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Thread: transfer case differences

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    Default transfer case differences

    The new 4x4 sequoia uses the JF3A T-case. How does it differ mechanically from the VF4AM in older Sequoia's? Both are part time systems. Are they both gear driven?

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    Default Re: transfer case differences

    Quote Originally Posted by ron717 View Post
    The new 4x4 sequoia uses the JF3A T-case. How does it differ mechanically from the VF4AM in older Sequoia's? Both are part time systems. Are they both gear driven?
    The JF3A is both a full time 4wd t-case (4wd Hi) and a part time t-case (4wd Hi locked and 4wd lo). Unlike the older T-case, the new one includes a Torsen limited slip mechanical differential which transfer 30% of the engine's power all the time (4wd hi) to the front wheels until there is slippage at the rear wheels.

    If slippage occurs at the rear wheels then the Torsen mechanically transfers upto 50% of the power to the front wheels. Unlike the older Sequoia t-case (and the current Tundra's part time t-case) it does not rely on the brakes to transfer power from rear to front when the rear wheels slip.

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    Default Re: transfer case differences

    The Sequoia was introduced in 2001 and had the VF3AM Transfer Case which was both full and part time 4WD. It had an open center differential that could be locked. In 2005 they started using the VF4AM Transfer Case which was both full and part time, but it has a torsen center differential. Power is split 40% front and 60% rear under normal driving, and can send up to 53% to the front and 71% to the rear during slip. For 2008 they now use the JF3A Transfer Case, which has the same torsen center diff, but is a lot stronger to handle 381 horse and 401 torque. Toyota had to change the transfer case for the Land Cruiser, LX570,Sequoia, and Tundra, all because of the new 5.7 V8. The Tundra uses the JF1A which is part time only, the Land Cruiser,LX570 use the JF2A, which has no 2WD option, but also has a torsen center diff.

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    Default Re: transfer case differences

    I'm not seeing how a center diff with a torsen can be anything but "full time" and "locked". "Part time" means the front drive shaft can be completely disengaged.

    Michael

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    Default Re: transfer case differences

    Quote Originally Posted by Michael2000 View Post
    I'm not seeing how a center diff with a torsen can be anything but "full time" and "locked". "Part time" means the front drive shaft can be completely disengaged.

    Michael
    Not true, part time means locked front & rear diff via t-case, equal power to both axles. Full time is a torsen setup with different percentage of torque to either axle. Ours is bot. Full time its torsen, and when you lock center diff, it becomes part time.
    08 Sequoia SR5, nautical blue, 5.7 V8, tow pkg

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    Default Re: transfer case differences

    ron717,
    Great detailed explanation. I've had multiple 4wd rigs, full and part time, and appreciate your detailed and understandable discription of the Sequoia system.

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    Default Re: transfer case differences

    Quote Originally Posted by ron717 View Post
    Not true, part time means locked front & rear diff via t-case, equal power to both axles. Full time is a torsen setup with different percentage of torque to either axle. Ours is bot. Full time its torsen, and when you lock center diff, it becomes part time.
    I don't know where you come up with this. There is no part time about it. It is always drving all four wheels, whether locked or not. It could be this is just another one of these dumb layman's terms that people have now accepted. I'm going to go with the engineers, such as those at American Axle and Manufacturing. They call their transfer cases with Full Time 4WD with locking, Full Time.

    Michael

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    Default Re: transfer case differences

    Quote Originally Posted by Michael2000 View Post
    I don't know where you come up with this. There is no part time about it. It is always drving all four wheels, whether locked or not. It could be this is just another one of these dumb layman's terms that people have now accepted. I'm going to go with the engineers, such as those at American Axle and Manufacturing. They call their transfer cases with Full Time 4WD with locking, Full Time.

    Michael
    Part time and full time refers to being able to drive on paved surfaces, not how a vehicle is putting power to the ground. Full time means you can use it on a paved surface, part time means only use it on dirt or in snowy and icy conditions.

    This nomenclature has been used for decades.

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    Default Re: transfer case differences

    Quote Originally Posted by TJeeper View Post
    Part time and full time refers to being able to drive on paved surfaces, not how a vehicle is putting power to the ground. Full time means you can use it on a paved surface, part time means only use it on dirt or in snowy and icy conditions.

    This nomenclature has been used for decades.
    Yes, I know, but Ron seems to have his own definitions.

    Michael

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    Default Re: transfer case differences

    Quote Originally Posted by TJeeper View Post
    Part time and full time refers to being able to drive on paved surfaces, not how a vehicle is putting power to the ground. Full time means you can use it on a paved surface, part time means only use it on dirt or in snowy and icy conditions.

    This nomenclature has been used for decades.
    Exactly, and as I stated before part time is locked between front & rear. Its called part time because it can only be driven on loose surfaces such as snow, gravel or mud. Full time 4WD is can be used on any surface just like in 2WD.

    On the new Sequoia full time is Torsen 4Hi, when diff-lock is not engaged only. Then when diff-lock is engaged in 4Hi, it becomes part time, no longer Torsen.

    Its not being driven on 4 wheels all the time, unless its a true 4WD with both mechanical locking front & rear diffs along with drive shaft locked between front and rear.
    Last edited by ron717; 10-30-2008 at 06:49 AM.
    08 Sequoia SR5, nautical blue, 5.7 V8, tow pkg

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    Default Re: transfer case differences

    Quote Originally Posted by ron717 View Post
    Exactly, and as I stated before part time is locked between front & rear. Its called part time because it can only be driven on loose surfaces such as snow, gravel or mud. Full time 4WD is can be used on any surface just like in 2WD.

    On the new Sequoia full time is Torsen 4Hi, when diff-lock is not engaged only. Then when diff-lock is engaged in 4Hi, it becomes part time, no longer Torsen.

    Its not being driven on 4 wheels all the time, unless its a true 4WD with both mechanical locking front & rear diffs along with drive shaft locked between front and rear.
    The "simplest" (or not) way to describe the Sequoia's T-case is as both full time and PT 4wd, depending on the driver's needs. Its a full time T-case when operating in 4wd high. Power is distributed across the rear wheels via A-trac (ABS system) and between the front and rear tires via the Torsen ctr differential. Because Torsen is a mechnical limited slip differential, it can force a minimum amount of engine torque to the front wheels at all times, when engaged. This essentially qualifies the Sequoia as an AWD vehicle when operated in 4wd Hi.

    The statement above is incorrect in stating "Its not being driven on 4 wheels all the time". In fact when operated in 4wd Hi there is "always" a minimum amount (30%) of the engine power delivered to the front tires at all times. This is directly attributed to the LSD capabilities of the Torsen. What allows it to operate on dry pavement is that the torque is managed from front to rear from a minimum of 30% upto 50%. This flexibility in power transfer enables the Sequoia to have power all the time to the front tires and not bind on dry pavement when operating in 4wd Hi.

    There are many auto makers that call their 4wd systems "full-time" however these do not always meet the definition of AWD. The difference between AWD and Full-time is that AWD means there's always power to the front tires at all times. Full-time can be the same as AWD however it doesn't have to be. There are many full-time 4wd systems that do not deliver any power to the front wheels until the rear wheels slip. Not as good a system as AWD but capable of operating on dry surfaces, ie Full-time.

    The Sequoia is also a PT 4wd system when operated in 4wd Hi with the ctr differential locked. When the system is in this configuration the drivetrain forces 50% of the power to the front wheels and the other half to the rear wheels...all the time. Good for slippery conditions but should not be operated on dry pavement.

    Of all the 4wd drivetrains in the Toyota line-up the Sequoia offers the greatest flexibility. Its not available in any other Toyota vehicle with the 5.7 engine. The Sequoia offers 2wd, 4wd hi, 4wd hi ctr locked, 4wd Lo and 4wd Lo ctr locked.

    The only upgrade that could make the system better would be a mechanically locking or limited slip differential in the rear which is currently an open rear differential managing wheel slippage by using the rear ABS electronics to transfer torque when wheel slippage occurs.
    Last edited by Heatwave3; 10-31-2008 at 09:39 AM.

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    Default Re: transfer case differences

    Can ATRAC be fully deactivated? Some systems will not allow the safety nannies to be fully shut down. In some instances such as mud or snow you want to be able to spin the tires. My wife's old AWD XC90 would shift power so much on hard pack snow that it never went anywhere. Just alot of noises. I am looking at either the Sequoia or a 100 series LC. I like the space of the Sequoia over the LC but the LC has the wheel-ability factor. So, can you spin the tires if you want?

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    Default Re: transfer case differences

    Quote Originally Posted by Ryan818 View Post
    Can ATRAC be fully deactivated? Some systems will not allow the safety nannies to be fully shut down. In some instances such as mud or snow you want to be able to spin the tires. My wife's old AWD XC90 would shift power so much on hard pack snow that it never went anywhere. Just alot of noises. I am looking at either the Sequoia or a 100 series LC. I like the space of the Sequoia over the LC but the LC has the wheel-ability factor. So, can you spin the tires if you want?
    Yes...the stability software and the A-trac software can be deactivated. Once these have been deactivated (they each have their own switch) then the A-LSD will be activated (there's actually a light on the console that shows A-LSD is still engaged).

    This means the ABS software is still managing slippage from left to right across the rear wheels (the Sequoia as well as the LC and LX570 all have open rear differentials). Upto (I believe 35 mph) the ABS software will engage to brake the wheel in the rear that is slipping to automatically move torque to the wheel that's not slipping.

    The "wheel-ability" factor is nearly identical between the new model Sequoia and the new model LC and LX. They have the same engine and nearly the same drivetrain. The primary difference between the LC and Sequoia drivetrain is that you'll give up 2wd in the LC/LX but gain the "Hillclimb" software that allows the vehicle to maintain ultraslow speeds.

    For the benefit of giving up 2wd and gaining "hillclimb" you'll have the pleasure of forking over an extra $15-25K. You be the judge if its worth it.

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    Default Re: transfer case differences

    Thanks. Is there an aftermarket rear locker available for the Sequoia?

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    Default Re: transfer case differences

    Quote Originally Posted by Ryan818 View Post
    Thanks. Is there an aftermarket rear locker available for the Sequoia?
    I don't believe so or at least I've not been able to find one. There are rear LSDs and lockers for the Tundra however since it has a solid rear axle vs the Sequoia's IRS, it would not be useable in the Sequoia.

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