VSC Off, ATRAC On Mod complete!

[CJ3Flyr]

I completed the VSC-off mod on my T4R. The cool thing about this mod is the ATRAC is still active.

A great thank-you to Andries at T120. This is his hard work not mine.

In 2wd dash lights are on (VSC & Diff lock). I didn't mess around enough to decide if VSC is working, traction control IS working; I'm assuming it has full VSC. It has all the familiar noises and accompanying reduction in power. The system seems to get confused if you attempt to change from 2HI to 4HI with the switch on. Lights get stuck in flash mode.

In 4HI it works as advertised You have an [i][u]unlocked Torsen center diff and no interference from the VSC; the VSC and Diff Lock light are on. You can definitely feel/hear ATRAC doing it's thing. The same deal in 4LO... I can lock and unlock the diff while in 4HI (or 4LO) with my switch on. It locks & unlocks ok. When unlocked the diff lock light continues to flash even after the diff unlocks. It is not a perfect mod. It beats the heck out what Toyota gave from the factory. I am thrilled!

My advice is to not do a mode change with the added VSC switch on (grounding the wire). I may retract/amend that as I learn more. For now I plan to lock and unlock the diff, switch 4HI to 4LO with my added VSC switch in the off (ungrounded or open) position.

The bottom line is it's a great mod that facilitates the use of 4HI and 4LO without VSC interference and the center diff unlocked.

Andries saved me thousands! I was having serious 'VSC-off' envy of the 2008 guys!

This is the original Andries, aka Bulldog, thread: http://www.toyota120.com/forum/showthread.php?t=3817 Below are some ‘how-to’ pics.









Take care to make sure the wire doesn't contact the very warm heater core coolant piping.

[CJ3Flyr]

You can't see it but I put a couple of connectors on the switch wires also so that I can take it apart later without pulling and/or cutting wires.

[mastacox]

What's the advantage of being able to use ATRAC with the center diff unlocked? I think I get the VSC part, but why does it matter if the center diff is locked?

[Good Times]

I think he meant to say turn off VSC and keep the center diff unlocked. Right now if you turn off VSC, it locks the center. This mod just gives you the ability to disable the VSC and still have the ability to either lock or unlock the center.

I'm not sure what the inherent benefits are having a disabled vsc and an unlocked center is. I would think I would want it locked so I get the 50/50 transfer of power. Your guess is good as mine. One on the dirt, I usually lock the center right away and call it a day

[CJ3Flyr]

Brian and Lance, point well taken... Why? I like to be able to do tight turning on hard packed trails with the diff unlocked. Truth is it'd be just fine with the diff locked but it's my preference. Recently on some wet GA clay I was actually able to steer better (less front end plowing) with the diff unlocked and still able to rely on uninterrupted engine output.

I have some more work to do. When done the goal is to have the equivalent of the 2008's (4wd) VSC off switch.

[Good Times]

Chris,

I'm trying to better understand this because it appears you're trying to favor the torsen limited slip differential in the center. Basically playing with the 30/70, 70/30 power distribution utilized by the torsen limited slip differential.

variable 30/70 to 70/30 power distribution VSC off (custom configuration via mod)
50/50 VSC off (factory configuration when center diff is locked)

When the atrac recognizes slippage in the rear axle, power is redistributed via the LSD in the center diff to 70/30 (front/rear) instead of the 30/70 (front/rear default). The same applies if slippage is found in the front (basically vise versa). The slippage is found by the ATRAC system which is getting its information from the ABS sensors since ATRAC is never turned off.

The only concern I see is that if the rear axle instantly gets slippage you'll suddenly have a significant shift in torque to the front which can cause oversteer if you are turning. Or do I have this mixed up. I would think that having a fixed 50/50 power distribution would be better than a variable power distribution system. I'm not sure, all this thinking is confusing me. Maybe you'll have a better explanation.

[CJ3Flyr]

When the atrac recognizes slippage in the rear axle, power is redistributed via the LSD in the center diff to 70/30 (front/rear) instead of the 30/70 (front/rear default). The same applies if slippage is found in the front (basically vise versa). The slippage is found by the ATRAC system which is getting its information from the ABS sensors since ATRAC is never turned off.

The only concern I see is that if the rear axle instantly gets slippage you'll suddenly have a significant shift in torque to the front which can cause oversteer if you are turning. Or do I have this mixed up. I would think that having a fixed 50/50 power distribution would be better than a variable power distribution system. I'm not sure, all this thinking is confusing me. Maybe you'll have a better explanation.

Great discussion... 1st, The best handling off-road vehicles are probably the rally cars such as the Audi's, Subaru's and the Mitsi's. They use some type of differential in the middle. Variable front to rear biasing seems to be a requirement for the best 'dirt road' handling and it 'feels' that way to my untrained driving skillset. 2nd, it is my understanding (I may need some schooling here) that ATRAC and it's programming, when the VSC is off, looks at the front & rear axles separately. It certainly feels that way when I encounter slippage. Does that make sense?

Overall it just feels better...

When I try a 4wheel donut/powerslide on wet grass it's much more fun with the center diff open as it bias's the rear more power

[Good Times]

Ok I should correct my previous comments cuz it's wrong. I posted this without thing this through so here's my revised comments:

The torsen limited slip does not interact with the ATRAC (it can't duh cuz it's not an electronic unit). The LSD just checks for slippage at the output driveshaft (front/rear) and will distribute between 30/70->50/50->70/30 depending on output slippage. This system is the Tosen Type 3 (latest version to date I believe) which has the capabilities to have a biased power distribution to mimic a more rwd style power distribution).

The ATRAC on the other hand just checks for wheel slippage at each corner and will use the brakes to apply/redistribute power to each corner. ATRAC has nothing to do with VSC as the VSC controls the throttle I believe (right?).

So basically answering my own questions, I can see how having the VSC off and everything else working would be good. It's basically similar to that of an Audi quattro; Audi utilizes the same Torsen Type 3 diff so in theory the driving characteristics would be identical.

(Some background info: Torsen Type 2 was a default 50/50 power distributing LSD. so the Type 3 is just an advanced diff that mimics a rwd driving characteristic vehicle with the benefit of the awd/4wd setup.)

Here's an example so we can review the different style conditions:

Parameters:
Condition - wet surface
Terrain - hard packed (say asphalt)
Road - hard 90 degree turn

Example 1: (VSC OFF only mod)
based on these parameters, before you enter the turn you'd be 30/70 ratio. once you enter your rear would encounter torque slip (rear slipping I believe) so the power would get immediately redistributed to 70/30 instead. since more power is now distributed to the front you'd be able to drive more like a fwd car and continue thru the turn and exit smoothly.

Example 2: (factory default - center locked vsc off)
50/50 ratio throughout the entire scenario.

So thinking about these two different styles of driving I guess it just depends on the drivers skill level or comfort level in terms of how they want power to be distributed. It's like saying asking for a fwd vs rwd vehicle for rally racing or something equivalent.

So the bottom line is if users want to experience the variable 70/30,50/50,30/70 center diff controlled environment then this mod would be great. those that just want 50/50 power distribution doesn't need this mod.

At any rate just another cool mod.

[CJ3Flyr]

I finally got the Holy Grail of this mod...

As you may know this mod allows for VSC off, center diff unlocked operations while in 4wd. What was missing is the ability to run 2wd VSC off. I got it



To use 2wd VSC off is strictly a procedural variation of the existing mod.
[I]The following in conjunction with the mod gets you 2wd w/ATRAC and no VSC:

- Select 4hi and allow it to engage.
- Select VSC off via the installed switch
- Select 2wd. Feel for the telltale 'normal' light thump as it reverts to 2wd. You are now in 2wd w/no VSC and fully functional ATRAC.

NOTE:- Both 4wd indicator lights will flash, the VSC off light will be steady. I drove like this and did the cycle many times with no ill effects. I did two, full 360+ donuts too

- Before shutdown or reselecting 4wd shut the VSC off switch to off (ungrounded position).


EDIT: I will also add there's no audible evidence that in it's "state of confusion" it attemping to do any mode changes. If you listen carefully you can hear relays clicking under the glovebox when the 4WD is attempting to change modes. When driving in 2wd or 4wd with the added VSC off switch in use I hear no clicking.

Enjoy!

[AlexJet]

This is a nice mod and many guys done it. So far I didn't hear that anyone gets any drawbacks.
I think I've read on some forums that there were guys engaging the switch in 2WD mode and it worked on V6 models, but there were some complications with turning it off....