problems with a np149 transfer case can i swap for another transfer ca

Androo Thelen · April 22, 2015

hi guys, im new to the forum

let me start by saying i know very little about vehicles- however i will be having my father in law read all the posts with me as he is one hell of a mechanic.

that being said i have a 2001 GMC Yukon Denali XL and i love it. except for the fact that once ive been on the road for awhile or go out of town when i try to turn there is a very bad grinding/rubbing sound- seems like the front tires are jumping around

after researching and trying different things (things that we did are listed below), we think it is coming from the transfer case not unlocking the 4x4. To be more specific we think it is the VISCOUS COUPLING inside the transfer case gone bad.

we are thinking of rebuilding the transfer case (just the cost of parts and new viscous coupling) or we were wondering if it would be better to swap it out for a completely different *yet compatible* transfer case. is there anything that would be compatible or would you guys recommend anything?

Any and all help is greatly appreciated!

THINGS TRIED:

changing all fluids in transfer case

additives in the transfer case (and without)

we did the viscous coupling test where you take the front drive shaft off and try to rotate the cylinder- we couldn't rotate it, it barely moved with all our strength

when the front drive shaft was out (and it being two wheel drive all the time) the problem completely went away, i told him just to leave it like that but he said somewhere on line that it was bad for the transfer case- is it really that harmful?

Chris · April 22, 2015

No other transfer case is compatible to swap with a 149. And the AWD never unlocks. It is full time. That is why it has a 149, the Sierra Denali and Silverado SS also used the same transfer case

desrtrat · April 22, 2015

hi guys, im new to the forum

let me start by saying i know very little about vehicles- however i will be having my father in law read all the posts with me as he is one hell of a mechanic.

that being said i have a 2001 GMC Yukon Denali XL and i love it. except for the fact that once ive been on the road for awhile or go out of town when i try to turn there is a very bad grinding/rubbing sound- seems like the front tires are jumping around

after researching and trying different things (things that we did are listed below), we think it is coming from the transfer case not unlocking the 4x4. To be more specific we think it is the VISCOUS COUPLING inside the transfer case gone bad.

we are thinking of rebuilding the transfer case (just the cost of parts and new viscous coupling) or we were wondering if it would be better to swap it out for a completely different *yet compatible* transfer case. is there anything that would be compatible or would you guys recommend anything?

Any and all help is greatly appreciated!

THINGS TRIED:

changing all fluids in transfer case

additives in the transfer case (and without)

we did the viscous coupling test where you take the front drive shaft off and try to rotate the cylinder- we couldn't rotate it, it barely moved with all our strength

when the front drive shaft was out (and it being two wheel drive all the time) the problem completely went away, i told him just to leave it like that but he said somewhere on line that it was bad for the transfer case- is it really that harmful?

NVG 149 Transfer Case Description and Operation

The RPO NP3 is a single speed, single mode transfer case. The mode is full-time all wheel drive. It has a planetary differential gear set that splits the torque, normally 38 percent to the front wheels and 62 percent to the rear wheels.

The NVG 149 utilizes magnesium housings. Proper fasteners, brackets, and fill/drain plugs must be used to prevent galvanic corrosion. The planetary differential uses the carrier (6) as the input. The annulus gear (4) connects to the rear output shaft (5) and rear wheels. The sun gear (3) connects to the front output shaft (7) and front wheels through the chain (8) and sprockets. The viscous coupling (2) consists of a sealed housing filled with a high viscosity silicone fluid and thin steel plates alternately splined to the inner and outer drum. The inner drum is connected to the input shaft (1), and the outer drum to the sun gear (3). Whenever there is a speed difference between the front and rear wheels, the inner and outer plates of the viscous coupling spin relative to each other and the silicone fluid provides resistance. The resistance was tuned to be high enough to bias power quickly to the wheels with traction, and low enough to prevent binding in a tight turn on dry surfaces. This is the most common way the viscous coupling is activated, the shear mode. If the speed difference is high, the coupling can lock or hump. This "hump" occurs when the heat generated, expands the fluid inside the housing, changing the fluid dynamics between the plates. This results in pressure between the plates, forcing them into contact with each other, similar to a clutch pack. In the hump mode, the coupling can bias torque 100 percent to one axle, if required. Situations requiring this are extreme such as backing up a steep gravel grade or climbing over off-road obstacles. The viscous coupling is not serviceable; it must be replaced if defective. This is because each viscous coupling is calibrated for optimum vehicle performance for both the shear and hump modes. If the viscous coupling is in the "hump" mode too long, severe damage will occur. To prevent damage to the viscous coupling, DO NOT:

Tow with only two wheels down

Drive without one propshaft

Drive with a "donut" spare tire for an extended period of time

Power Flow - No Wheels Slip

During normal operation, 100 percent torque is delivered to the input shaft (1) from the transmission. The torque is split to 62 percent to the rear output shaft (2) and 38 percent to the front output shaft (3), by the planetary differential. Because there is not a loss in traction or slip in the front or rear wheels, the viscous coupling is locked in place and there is no "shear" mode or "hump" mode involved.

Power Flow - Front Wheels Slip

When traction is lost at the front wheels, the viscous coupling works in conjunction with the differential to bias the torque more to the rear wheels. The rear torque goes higher than the 62 percent, and up to 100 percent torque to the rear output shaft (2). The torque at the front output shaft (3) is lowered from the 38 percent, to as low as 0 percent torque.

Power Flow - Rear Wheels Slip

When traction is lost at the rear wheels, the torque is biased to the front wheels. The torque to the front output shaft (3) goes higher from the 38 percent, up to 100 percent torque. The torque at the rear output shaft (2) is lowered from the 62 percent, to as low as 0 percent torque.

Customers may have concern that the transfer case is not operating properly because one set of tires spun for a brief period. It is normal for one set of tires to spin until the viscous coupling engages.

Turning off the traction control switch, if equipped, enhances the function of the viscous coupling. The viscous coupling, as described above, engages by heat. Allowing one set of tires to spin or slip for a brief period will generate heat in the viscous coupling. The engine speed should be kept at a constant speed during the brief spin of the tires. Pulsating the engine speed or hard acceleration will not allow the viscous coupling to operate properly.

Document ID # 873908

2003 Chevrolet/Geo Chevy K Silverado - 4WD

******************

Transfer Case Viscous Coupling Test

Tools Required

J 45382 Transfer Case Tester

To determine if the viscous coupling is operating correctly, use the following test procedure. Testing the viscous coupling operation by removing a propeller shaft and driving the vehicle will cause the viscous coupling to fail. The test will determine if the viscous coupling is faulty from a totally locked up failure, or if the viscous coupling fluid has leaked out from being severely humped.

Important

The Viscous Coupling Test is very sensitive to the temperature of the transfer case. If the transfer case is very hot, the time to turn will be faster. If the transfer case is cold, the time to turn will be slower.

1. Operate the vehicle for 24 km (15 mi), or until normal operating temperatures are reached.

2. Set the parking brakes for the rear wheels.

3. Position the transmission in NEUTRAL.

4. Raise the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.

5. Remove the front propeller shaft. Refer to Propeller Shaft Replacement - Front in Propeller Shaft.

6. Install the J 45382 into the transfer case front output shaft.

7. Using a torque wrench at 11 N·m (100 lb in) on the J 45382 , turn the front output shaft 90 degrees.

8. Note the length of time it takes to turn the front output shaft the 90 degrees.

* If the front output shaft turns slow, and takes at least 10 seconds, the viscous coupling is operating correctly.

* If the front output shaft will not turn, the viscous coupling or the planetary carrier assembly could be locked-up.

* If the front output shaft turns easily, and the 11 N·m (100 lb in) cannot be obtained, the viscous coupling is faulty.

Androo Thelen · April 22, 2015

Ok so no swaps are possible. Sorry Chris but I thought i understood that this transfer case is not 4 wheel drive all the time and automatically switches back and forth based on the viscous coupling inside. Apparently I'm wrong?

It drives fine when u start but once you gain speed and slow back down and turn the front tires hop and skip.

We tried the viscous coupling test that says your supposed to be able to rotate it with 100ftlbs. It Didn't budge. (But apparently it's not supposed to? )

Thanks guys. So far it seems like my options are to either rebuild my current or get a different 149 tran case.

Anybody have any info or tutorials on rebuilding one, I've found diagrams but nothing else really. My father in law thinks if he gets some service info he could pry do it.

Androo Thelen · April 23, 2015

Unless I'm completely looking into this too much. Is there hubs or tie rods or anything else besides the transfer case that could be causing this . I just want to make sure I have all my things checked before spending 1500$ on a new transfer case

Chris · April 23, 2015

The viscous coupling is just a torque vectoring device. One of the axles may have issue. I have read quite a bit about the 149, i dont know much about the front axle used in those. It could also be rear axle as well. Please dont just throw parts at it. That can get expensive quick. Take it to a reputable shop. The $100 diagnostic fee can go a long way.

Androo Thelen · April 23, 2015

Lol Ok I've never had to go to a shop for anything so I don't know how all that works. I hear mechanics shop and I immediately see $$$$ .my father in law has always been able to fix things luckily. But on this one he's stumped. like I said I thought I did research but maybe I got an idea stuck in my head and kept reading

Is there anything I can test or look at myself (I have a mechanic willing to try anything but just doesn't know where to start) I'd hate to go waste 100$ or whatever it costs for the mechanics in this town (small town and theres not very many) to misdiagnose and waste my time and money

Chris · April 23, 2015

Lol Ok I've never had to go to a shop for anything so I don't know how all that works. I hear mechanics shop and I immediately see $$$$ .my father in law has always been able to fix things luckily. But on this one he's stumped. like I said I thought I did research but maybe I got an idea stuck in my head and kept reading

Is there anything I can test or look at myself (I have a mechanic willing to try anything but just doesn't know where to start) I'd hate to go waste 100$ or whatever it costs for the mechanics in this town (small town and theres not very many) to misdiagnose and waste my time and money

The $100 i said is usually what a dealer costs to look at it. I do most myself and the times i visit shops are for dealer programming or alignments whi h is where my truck is sitting now