Info on Original Transfer Cases for Astro/Safari AWD Models

[cd0156]

I found some info on a GM website and Figured Iwould repost here since every now and then there seems to be some confusion about the OEM AWD system and the different years...


This info is for 1999 and NEWER AWD systems with electronic AWD:

The NV136 transfer case is an automatic transfer case with two drive ranges. Shifting from rear wheel drive to four wheel drive is done automatically when the transfer case shift control module receives wheel rotating slip information from the speed sensors. The transfer case shift control module then engages the transfer case motor/encoder to position the transfer case from rear to four wheel drive. When the transfer case shift control module receives information that the wheel rotation is the same on both axles, the transfer case shift control module sends position information to the motor/encoder to put the transfer case back into rear wheel drive. The 2HI position is for normal driving with the rear wheels pushing the vehicle. The 4 wheel drive position is for driving through sand, snow, mud, gravel, or heavy rain at normal or slightly below normal speeds. The NV136 is manufactured at Syracuse New York by New Venture Gear a division of New Process Gear for General Motors.


The following info is a quote from Truck Trends, and is describing the 1998 and OLDER AWD systems with the viscous coupling setup.

Pre 99 models feature a full-time viscous-coupled transfer case that will automatically transfers torque where it's needed. The viscous coupling acts as a torque-biasing device attached to the front- and rear driveshafts in a lightweight magnesium housing mounted directly to the automatic transmission. One set of the discs turns with the front axle, the other set with the rear axle. The discs are surrounded by a high-viscosity silicone fluid that, when deformed, transfers power from the faster rotating discs (or the slipping wheels) to those rotating more slowly (the wheels with grip). A 35-65-percent front-to-rear power split is used under normal operating conditions, while up to 100 percent of the engine's torque can be transferred to the wheels with traction when needed. Road surfaces needn't be slippery for the AWD system to deliver a traction advantage. If climbing a hill or steep grade, for example, the differential will send more torque to the rear wheels to compensate for the extra weight. The AWD also accommodates for speed differences that naturally occur when a vehicle travels around a corner on dry pavement and adds superior cornering capabilities under all circumstances. The system also provides better durability than a rear-drive-only system because torque is continually shared between the front and rear axles.

[cd0156]

This may help if anyone is looking for which case to do with thier swap..


And some GM automatic transmission info just for good measure..
Rear-Wheel Drive Transmissions

4L60-E
RWD 4-speed automatic with overdrive
159-176 lbs transmission weight filled
Gear Ratios:
1st -- 3.059
2nd -- 1.625
3rd -- 1.000
4th -- 0.696
Rev -- 2.294
Max Gearbox Torque: 670 ft-lbs


4L80-E
RWD 4-speed automatic with overdrive
260 lbs transmission weight filled
Gear Ratios:
1st -- 2.482
2nd -- 1.482
3rd -- 1.000
4th -- 0.750
Rev -- 2.077
Max Gearbox Torque: 885 ft-lbs


5L40-E
RWD 5-speed automatic with overdrive
186 lbs transmission weight filled
Gear Ratios:
1st -- 3.42
2nd -- 2.21
3rd -- 1.60
4th -- 1.00
5th -- 0.75
Rev -- 3.02
Max Gearbox Torque: 494 ft-lbs

[T.Low]

Hey cd, did I miss the post with the pics of your van?