Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

[1983FJ60]

tjpyles previously said:

I know that the manual says to reduce speed to 50mph to shift from 2H to 4H (in automatics), but if you are driving in wet or snowy conditions on a highway is there limit to "safe" speed in 4H mode. Obviously, the conditions of the road stipulate to a great extent what is a safe speed, but what is safe for the 4H operation of the engine. The other night when driving home, we ran into a heavy downpour with puddling on the highway, and I was concerned about how fast I should/could go with 4H active?

You should NEVER drive in 4H above the max speed.

Hell, I wouldn't go over 40.

That system isn't designed to be operated at such speeds off or on-road--regardless of the conditions.

[booboo]

Thanks for the great writeup.

At the dealership I knew something was up when I was being sold ATRAC as THE traction control system on the manual implying without UR the FJC had NO traction control system. I was thinking "if it is a full time four wheel drive and doesn't have any means of detecting wheel slippage (mechanical or electronic) to direct power from slip wheels to grip wheels what's the point of a full time 4wd system?" I knew something was afoot.

Now the question I have left is...

Is there a way to turn off any and all systems that would use breaks to transfer power? ...allowing wheel slippage and unadulterated winter fun? From your writeup it appears there is no way.

In my current car, a Volvo v70R (300hp, AWD) I run Dunlop Winter Sport M3 for snow tires and can turn off "Dynamic Stability and Traction Control" by pushing the DSTC button five times. I can get a nice roostertail of snow and slide the backend out around a snowy corner. With the system on the brakes kick in and the engine revs down before the fun starts.

[edit: I searched and found my answer. ]

Thanks,

--booboo

[Landrover]

I just wish you didn't have to be in 4L to operate the diff lock. Sometimes I just want to be in 2WD and do doughnuts

[JLam]

tjpyles previously said:

I know that the manual says to reduce speed to 50mph to shift from 2H to 4H (in automatics), but if you are driving in wet or snowy conditions on a highway is there limit to "safe" speed in 4H mode. Obviously, the conditions of the road stipulate to a great extent what is a safe speed, but what is safe for the 4H operation of the engine. The other night when driving home, we ran into a heavy downpour with puddling on the highway, and I was concerned about how fast I should/could go with 4H active?

I don't know that you really need to be in 4H just for wet roads. Think about all those 2wd cars driving around just fine in the rain. Snow is a different story, but if it's only rain, IMO, I'd keep it in 2H.

[cruiserlarry]

tjpyles previously said:

I know that the manual says to reduce speed to 50mph to shift from 2H to 4H (in automatics), but if you are driving in wet or snowy conditions on a highway is there limit to "safe" speed in 4H mode. Obviously, the conditions of the road stipulate to a great extent what is a safe speed, but what is safe for the 4H operation of the engine. The other night when driving home, we ran into a heavy downpour with puddling on the highway, and I was concerned about how fast I should/could go with 4H active?

How fast would you like to go in snowy / wet road conditions ?? I'd venture to guess the 4H transfer case will put up with higher speeds (it does in my other vehicles), but really, I'd recommend caution with your speed if your concerned enough to use 4h to make it through...JMO..

[cruiserlarry]

Landrover previously said:

I just wish you didn't have to be in 4L to operate the diff lock. Sometimes I just want to be in 2WD and do doughnuts

Alocking diff will prevent doughnuts, not assist them - you need an open differential to get one wheel to overpower the other for a doughnut, unless you're on wet / icy pavement...

[Tranman]

Landrover previously said:

I just wish you didn't have to be in 4L to operate the diff lock. Sometimes I just want to be in 2WD and do doughnuts

FYI, Percy previously posted a link to a TTORA that gives instructions on how to hack this so that you can use the rear diff lock while in 2 wheel. He also said he was waiting for his warranty to run out before doing this himself.

OK found it....

Percy previously said:

Tranman - The mod for the rear locker has been figured out. You can do a search on TTORA and there is actually a very good write up. It is similar to the grey wire mod on older toyota 4x4's, but requires the installation of a DPDT 20 amp relay. This will allow you to lock the rear no matter what transfer setting you are at. I plan to do this to my 06 Taco, but not until it's out of warranty.

[Dragon]

JLam previously said:

I don't know that you really need to be in 4H just for wet roads. Think about all those 2wd cars driving around just fine in the rain. Snow is a different story, but if it's only rain, IMO, I'd keep it in 2H.

Agreed. In rain you want your VSC working for better vehicle control. The VSC is turned off when you go into 4WD.
It's all about control of the vehicle.
ATRAC is similar to TRAC. ATRAC available in 4WD and TRAC in 2WD, but sometimes in 4WD you want the ability to turn it off (like sand when you want the tire spin), so there is a button to do so. There is not a button to turn off TRAC while in 2wd as you always want that assistance while you are driving to the mall on a rainy day.

At the risk of repeating myself, all of this was designed for vehicle control, not for donuts and not for drifting.

[Kansas Law Dog]

The big distinction between TRAC and ATRAC is that ATRAC is a traction assist while allowing full engine power to be provided.

TRAC works when it senses slippage (such as on snow) to apply pulse braking to the slipping (spinning) wheel and cut engine power for driving control. Because TRAC works in both high and low ranges, when higher speeds are probable, cutting engine power is a safety feature.

The reason ATRAC is limited to 4WD Low Range is because it is an aggressive traction control. When negotiating a rough section of trail where a wheel losses traction, through suspension articulation (one wheel lightly touching the ground) or wet slippage, you don't want the engine to cut power to correct the consequences of traction loss. You just want the slipping wheel to stop spinning. The engine torque is required and cutting power would defeat the effort to overcome the obstacle.

[Thai]

What KLD said...ATRAC is a more aggressive form of TRAC. ATRAC does not cut engine power and it will brake the spinning/slipping wheel quicker and more aggressively...it is for off-roading only or for slow speed traction.

For example, TRAC slows down the spinning/slipping wheels. This is good in all-weather driving in which you do not want ABS brakes to stop a wheel completely...this may create instability on-road. ATRAC, on the other hand, is for off-roading only. Thus, it can actually stop the spinning wheel altogether for a short period of time (aka brake the spinning wheel to zero mph). This allows for more efficient transfer of torque to the other wheel with traction.

Here is a thread i wrote a long time ago about ATRAC and torque transfers: http://www.toyota-4runner.org/showth...&threadid=5036

VSC is for stability to prevent oversteer and understeer. In theory, it has very little to do with straight line traction (this is where TRAC comes in). VSC is to save your ass if your car loses control on an off-ramp for example.

Auto LSD is another BS term Toyota uses to describe traction control. Marketing term.

Although (A)TRAC and LSD are two different thing, they FUNCTION (in practical terms) similarly...aka, they help your FJC move forward over poor traction surfaces. Therefore, auto manufacturers (not just Toyota) are using these terms interchangeably to confuse consumers into thinking that their car has some new advance technology, when this technology has been on cars since the late 90's in Land Rover Discovery and Mercedes ML.

Rear locker locks the rear axle together into one solid rod...it ties the rear wheels together as if it was one wheel. One rear wheel turns...the other MUST too. Unlike ATRAC, rear locker binds if you make a turn on high traction surfaces (pavement). ATRAC is more flexible because it causes much less binding.