should the front driveshaft spin freely in 2h

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xxxt101:
hi i have a 2002 av 1500 4x4 should my front drive shaft spin freely when in 2h cause mine dont .

carnut:
from GM's service manual:


Front Drive Axle Description and Operation
Selectable Four Wheel Drive (S4WD) Front Axle Description and Operation
The Selectable Four Wheel Drive (S4WD) Front Axle consist of the following components:

      Differential Carrier Housing

      Differential Assembly

      Output Shafts (Left and Right Side)

      Inner Axle Shaft Housing

      Inner Axle Shaft (Right Side)

      Clutch Fork

      Clutch Fork Sleeve

      Electric Motor Actuator

The front axle on Selectable Four Wheel Drive model vehicles uses a central disconnect feature in order to engage and disengage the front axle. When the driver engages the 4WD system, the Transfer Case Control Module sends a signal to the electric motor actuator to energize and extend the plunger inside. The extended plunger moves the clutch fork and clutch fork sleeve across the inner axle shaft and the clutch fork shaft and locks the two shafts together. The locking of the two shafts allows the axle to operate in the same manner as a semi-floating rear axle. A propeller shaft connects the transfer case to the front axle. The differential carrier assembly uses a conventional ring and pinion gear set to transmit the driving force of the engine to the wheels. The open differential allows the wheels to turn at different rates of speed while the axle continues to transmit the driving force. This prevents tire scuffing when going around corners and premature wear on internal axle parts. The ring and pinion set and the differential are contained within the carrier. The axle identification number is located on top of the differential carrier assembly or on a label on the bottom of the right half of differential carrier assembly. The drive axles are completely flexible assemblies consisting of inner and outer constant velocity CV joints protected by thermoplastic boots and connected by a wheel drive shaft.

Transfer Case Description and Operation
The NVG 236/246 transfer case features a 4 button shift control switch located on the instrument panel. When the vehicle has the ignition key in the RUN position, the transfer case shift control module starts monitoring the transfer case shift control switch to determine if the driver desires a new mode/gear position. At a single press of the transfer case shift control switch, the lamp of the new desired position will begin flashing to inform the driver that the transfer case shift control module has received the request for a new mode/gear position. The lamp will continue to flash until all shifting criteria has been met and the new mode/gear position has been reached, or has been engaged. Once the new mode/gear position is fully active, the switch indicator lamp for the new position will remain ON constantly.

During normal driving situations the transfer case can operate in the Auto 4WD mode. In the Auto 4WD mode the transfer case shift control module monitors rear wheel slip speed, based on the inputs from both the front and rear propshaft speed sensors. When the vehicle experiences a rear wheel slip condition, the transfer case shift control module sends a pulse width modulated (PWM) signal to an electronic motor, which is the transfer case encoder motor. This motor rotates the transfer case sector shaft, applying a clutch pack. This clutch pack is designed to deliver a variable amount of torque, normally delivered to the rear wheels, and transfers it to the front wheels. Torque is then ramped up to the front wheels until the front propshaft speed sensor matches that of the rear propshaft speed sensor. Torque is then ramped down until torque is completely removed from the front wheels or until rear wheel slip is once again detected. The process would then repeat.

The NVG 236/246 transfer case has the added feature of also providing the driver with 3 manual mode/gear positions:

      4HI - 4 Wheel Drive high range

      2HI - 2 Wheel Drive high range

      4LO - 4 Wheel Drive low range

The driver may choose to select any of these mode/gear positions while driving the vehicle. However, the transfer case will not allow a shift into or out of 4LO unless the following criteria has been met:

      The engine is running.

      The automatic transmission is in Neutral, clutch depressed on manual transmissions.

      The vehicle speed is below 5 km/h (3 mph).

This transfer case also has a Neutral position. A shift to the Neutral position allows the vehicle to be towed without the rear axle rotating the transfer case main shaft and the transmission output shaft. Neutral position may be obtained only if the following criteria has been met:

      The key is ON.

      The automatic transmission is in Neutral, clutch depressed on manual transmissions.

      The vehicle speed is below 5 km/h (3 mph).

      The transfer case is in 2HI mode.

Once these conditions have been met, press and hold both the 2HI and 4LO buttons for 10 seconds. When the system completes the shift to neutral, the red neutral lamp will illuminate.

View the list of major components that make up the automatic transfer case (ATC) system below.

end of manual info.

From the info above, the front prop shaft is directly coupled to the differential carrier (via ring and pinion). what is unclear is if the carrier is permanently coupled to one inner axle shaft or not. if it is, then turning the prop shaft should turn one wheel only. if the carrier is NOT permanently coupled with one inner shaft, then turning the prop shaft will not turn either wheel, HOWEVER, it will cause the carrier to rotate inside the housing, and that would cause a certain amount of resistance felt at the prop shaft.

I've never looked at mine in operation, so i don't know the exact answer. but at least you should have a better understanding of what is happening in the different modes.

good luck. paul.

Wazbro:
I think that the front drive shaft is locked into the transfer case so it will only turn with the tranfer case.

If you had the back wheels off the ground and in 2hi you put it in gear the back wheels would turn and not the front wheels, but the front drive shaft would turn or in 2hi you could jack up the front wheels and turn them with out turning the front drive shaft.

dmcc1000:
I may be wrong here but I believe because we do not have manual locking hubs our shafts always spin? I notice that at low speed full wheel lock mine has the tell tale binding of the cv joints.

Den




carnut:


Quote from: dmcc1000 on 01/10/10 09:12 AM

I may be wrong here but I believe because we do not have manual locking hubs our shafts always spin? I notice that at low speed full wheel lock mine has the tell tale binding of the cv joints.

Den







The axle CV shafts will always turn with the tires. The end of the shaft has a spline that is locked into the front hubs, which in turn are bolted to the wheels. in 4wd the cv shafts are locked together internally and act as a solid shaft. The binding is caused by the different tracking radius between the front and rear axles during a turn.

Quote from: Wazbro on 01/10/10 07:36 AM

I think that the front drive shaft is locked into the transfer case so it will only turn with the tranfer case.

If you had the back wheels off the ground and in 2hi you put it in gear the back wheels would turn and not the front wheels, but the front drive shaft would turn or in 2hi you could jack up the front wheels and turn them with out turning the front drive shaft.


If you look at the operation description for the transfer case above, the front prop shaft is engaged by a clutch, so in 2wd, the transfer case does not drive the front prop shaft.





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