Toyota FJ Cruiser Forum

OK guys here is my situation. I got my FJ a few months ago and have done a few mods to it (3" Toytec Adj. Coil over front, Toytec 3" rear, Micky Thompson 285/75/r16 MTZ=33", Lucrum winch mount, and Warn 9.5ti). I wanted to see how it would perform and hooked up with a few Rising Sun guys and hit Old Chinaman Gulch here in CO. Everything went great, had the rear locked and the FJ went through everything well with one exception (V-notch obstacle) and got to check out the wench performance which was great as well. After V-notch I decided to try unlocking the rear and use only the A-trac for a while so I disengaged the rear locker (indication went out), engaged the A-trac (indication came on) and continued on the trail. we came upon another rocky area and I proceed to go over this obstacle in A-trac only, when I got opposing corners off the ground at which time both opposing tires started to spin with apparently NO A-trac being applied to the wheels with traction, I then re-engaged the rear locker and went right over.
Has anyone else had this happen? Could the A-trac not have been engaged with apparent panel indication that it was? I have not had the chance to recreate the situation yet but hopefully will in the next few weeks, I might just take the FJ to the dealer and have them verify that the A-trac system is working properly.. If you have any suggestions what might have happened it would be greatly appreciated..
Thanks, PhatFJ

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General

When the transfer shift lever is L4 or LL position and A-TRAC switch is turned on, the A-TRAC helps
restrain wheelspin by controlling the brake fluid pressure that is applied to the spinning wheels, and
distributes the drive force that would have been lost through the slippage to the remaining wheels in order
to achieve an effect that is similar to LSD.

of the slippage at the wheels, as detected by the Skid Control ECU.

Effectiveness of A-TRAC

The effectiveness of A-TRAC is as follows:

Off-road drivability that is equivalent to having the center differential locked and limited slip
differentials on both front and rear has been realized.

This function makes the operation of the differential lock switches basically unnecessary to ensure the
ease of driving.

A-TRAC allows for drivability benefits similar to those of locked differentials, while still allowing for
the vehicle to be steered at low speeds, without the binding that would normally be associated with locked

differentials.

You didn't say whether you were in L4 or LL?

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Squid: Thanks for the reply!! I was definitely in LL, never took it out on this trail. I understand the theory of the A-trak system, this is why I was so surprised that both opposing corners were spinning with all indications that it was on..

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I just thought I'd post the info for others not famialiar with the A-trak system.

The way it works is when, say the right wheel spins, the brakes automatically apply enough pressure to slow the spinning wheel down to almost the same speed as the none slipping left wheel. By doing that torque is supposed to tranfser to the wheel with traction so the wheel off the ground will still spin.
My Nissan Titan has the same thing but it's called ABLS (Active Brake Limted Slip)

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Thanks, It would seem then that the torque available to the wheels which did have traction was not enough to get me over the rocks I was on. Very interesting!!

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It's really just to help in slick conditions and not designed for climbing so a lot of us upgraded our rear ends to the Trutrac, even owners of trucks with the E-locker.. Detroit Truetrac - Eaton.com

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