Originally Posted by DoorDing
I'm certain VSC and ATRAC do have some effect on each other; they have to, since they utilize the same systems to accomplish their task. My guess is that VSC can override ATRAC output, since the overall stability of the vehicle should be more important than any single wheel's available traction. The main difference is that ATRAC doesn't use yaw data, while VSC obviously does.
I understand why Shemp prefers dumping ATRAC/TRAC naming for LSD. My issue with that is that is all the e-diff solutions are a bastardization of what a true, mechanical LSD really is, even if the end result is similar (at least until the brakes overheat). Toyota would do well to pick one name and stick with it. Since they offer a mechanical LSD in some models, I believe it'd be best to reserve any use of LSD for that differential, and only use TRAC for open differentials that are being controlled via brake modulation. A-LSD is the worst of both worlds, since it's not an LSD, and it's a needless duplication of TRAC on an open differential.
I don't agree that ALSD is any kind of "bastardization". The system has more strengths over mechanical LSD than it has weaknesses.
It also doesn't help for clarity to limit the use of the term "LSD". There is no model of Tacoma offered with an old fashioned mechanical LSD unit any more. They were only available up to 2008 MY.
In fact, ALSD and LSD are a lot more similar than you would initially imagine. The mechanical differential used a series of friction disks (brakes) to control the motion of the two wheels relative to each other. If one started moving significantly faster than the other, the disks would engage to some degree and slow down the faster moving wheel relative to the slower moving wheel.
With ALSD, it uses the main brakes to slow down the faster moving wheel relative to the axle housing.
On a superficial level, ALSD might seem to be less efficient than a purely mechanical LSD. It might leave the impression that energy is taken away by the brakes. That, however, isn't really the case. Imagine that you're stuck with one wheel spinning and the other stationary. 100% of the energy produced by the engine is being lost in the friction between that moving wheel and the ground, yet you aren't moving. If you fully lock that spinning wheel, then 100% of that energy is directed to the opposite wheel. If you 50% lock it, 50% of the energy is directed to the opposite wheel, and 50% is lost as friction to the ground. Yes, of course a slipping brake is going to absorb some energy as heat, but the same thing is happening in a purely mechanical LSD.
So a more thorough analysis suggests that ALSD is no less efficient than a purely mechanical LSD on an energy utilization basis.
Next up is efficiency of activation. A mechanical LSD requires a certain minimum amount of slip in order to lock the plates together. ALSD also requires a certain minimum amount of slip in order to know to activate the brakes. Meaning, of course, that BOTH need to actually slip in order to respond. I don't see any advantage for either in this respect.
Up to here, everything between LSD and ALSD seems to be about equal. There are, however, some noteworthy differences;
First up is cooling. Suggestion of ALSD overheating and ceasing to react. As far as I can tell, this is predominantly affecting models with the electro-hydraulic brake boosters (ATRAC -- TRD offroad). It is the brake booster itself that overheats, rather than the brakes (which don't have temperature sensors). The models with vacuum boosters have a similar glitch, but not quite the same; loss of vacuum. The vacuum booster can only run the brakes so much before running out of vacuum.
Now obviously, a mechanical LSD won't suffer those downsides.
The big downside to a mechanical LSD is what happens when you wear out the disks. It is a bit more involved of a repair to replace worn out LSD disks than brake shoes.
ALSD has additional advantages over mechanical LSD: that it can be controlled electronically, so can relate front to rear wheel speed, and can be activated in circumstances like yaw sensor.
The biggest advantage that ALSD has over mechanical LSD is that it can operate on the FRONT in 4wd.
And last, of course, ALSD can be deactivated. Mechanical LSD cannot.