4x4 / Off-Road TechThis section contains all discussion related to taking the FJ Cruiser in Off-Road situations, 4x4 applications and any armor modifications.
I justed called my Dealer to see how the back order for the switches was going. The back order report from Toyota stated the switches were being shipped 5/10 and should be in Torrence, CA on 5/12. From there the switches will be mailed to each dealer.
Wolfbak - I have the same concerns you do about the hack of the ATRAC with engaged rear locker. If someone has worked through this scenario of both working at same time, then maybe there is a way:
1. 4x4 low range ATRAC engaged means sensors look for wheel slip and apply brake pulses to transfer traction to non-slipping wheel.
2. Rear locker engaged means both rear wheels turn at same revolutions per minute, no exceptions.
Now you are wheeling up a rock and one of the front wheels comes off the ground (say right front for sake of argument), and at the same time both rear wheels momentarily break traction to push the vehicle forward. What this means is the slowest turning wheel is the left front, because the right front is clawing at air and the rear wheels have slipped as they broke traction.
If I understand things correctly, then ATRAC reacts to brake the slipping wheels (sensors in this case detect 3 wheels slipping) without reducing engine power. Sending braking pulse signals to three wheels cannot be good for a locked different. Also, I assume that the ECU must be reprogrammed to ignore the slippage in the rear wheels when locked.
If I've missed something, I truly would appreciate understanding how someone plans to hack the ECU to make ATRAC work with the rear locker engaged.
Thought I'd add a little to this.
If one front wheel is in the air and the rear wheels are slipping you would have three different RPMs. The front tire in the air would move at twice the RPM as the rear, the front tire on the ground would not move at all.
The ATRAC can (theoretically) only work across the axle. If you brake both wheels on the same axle (even without a locked rear differential) in 4WD, no matter the circumstances, the engine slows down. If you somehow manage to have the front tires on the ground and the rear tire in the air ATRAC will not brake the rear because it will be moving at the same speed as the front wheels.
Pulsing should not cause sustained binding like driving on a dry surface doing circles will. If for some reason the brakes are applied (even unevenly) it would not be an overwhelming force that snaps the axle. If this were the case the transfer case, which sees an unequal amount of force when the brakes are applied (because the front brakes are smaller than the rears), would regularly snap. Not the case.
Thanks Matt. I realized reading Thai's post this morning that my earlier assumptions did not recognize that the speed sensors are just across the axle, not sensing all four wheels. The explanations from you and Thai have been very helpful and written so even I can understand. I appreciate your patience with my slow comprehension of the forces at work here.
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