doubt there is loss of torque at the wheel using Atrac compared to lockers. But the ability to moderate the drive on the same axle more then compensates with much better steerage and lateral stability. Throwing that much power to both sides equally is not as preferable as it seems when most off road conditions almost always have different traction conditions under each wheel. Lockers always givee that squirrelly effect which in close
Close quarters is harder to control and maintain steerage. That's why my mind set is to only use it to get moving then off it goes and it's Atrac or regular trac and high range the rest of the way.

 

Im not understanding. Other than you lose the abs and lsd part of the brakes.

 

First, there's this chart:


From this you can see that A-TRAC and AutoLSD are two separate functions.
Second, A-Trac and Rear Diff lock mode only work together below 3mph on my 2009, and I took this in my back yard, below the 3 mph.
Third, if you think about it, with the rear locked, the ABS sensors in the rear will always match, so what would ABS do back there anyway?
Fourth, the rear is an e-locker, (could also be an air locker, but that would require on-board compressed air from the factory) and truly locks, while the front is an actuator (into operation) and only 'locks' using the brakes, so I guess you could call the front an AutoLSD if that helps you keep it straight.

 

I think we have established that A-TRAC works when the normal ABS function is off. A-TRAC uses ABS, but ABS is disabled when the rear is locked, for the reasons already mentioned.

We also established A-TRAC and the rear locker can both be turned on together, but that the A-TRAC (on the front wheels only when the rear is locked) only is 'active' under 3 mph (i.e. when about to be stuck).

'AUTO LSD' is a marketing name for 2WD TRAC with engine regulation OFF (i.e. TRAC OFF MODE). The same process in 4WD (High Range) is called TRAC (2009-2011) and called TRAC OFF (2012 +).

I get the cause for confusion. AUTO LSD and TRAC OFF are the same process, but one is 2WD and the other is 4WD. The first three years (2009-2011) there was only 'TRAC' (with regulation OFF) in H4. However, they called it TRAC, even though it was different than TRAC in H2 (traction control WITH engine regulation). No quick button change in H4 (2009-2011).

Oh, but NINE drive mode selections wasn't enough!!! LOL
2012 a tenth was added, and one was changed in name, in H4: TRAC to TRAC OFF, and it now took a quick button push to get TRAC OFF to be turned on!!!

Are you guys following me on this? Do you need a drink, something stronger, maybe??? LOL

Engine regulation means the power cuts back if you try to punch it but traction is poor... to keep you from spinning the tires.

The regulation off by pushing the VSC button quickly (AUTO LSD MODE in H2, TRAC OFF MODE in H4 on 2012+) will give you full power/ no engine output regulation to get out of a stuck.

 

So what happens when A-trac is on and both front tires start to spin? Does it cut throttle? Apply brakes to both wheels and gradually release? Does it only allow power to one wheel at a time? Say this happens when climbing a steep slick sandy ledge or maybe slick wet rock. Does it go back to open diff mode then start braking wheels that are spinning?

Tyler

 

Thanks for another great write up! With so many guests and members visiting these threads, each having a different background, level of experience, and technical aptitude, re-presenting answers in various forms is a big aid to raise everyone's understanding.

 

Any traction control system will correct mismatches in wheel spin, if both front wheels are spinning at the same speed then traction control is not needed, both wheels must have the same traction. ATRAC does not regulate engine output. Traction control applies brakes to which ever wheel is spinning faster so that both wheels spin at the same speed. Power is delivered to the wheels through an open differential and wheel speed difference is corrected by the brakes, so in that sense yes it does apply one wheel at a time. If the rear axle is locked, again traction control does nothing because both of those wheels are necessarily spinning at the same speed.

edit: I forgot to mention that if your front wheels are spinning then your rears also must be spinning. And if they're all 4 spinning at the same speed then that's called regular driving as far as traction control is concerned.

The most important difference between active-TRAC (ATRAC) and regular traction control (TRAC) is how sensitive it is to wheel spin and how quickly it can respond to it.

 

I think you answered your own question. My experience has been with the A-trac active and the rear differential unlocked when climbing a steep ledge and both fronts start to spin, the A-trac continues to modulate the brakes to prevent wheel spin. Thankfully someone else posted that they could climb anything when the engine hit 3000rpm with the a-trac on, and I have found this to work on slippery ledges. It did seem a little un-natural the first time but I was pleasantly surprised. The front is always an open differential that the brakes modulate when wheel spin is measured.

 

Also mentioned earlier about those vehicles with factory front lockers. There is one thing in common with all of those.... SOLID FRONT AXLES.

There is a reason why you dont see lockers from the factory on IFS vehicles... shit breaks more easily than on a SFA, and for this reason you wont see lockers factory on the front on an IFS vehicle.

Im not saying that our tacomas cant handle a front locker (as many have put them in) but those people know when to use them and when not to.

 

I really love that I don't need to be the cheering section for A-TRAC all alone, any more! You see, it just takes time for more people to try it, who know what it was like before (with just a rear locker max.)

There is some throttle cut with A-TRAC, you can see it in the video of me climbing ONE TRI HILL with Doug and the others a few years ago in East County. However, I didn't give up and back down the slope... I put my foot down, pedal to the medal, and "woke-up" the A-TRAC, and my truck completed the steep hill climb from a stop, near the top!

Here it is!:

https://www.youtube.com/watch?v=CG3KhKR0NJk

That was A-TRAC only, no rear locker.

 

Without reading every single response on here (just skimming) A-TRAC does not compare to Rubicon front and rear lockers in the slightest. I've had both, done the same trails using both, and the Rubicon will walk over with ease what A-TRAC will struggle on (but still accomplish). A-TRAC did an impressive job for what it is and I really pushed the system hard to never use my locker, which often cost me forward momentum on hill climbs and forced the system to work 10x harder than I would have with lockers, and made me question the truck mid-climb. Throw all the fancy electronics you want at the problem, but there is zero substitution for a fully locked front and rear 4x4 on extreme trails. Front and rear lockers will win each time, every time. If you even remotely disagree then you have not tried both, or pushed your vehicle hard enough off road to see the benefit.

 

Go ahead and install a solid axle then

 

So does anyone know if the (crawl contol) function on the 16 is A-trac just with a fancy name?

 

I can agree with your post crashnburn80, but in the end, front lockers are not available on the Tacoma (from the factory) so we need to let folks know what it is so they know A-TRAC is a climbing/ crawling system that is as close to having front lockers as Toyota will have on the Tacoma, FJ Cruiser, 4Runner, Tundra, Sequoia, Lexus, etc.

 

Hello everyone

I did some work on my FJ not too long ago, so I have a little experience I can share with regards to ATRAC, Elocker, LSD, etc..


First off, the ATRAC is simply a power limitor to the spinning wheel. It doesnt 'give' you any extra traction. If you had 2 brake pedals, one for left and one for right, you could do the same thing dancing on the pedals.
Computer senses wheelspin, clamps that wheel.
Wheels are trning same speed - unclamp.

That system wouldnt work if the differential as locked as then it would apply brakes to both sides.

By nature, this system eats brake pads because they get very hot slowing a spinning wheel down even though you are crawling.

So you have to choose one or the other - ATRAC or ELock.

On the FJ, there was a simple mod that allowed you to lock the rear diff at any speed, 2 or 4.
Obviously not a good idea on asphalt.
Driving in 2wd with the diff locked was a blast. You could really get the power to the ground but the side effect was that the truck became much more 'loose'.
Back end would slide around much more BUT it was much more predictable.
You could tell way in advance you were about to start sliding. It was really no drama.
This is only adviseable on loose surfaces, as on asphalt, making a tight turn requires the wheels to turn at different speeds.

LSD is another animal altogether. It gives you the most amount of traction in the hgh speed stuff, but its not nearly as predictable.
The level of grip varies, depending on what youre doing with the throttle.
Also, it depends on the type of LSD and how you have it set up.
Some become 'open' diffs when you are not under power.
That has a huge effect on how the vehicle behaves and you have to be ready to catch it much more.

In the slow speed stuff, its not as effective as a true locker, since it will never truly lock, or if it does, its only when you are on the gas.
Some types lock more than others.

I dont know what a front LSD would do in the high speed stuff, but I suspect, it would become very understeery.
It would be interesting to try a 1.0 way set at 60% lock - for example.
That would work for the desert stuff but wouldnt do you a whole lotta good crawling.

Overall, a good locker for the front would be good, me thinks.
Locked when you need it, open when not.

Hope it helps.

(My '16 is on its way )

 

No. Crawl control is almost like off road cruise control. You set your crawl speed and the truck crawls at that speed without the need for your foot to be on the gas. This gives greater control for the throttle when doing technical stuff where it may be tricky to hold a steady slow pedal position if the truck is shifting a lot, and allows you to just concentrate on the steering. I haven't seen it in the Tacoma community, but some Jeeps would add aftermarket cable hand throttles to do the same thing for rock crawling.

Note quite.

Open diffs flow power to the wheel with least resistance. When a wheel spins, more power is directed to that wheel and less power to the non-spinning wheel (which has the traction) which is not helpful. This is especially bad if one wheel is in the air, as there is no resistance so 100% of the power goes to the airborne wheel and 0% goes to the wheel with traction, making that axle essentially useless.

What A-Trac does is apply the brakes to the spinning wheel only (which applies resistance to the diff) so that power is equally distributed to both wheels, or more power is distributed to the non-spinning wheel. By transferring power to the non slipping wheel, it gives that axle traction.

 

I know exactly how differentials work, thank you.

You are basically repeating what I said.


Atrac gives you traction by applying the brakes essentially.
It doesnt give you extra traction like an LSD or a locker which takes a 1wd open diff and turns it into a 2wd diff.

 

You are right. But I don't think 100% right.

 

the problem with something like a brake simulated LSD is say in the case of a wheel in the air and brakes being applied to the wheel in the air to transfer power to the wheel on the ground. Your torque is cut in half by nature of how a diff works. (If you stop one wheel the wheel that spins will spin twice as fast)

Either way atrac works amazing.

Crawl control simply also regulates throttle input for you so you dont have to do anything other than steer.

 

Hmmm, ok thx