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Np246

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Old 01-26-2019, 10:53 PM
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Who in their right mind would put a clutch pack in a transfer case? I finally got around to checking out our 1999 Tahoe. We picked it up a year ago for $600. We were told the motor, trans and transfer case we're bad. Turns out the motor was fine with just a broke exhaust manifold. The trans was just the brake interlock. The transfer case was shot though. It had the pump rub hole in the case that led to burned up clutch pack. I replaced the transfer case today with a used one that has the case saver in it. I will be rebuilding the original though to keep as a spare.
 
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Old 01-27-2019, 12:24 AM
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From factory the front diff is just a hair lower in gear ratio than the rear. The difference lets the front pull just a little bit harder for traction, steering,ECT.
By having a clutch pack in the transfer case it relieves any bind that may occur in the drive train while driving in a no slip conditions such as dry pavement or lets say spotty ice patches with dry spots on a highway at hi-way speeds.
 
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Old 01-27-2019, 07:29 PM
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I'm pretty sure the clutch is just so the front drive can kick in automatically when it senses slippage at the rear.
 
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Old 01-28-2019, 04:32 PM
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Originally Posted by Tom A View Post
I'm pretty sure the clutch is just so the front drive can kick in automatically when it senses slippage at the rear.
Yes and No - Bear with me if I'm wrong.
With auto 4Wd there is a speed sensor on the front drive shaft - the computer systems senses the difference in speed between the front and rear driveshafts.
When the speed is different between the two and the rear has slippage the transfer case shift motor is activated by the computers and shifts into 4WD high. This can happen rapidly and depending on situation can be continually in and out.
By having a clutch pack incorporated in the transfer case it relives the shock of shifting along with the scenario in my first post.
Without a clutch pack in the system it could be in a constant bind and rapidly destroy itself.
 
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Old 01-28-2019, 04:40 PM
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There's a pulse width modulated solenoid that applies the clutch to whatever degree is necessary to make the front and rear wheel speed the same. I doubt it would be damaged otherwise, but it might ride "funny".
 
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Old 01-28-2019, 05:04 PM
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Yes the transfer case control module reads the rear vss and front output vss and when it senses rear wheel slip it engages the clutch pack to the front output. If the tccm or clutch pack fails though you have no 4x4 in auto, 4hi or 4 low. I bought the Tahoe knowing it had suspected transfer case problems. I was originally going to just swap in an np241 and I still might. The wife really likes the auto 4x4 though. In my opinion it is just more to go wrong. I have the front axle disconnect permanently engaged on my jimmy to eliminate that failure point.
 
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Old 01-28-2019, 05:25 PM
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Originally Posted by Tom A View Post
There's a pulse width modulated solenoid that applies the clutch to whatever degree is necessary to make the front and rear wheel speed the same. I doubt it would be damaged otherwise, but it might ride "funny".
Ok then I stand corrected in my old school theory
 

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