2001 Suburban

[varmint2506]

I was wondering if the front drive shaft should turn freely or not turn at all when in two wheel drive. I noticed the other day that mine was turning while in 2 Hi. Both my '97 and '98 are totally disengaged while not in 4x4. Does this have something to do with the "Auto 4x4" on the 2001 and newer models? Seems like it would put more wear and tear on the front U joints if it is supposed to be engaged all the time.

 

As always,

[mmmikkke]

The "auto 4x4" mode would engage and disengage the front differential; the quick engagement required would preclude spontaneously engaging both the transfer case *and* the front differential at the same time. So if you can't turn off "auto 4x4", this is probably why the front driveshaft remains engaged at the transfer case.

[bobcat5544]

it will turn even in 2hi, but you should still be able to turn it by hand also

[varmint2506]

So if you can't turn off "auto 4x4", this is probably why the front driveshaft remains engaged at the transfer case.

 

<{POST_SNAPBACK}>

 

 

 

It does have 2 Hi, which is what is puzzling me. I would think while in 2 Hi nothing would turn up front, including the drive shaft. Local dealer was not sure of the answer either. They thought this may have changed when GM changed the transfer case design.

[mmmikkke]

Just to close the loop, I'd get your salesman go with you out to the lot so you can crawl under another (brand new) truck with the same transfer case and see if its front driveshaft doesn't turn also. I'd do this because maybe your transfer case is not disengaging like it's supposed to.

[bobcat5544]

So if you can't turn off "auto 4x4", this is probably why the front driveshaft remains engaged at the transfer case.

 

<{POST_SNAPBACK}>

 

 

 

It does have 2 Hi, which is what is puzzling me. I would think while in 2 Hi nothing would turn up front, including the drive shaft. Local dealer was not sure of the answer either. They thought this may have changed when GM changed the transfer case design.

 

<{POST_SNAPBACK}>

 

 

 

 

put it in 2hi, get under the vehicle grab the shaft if it turns then it is fine, if it doesn't then you need to disconnect it from the transfer case and try to turn it if it does not turn freely then the front diff actuator is keeping it engaged, but if it does turn freely then reconnect it and do the oppisite to the transfer case, if it is locked then the transfer case clutch assm is haveing some type of problem

 

the reason why it would turn while driving and still trun freely while not moveing is due to the clutch assm in the tranfer case which you shouldn't be concerned with

[Bish]

The front driveshaft normally turns when driving in 2HI. It is only due to friction from the fluids. It should spin by hand.

[z85]

I want to know for sure too.

But no one seems to know.

 

Check out this post and see what you think.

 

http://www.gm-trucks.com/forums/index.php?...ront+driveshaft

 

 

Z85

[bobcat5544]

Info on how this tranfer case works with auto 4x4, 4x4hi, 4x4lo,2hi, and Neutral modes

 

Transfer Case Description and Operation

General Operation

The New Venture Gear model NVG 246 RPO NP8 transfer case is a two speed automatic, active, transfer case. The NVG 246 transfer case has many changes from prior years. The NVG 246 is now classified as an Electronic Architect Upgrade (EAU). The upgrades to the NVG 246 EAU include some of the following internal changes:

 

A new encoder motor for faster operation in the AWD mode.

The control actuator lever (3) is a new design with different cam angles.

The shift detent plunger and spring is no longer used.

The clutch assembly (1) uses a new style return spring and clutch washer.

A new rear output shaft (2) no longer uses a retaining ring by the oil pump.

The range shift fork (4) is a newer design.

The NVG 246 EAU provides 5 modes, Auto 4WD, 4HI, 4LO, 2HI and Neutral. The Auto 4WD position allows the capability of an active transfer case, which provides the benefits of on-demand torque biasing wet clutch and easy vehicle tuning through software calibrations. The software calibrations allow more features such as flexible adapt ready position and clutch preload torque levels. The technology allows for vehicle speed dependent clutch torque levels to enhance the performance of the system. For example, the system is calibrated to provide 0-5 ft lb of clutch torque during low speed, low engine torque operation, and predetermined higher torque for 40 km/h (25 mph) and greater. This prevents crow-hop and binding at low speeds and provides higher torque biases at higher vehicle speeds, in order to enhance stability.

 

Transfer Case Shift Control Switch

The NVG 246 EAU transfer case features a 4 button shift control switch located on the instrument panel. When the ignition key is in the RUN position, the transfer case shift control module monitors the transfer case shift control switch to determine if the driver desires a new mode/range 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/range position. The lamp will continue to flash until all shifting criteria has been met and the new mode/range position has been reached, or has been engaged. Once the new mode/range 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 control actuator lever 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 ramped up to the front wheels until the front propshaft speed sensor matches that of the rear propshaft speed sensor. Torque is ramped down to the front wheels. The process would repeat if rear wheel slip is detected again.

 

The NVG 246 EAU transfer case has the added feature of also providing the driver with 3 manual mode/range 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/range 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.

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 rotating the transmission output shaft. Neutral position may be obtained only if the following criteria has been met:

 

The engine is running.

The automatic transmission is in Neutral.

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.

 

The NVG 246 EAU case halves are high-pressure die-cast magnesium. Ball bearings support the input shaft, the front output shaft, and the rear output shaft. A thrust bearing is located inside of the input shaft gear to support the front of the rear output shaft. The transfer case requires Auto Trac® II Fluid GM P/N 12378508 (Canadian P/N 10953626) which is blue in color. The fluid is designed for smooth clutch application. An oil pump, driven by the rear output shaft, pumps the fluid through the rear output shaft oil gallery to the clutch and bearings.

 

There are two versions of the NVG 246 EAU, which depend on the transmission applications and vehicle applications. If the vehicle is equipped with a transmission RPO M30, the transmission splines in the input gear will have 27 teeth. With this application the planetary carrier assembly will have 4 pinion gears. If the vehicle is equipped with transmission RPO MT1 or MN8, the transmission splines in the input gear will have 32 teeth. The planetary carrier assembly on this application will have 6 pinion gears.

 

2WD Power Flow

When the NVG 246 EAU is in the 2HI mode, the power flows from the transmission (1) to the input shaft gear (2). The input shaft gear (2) is connected to the rear output shaft (4) by the high/low range collar (3). The range collar (3) outer teeth are engaged with the input shaft gear (2) inner, high-speed position teeth. At the same time the range collar is slip splined to the rear output shaft (4). The rear output shaft (4) delivers the power flow to the rear propshaft (5). The position of the control actuator lever shaft (7) allows no clutch (6) engagement. The high/low range shift fork (8), is in the high-speed position on the control actuator lever shaft (7).

 

4HI and AWD Power Flow

In the 4HI mode, the power flow to the rear propshaft (10) is the same as it is in the 2HI mode. To deliver power flow to the front propshaft (13) during the 4HI position, the transfer control module commands the encoder motor (15) to apply the clutch to a calibrated torque. The encoder motor (15) turns the control actuator lever shaft (14). A brake in the encoder motor (15) holds the control actuator lever shaft (14) in the full clutch position. The control actuator lever shaft (14) is cam designed and the cam action moves the clutch lever (4). The clutch lever (4) pivots on the clutch lever pivot studs and moves toward the clutch apply plate, to engage the clutch. As more pressure is applied to the clutch apply plate, the clutch discs are compressed. Using inner clutch discs, which are engaged with the clutch hub (5), and the outer clutch discs, which are engaged with the clutch housing (6), the power flow is delivered to the clutch housing (6). The clutch hub (5) is splined to the rear output shaft (9), and the clutch housing (6) rotates on a needle bearing on the rear output shaft (9). The chain drive sprocket (7) is splined to the clutch housing (6). The power flows from the drive sprocket (7), through the chain (11), to the chain driven sprocket. The driven sprocket is splined to the front output shaft (12). The power flow is delivered to the front propshaft (13) through the front output shaft (12).

 

During the Auto 4WD mode, the power flow is the same as it is in the 4HI mode. Except, during the Auto 4WD mode, the encoder motor (15) rotates the control actuator shaft lever (14) to the correct torque level positions. Rotating the control actuator (14) to the various positions changes the clutch torque level. When a difference of front propshaft (13) to rear propshaft (10) speed is recognized, the transfer case control modules command for more, or less clutch torque.

 

4LO Power Flow

When shifting the transfer case to the 4LO mode, it commands the encoder motor (9) to turn the control actuator lever shaft (8), to move the high/low range shift fork (10). The shift fork (10) moves the high/low range collar (6), which is slip splined on the rear output shaft (7) toward the rear of the transfer case. The range collar (6) outer teeth disengage from the input shaft gear (2) inner teeth. The range collar (6) outer teeth then engage in the planetary carrier (5) teeth. The power flow is now from the input shaft gear (2) planetary teeth to the planetary gears (3) in the carrier. Rotating the planetary gears (3), which are engaged in the annulus gear (4), the planetary carrier (5) rotates. The planetary carrier (5) engaged to the range collar (6), drives the rear output shaft (7), providing a 2.72:1 reduction to the speed of the rear output shaft (7). The power flow to the front propshaft is the same as it is in the 4HI.

 

A neutral position is obtained when the range collar (6) is not engaged to the input shaft gear (2) or the planetary carrier (5). Neutral position is used for towing the vehicle.

 

Service 4WD Indicator

The Service 4WD indicator is an integral part of the cluster and cannot be serviced separately. This lamp is used to inform the driver of the vehicle that a transfer case system malfunctioned. The Service 4WD indicator is controlled by the transfer case shift control module via Class 2.

 

Transfer Case Encoder

The encoder is mounted to the transfer case motor/encoder assembly and is replaced as an assembly. The encoder converts the shift detent lever shaft position, representing a mode or range, into an electrical signal input to the transfer case shift control module. The module detects what position the transfer case is in by monitoring the voltage returned on the encoder signal circuit. This voltage translates into AUTO 4WD, 2HI, 4HI, NEUTRAL, and 4LO or in transition between gears.

 

Transfer Case Motor/Encoder

The transfer case motor/encoder consists of a permanent magnet (PM) DC motor and gear reduction assembly. It is located on the left hand side, driver's side, of the transfer case. When activated, it turns the shift detent lever shaft of the transfer case, clockwise or counterclockwise, to shift the transfer case. The motor/encoder is controlled with a pulse width modulated (PWM) signal by the transfer case shift control module. This circuit consists of a driver on both the Motor A and Motor B circuits. The encoder motor is bi-directional in order to allow the motor to shift the transfer case from 2HI or 4HI to NEUTRAL and 4LO positions.

 

Transfer Case Motor Lock

The transfer case motor lock is used to provide a 2HI, 4HI, and 4LO lock-up feature. When the lock circuit is energized, the transfer case encoder motor is allowed to turn. When the transfer case is placed 2HI, 4HI, or 4LO the motor lock circuit is de-energized and the lock is applied. This assures that the transfer case remains in the current gear position until a new gear position is requested. When AUTO is selected, the motor lock remains applied until an adaptive mode, torque being applied to the front propshaft, is required. During an adaptive mode the motor lock circuit is energized and the motor lock is released, enabling the encoder motor to turn and apply or release torque at the front propshaft.

 

Transfer Case Shift Control Module

The transfer case shift control module uses the VIN information for calculations that are required for the different calibrations used based on axle ratio, transmission, tire size, and engine. The system does not know which calibration to use without this information. When the vehicle is in the AWD mode, the transfer case shift control module monitors the speed of the front and rear propshaft, in order to detect wheel slippage. When wheel slippage is detected, the module applies a clutch pack contained inside the transfer case. This clutch pack is used to lock-in and apply the front propshaft, transferring torque to the front wheels. The clutch pack is applied by a motor/encoder assembly. When slip is no longer detected by the transfer case shift control module, the clutch is no longer applied.

 

Transfer Case Speed Sensors

There are three speed sensors on the automatic transfer case (ATC), two on the rear output shaft and one on the front output shaft. Each speed sensor is a permanent magnet (PM) generator. The PM generator produces a pulsing AC voltage. The AC voltage level and number of pulses increases as speed increases.

 

Vehicle Speed Sensor - One of the two speed sensors on the rear output shaft is the vehicle speed sensor (VSS) input to the powertrain control module (PCM). The PCM sends this information to the transfer case shift control module via the Class 2 serial data bus.

 

Rear Propshaft Speed Sensor - The transfer case shift control module converts the pulsating AC voltage from the rear transfer case speed sensor to a rear propshaft speed in RPM to be used for calculations. The rear propshaft speed can be displayed with a scan tool.

 

Front Propshaft Speed Sensor - The transfer case shift control module converts the pulsating AC voltage from the front transfer case speed sensor to front propshaft speed in RPM to be used for calculations, and to monitor the difference between the front and rear sensor speed. It is also used in the AUTO, Adapt, mode to determine the amount of slip and the percent of torque to apply to the front axle. The front propshaft speed can be displayed with a scan tool.

[z85]

bobcat5544

 

 

EXCELLENT!!!

 

Now I know what I have under my 2001 Surban 2500 8.1, MT1, 4.10s

 

Didn't know they made 2 versions...

 

Thanks!!

 

Z85

[bobcat5544]

bobcat5544

 

 

EXCELLENT!!!

 

Now I know what I have under my 2001 Surban 2500 8.1, MT1, 4.10s

 

Didn't know they made 2 versions...

 

Thanks!!

 

Z85

 

<{POST_SNAPBACK}>

 

 

 

there are a few different tranfercases

NVG 261 transfer case is available in 5 variations

NVG 236/246 transfer case features a 4 button shift control switch (auto 4x4)

NVG 263 transfer case features a three button shift control switch

NVG 149 RPO NP3 is a single speed, single mode transfer case. The mode is full-time all wheel drive

[varmint2506]

So if you can't turn off "auto 4x4", this is probably why the front driveshaft remains engaged at the transfer case.

 

<{POST_SNAPBACK}>

 

 

 

It does have 2 Hi, which is what is puzzling me. I would think while in 2 Hi nothing would turn up front, including the drive shaft. Local dealer was not sure of the answer either. They thought this may have changed when GM changed the transfer case design.

 

<{POST_SNAPBACK}>

 

 

 

 

put it in 2hi, get under the vehicle grab the shaft if it turns then it is fine, if it doesn't then you need to disconnect it from the transfer case and try to turn it if it does not turn freely then the front diff actuator is keeping it engaged, but if it does turn freely then reconnect it and do the oppisite to the transfer case, if it is locked then the transfer case clutch assm is haveing some type of problem

 

the reason why it would turn while driving and still trun freely while not moveing is due to the clutch assm in the tranfer case which you shouldn't be concerned with

 

<{POST_SNAPBACK}>

 

 

 

 

The issue of it not turning freely by hand is what I was concerned with. The front actuator is working ok I checked that by jacking up the front and spinning the wheels. They spin freely while in 2hi and lock when in 4hi. One dealer said it should turn freely and the other said the TC keeps it locked. I need to test on another 2001...

 

Thanks for the help!

[Rensch100]

Ive been a master tech for 15 years, worked at gm dealer 8 years and now firestone. I have rebuilt many 246 transfer cases. Your front drive shaft with the 246 will always turn. You probally won't even be able to turn it by hand. Stick a bar in the ujoint and you will be able to turn it. There is a certain amount of preload on the clutch disk, and it is there for a reason. If the shaft did not turn in 2wd, the disk would constanly have friction and wear out very quickly. It would be like riding the clutch on a strait stick all day long. On most transfer cases in 2wd if the shaft does not turn in 2wd or you cannot spin the shaft you may have a problem. On the 246 transfer case, you are developing a problem or have one with the clutch disks or plates if you can turn the shaft easily by hand

[2000DV4.8]

Ive been a master tech for 15 years, worked at gm dealer 8 years and now firestone. I have rebuilt many 246 transfer cases. Your front drive shaft with the 246 will always turn. You probally won't even be able to turn it by hand.

 

 

I can turn mine easily by hand. Very easily.