clarity on the awd system
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Cadillac STS Forum - 2005 through 2012 Discussion, clarity on the awd system in Past Cadillac Vehicle Discussion; Exactly how does the awd system in the STS work. I've read many treads and haven't gotten a clear answer. ...
  1. #1
    B1n2fra's Avatar
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    clarity on the awd system

    Exactly how does the awd system in the STS work. I've read many treads and haven't gotten a clear answer. It says its not all time all wheel drive and that it works with the traction control and stability systems. It says when the system detects wheel spin it cuts power to that wheel and applies it to the wheel or wheels with traction. OK so how is it that from jump 0 to 60 the car doesn't spin the rear wheels its just maybe sometimes chirp the wheels and flys off the line. Does the awd kick in when a certain amount of throttle is applied or what. If anyone with any knowledge of this system please answer I would really like to know about this system in detail. I also read that it has a open center differential and a slightly smaller size wheel on the front wouldn't cause a problem ( do not try)..

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    dkozloski's Avatar
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    Re: clarity on the awd system

    It's a completely open system with three open(non-posi) differentials. Wheelspin is controlled by the traction system that can pull ignition timg as well as throttle position to reduce torque to the drive wheels and the spinning wheel is also controlled by application of braking on that wheel with ABS. The front and rear wheel/tire combinations have the same tire circumference so that is not a factor. The drive train is connected all the time and the traction control system operates when required. The center differential is planetary and supplies 40% of the drive to the front wheels and 60% to the rear.
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    Quote Originally Posted by dkozloski
    It's a completely open system with three open(non-posi) differentials. Wheelspin is controlled by the traction system that can pull ignition timg as well as throttle position to reduce torque to the drive wheels and the spinning wheel is also controlled by application of braking on that wheel with ABS. The front and rear wheel/tire combinations have the same tire circumference so that is not a factor. The drive train is connected all the time and the traction control system operates when required. The center differential is planetary and supplies 40% of the drive to the front wheels and 60% to the rear.
    I was talking about wheel and tire combinations of different circumferences. And that doesn't explain how sometimes on wet surfaces the rear wheels spin untill the traction steps in and sometimes if the front wheels are on an ice patch and the rear on dry pavement the front would spin until the traction steps in. Is it all the time all wheel drive or just whenever the situation needs it o be

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    Re: clarity on the awd system

    Mismatched wheel and tires sizes could cause additional wear to the center differential. Because the AWD system has three open differentials, any single wheel is free to spin at any time if the tire has little or no traction. The wheel/wheels that spin are controlled by the traction control system which is always operational unless turned off. With this AWD system just apply power with the throttle. If wheel/wheels spin, don't back off on the power. The system will automatically reduce engine power and apply sufficient braking to the spinning wheel that as much torque as can be utilized will be applied to the other wheels. If all the wheels have poor traction you aren't going anywhere.
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    Re: clarity on the awd system

    Koz is correct. It's full time and slip is controlled via the stabilty control (like F1 cars but not as fast acting). OEM tires are all virtually the same circumference; vary from this at your own risk.

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    Re: clarity on the awd system

    So if I turned off the traction and stability all four wheels would spin on a patch of ice or snow. And why is it that when the traction is on the rear wheels would spin and the front wouldnt do anything untill the traction kicked in.

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    Re: clarity on the awd system

    Quote Originally Posted by B1n2fra View Post
    So if I turned off the traction and stability all four wheels would spin on a patch of ice or snow. And why is it that when the traction is on the rear wheels would spin and the front wouldnt do anything untill the traction kicked in.
    If you turn off traction control and stability only the wheel with the least traction would spin like crazy and the rest would just sit there doing nothing. Turn the stuff back on and the spinning wheel would stop and the rest would start to pull.
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    Quote Originally Posted by dkozloski
    If you turn off traction control and stability only the wheel with the least traction would spin like crazy and the rest would just sit there doing nothing. Turn the stuff back on and the spinning wheel would stop and the rest would start to pull.
    So how is it all time awd if the other wheels just sit while one spins. Shouldn't they all be making some sort of forward motion

    ----------

    And is it true that the cts awd is different from the sts and srx

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    Re: clarity on the awd system

    Quote Originally Posted by B1n2fra View Post
    So how is it all time awd if the other wheels just sit while one spins. Shouldn't they all be making some sort of forward motion

    ----------

    And is it true that the cts awd is different from the sts and srx
    Don't turn traction control and stability off and you're good to go. It's all part of the AWD system. No wheel will spin freely and they will all pull, all the time.
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    Re: clarity on the awd system

    As far as staggered wheel set-ups on AWD cars (I believe the op mentioned it), the rule of thumb, at least for most AWD systems is as long as the rolling diameter is < 2% difference between the front and back, it will not affect the diff.

    Go over to audizine and see what happens when people run staggered setups over 2% difference on AWD.

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    Re: clarity on the awd system

    If your AWD vehicle has any type of limited slip differentials they will be ripped with differing tire sizes.

    ----------

    It's easy to understand the mysteries of AWD if you drive your car around on the fresh snow in a parking lot, then get out and look at the tracks. Because of suspension and steering geometry every wheel will make a separate track in a tight turn, every wheel rolls the turn at a different radius, and thus at a different speed. No two wheels can be locked and be forced to turn together at the same speed. That explains the need for the center differential as well as the front and rear.

    4WD vehicles don't have the center differential and that is why you must throw them out of 4WD on a paved road or risk rapid tire wear or driveline damage.
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    Re: clarity on the awd system

    It's been reported that even after pressing & holding the Console's TC button for over 5 seconds, the AWD's still have some stabilty control active to prevent car-damaging wheel spin.

    So far, I've never had a need to turn off traction control.

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    Re: clarity on the awd system

    There are two separate systems involved. Traction Control(TC) which controls wheelspin and the Stability Augmenatation System that aids control during slides, skids, and spins. They share some of the same components but operate independently.
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    Re: clarity on the awd system

    Quote Originally Posted by EChas3 View Post
    ...So far, I've never had a need to turn off traction control.
    It's not a case of 'need', but 'want'. Sometimes I just want to hit the gas and not care if it slips a little. Unless it's raining/snowing I usually turn it fully off (hold button until 'stability system off' in DIC).

    The first time I was caught by the reduced-power-to-regain-control mode was coming out of a business onto a busy road with a relatively narrow opening in traffic. A little loose dirt/gravel at the edge of the road let the rear end get 'free' and I about dropped a load as the car went into recovery mode while traffic bore down on my rear end. I was expecting the slip and to then take off once the wheels caught on the main surface. Didn't happen that way. With stability off it does exactly what I expected in that situation.

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    Re: clarity on the awd system

    Quote Originally Posted by MacMuse View Post
    It's not a case of 'need', but 'want'. Sometimes I just want to hit the gas and not care if it slips a little. Unless it's raining/snowing I usually turn it fully off (hold button until 'stability system off' in DIC).

    The first time I was caught by the reduced-power-to-regain-control mode was coming out of a business onto a busy road with a relatively narrow opening in traffic. A little loose dirt/gravel at the edge of the road let the rear end get 'free' and I about dropped a load as the car went into recovery mode while traffic bore down on my rear end. I was expecting the slip and to then take off once the wheels caught on the main surface. Didn't happen that way. With stability off it does exactly what I expected in that situation.
    It's like God taking away the car keys because you drove like hell in traffic.
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