Four wheel drive

Motodox · June 1, 2015

Ok so I was having four wheel drive issues and swapped out transfer cases over the weekend. I believe we are all good now. It locks in now and you can feel the tires grab on pavement when turning. Which to me is great my 4wd definatly works.

My question is does the transfer case always have the front drive shaft locked in on the transfer case even in 2wd? Because mine is. Even in 2wd I can't spin the front drive shaft by hand when stopped in park. So is it only your front diff that locks in and out? I was curious if this tcase I just put in was performing as it should.

CapitalTruck · June 1, 2015

I just went out to the street and checked mine, with the vehicle in park and the transfer case in 2wd the front shaft can be spun by hand. Something is still going wrong there. I almost didn't even want to tell you that. I should add that I have the manually engaging transfer case, however, I don't think that should make a difference.

kstruckcountry · June 1, 2015

It's not right.

BlackZ71Silverado · June 1, 2015

With the Autotrac transfer case, the front drive shaft should spin all the time. While parked and in 2wd. It may not be really easy to spin without a good grip on the sucker. It can take about 35-40lbs to spin it by hand.

You definitely have an issue if it feels engaged and the shaft will not spin freely.

Are you sure the truck actually disengages from 4x4 when you press the button? With the shaft not spinning it seems as if the shift module isn't working.

It's difficult to diagnose these issues on the internet. I would suggest you take the truck to a different shop and have the job done properly. Whoever did the rebuild and installed that t-case for you has an issue somewhere and they should pay to have it corrected.

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Motodox · June 1, 2015

Thank you for the great reply, I actually did all the work myself. I just pulled the tranny had it built then reinstalled it and tranny is perfect now. But my tcase I knew wasn't working correctly so I swapped it out for another used tcase that supposed to be good.

My indicator shows its in 2wd but yet I can not spin the drive shaft by hand. I know the front actuator is disengage because I can feel the wheels not grab on drive pavement. When I switch to 4wd the indicator blinks then stays on 4wd and I can feel the front wheels are very grabby almost hard to turn on pavement. I'm just worried the t case isn't coming out of 4wd. I didn't know if the front shaft was supposed to disengage or not. Apparently mine doesn't and it only disengages at the front diff.

Let me ask, is this ok if I leave it? I don't see why just having the front shaft being locked in and front diff unlocked it would cause any issues.

My tcase before I would switch into 4wd it would clunk and the light would stay on 4wd but I could reach down and spin the shaft separately from the rear shaft. That's when I knew something was bad.

Motodox · June 1, 2015

And to answer your question black71 when I put the truck back in 2wd at the switch the light blinks then stays on 2wd like it did disengage from 4wd.

BlackZ71Silverado · June 1, 2015

Do you have the Autotrac transfer case? If you do, you will have the 4x4 Auto option at your 4x4 switch.

Motodox · June 2, 2015

Blackz71. Yes it is the autotrac. It has the auto 4wd and 4wd is switched from the dash push button. I even used the blue fluid in the tcase when I switched it out to the new used tcase. Believe the fluid is called auto trak II

Motodox · June 2, 2015

In 2wd the front diff unlocks but the front driveshaft stays locked into the transfer case cause I'll reach down and try to spin it by hand and it moves the rear drive shaft. So I know it's staying locked in.

With the diff unlocking properly is this anything to worry about? The wheels arnt locked in to the front shaft. Is there anything I should worry about with the front shaft staying locked in to the tcase or is that how it is with the auto Trac tcases

BlackZ71Silverado · June 2, 2015

In 2wd the front diff unlocks but the front driveshaft stays locked into the transfer case cause I'll reach down and try to spin it by hand and it moves the rear drive shaft. So I know it's staying locked in.

With the diff unlocking properly is this anything to worry about? The wheels arnt locked in to the front shaft. Is there anything I should worry about with the front shaft staying locked in to the tcase or is that how it is with the auto Trac tcases

We actually just replaced a GM transfer case at the shop. Sounds like you are going to be ok, that's how the AutoTrac works. The front driveshaft stays locked into the transfer case and allows the front drive shaft to spin freely, nothing to worry about there.

Here is some information from the shop about the AutoTrac Trasnfer Case from GM. This was released when GM started using the new autotrac transfer case a few years ago. It may help you better understand what's going on and how it works.

The New Venture Gear model NVG 246 RPO NP8 transfer case is a 2-speed automatic, active, transfer case. 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 0-6.78 N•m (0-5 lb ft) 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.

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 3 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

Motodox · June 3, 2015

Blackz71silverado. Thank you so much!

That's great news! That is the best answer I've ever received to any question asked on a forum thank you again for your time and helpfulness. It's much appreciated!

Take care!

CapitalTruck · June 4, 2015

I just have trouble believing that front propeller shaft should stay locked in when the transfer case is in 2wd. I'd I go out to the street now I can turn the front prop shaft by hand, this is with the truck in park with the parking brake set.

BlackZ71Silverado · June 4, 2015

I just have trouble believing that front propeller shaft should stay locked in when the transfer case is in 2wd. I'd I go out to the street now I can turn the front prop shaft by hand, this is with the truck in park with the parking brake set.

Should not be hard to believe at all, that's how it works. Been that was for a long time now.

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Motodox · June 4, 2015

I just have trouble believing that front propeller shaft should stay locked in when the transfer case is in 2wd. I'd I go out to the street now I can turn the front prop shaft by hand, this is with the truck in park with the parking brake set.

Do you have a manual shift transfer case ? Maybe the front shaft only stays locked in on the autotrac 4wd the tcases with push button and auto 4wd.

At this point I hope the autotrac tcases are supposed to stay locked just from front shaft to tcase, that would mean my tcase works correctly !!! ?

00Silverado4x4 · June 4, 2015

I apologize but I have to disagree. Both on my last and current truck the front drive shaft did/does not stay locked in while in 2wd. When I replaced the engine oil cooler lines I ended up dropping the front U-joint down to give me extra clearance. I would put the truck in 4wd to lock the shaft so I could loosen the bolts and then 2wd to spin the shaft around.

My question is did you double check that everything was plugged back in when you reinstalled the transfer case? Maybe the shift motor isn't getting power or signal to shift as it should be.