Chevy & GMC Vans

As much as I would love to install the 4WD transfer case, that may be more effort than I really need to take on right now.
Is it possible to install a 3-way switch to either defeat the AWD for mileage, engage the AWD for low-speed, low-throttle crawling or just left standard?

Just thinkin' out loud...

I don't remember the yr exactly maybe 97 or 98 and on you could add a switch to disengage the AWD. A couple of the members have done it and I know there are a couple threads about how to wire up the switch around here somewhere.

1999 was the first year for the computer controlled transfer case. There have been a couple on vans modified to turn the AWD off with a switch. It does seem plausible to set it up with a 3 way switch that would effectively add a 4HI mode. Just remember to turn it off on pavement.

Yep, I installed an AWD disengage switch. Basically, just wire in a switch in place of the ATC fuse under the hood. I added an in-line fuse also so that it was still properly fused to be safe. Really simple to do and it actually gave me about 2 mpg.

Thanks guys! I knew about the defeat part, and was planning on doing that this weekend, but was wondering about the locked engage for crawling around loose, steep scree in the mountains. Figured I do both at the same time...
After some more archive searching I found the thread where it appears there is no way to manually engage the system.

LiftedAWDAstro said this: "There has been no solution to electronically locking the 99 and newer NP136 transfer cases."

Mine is a 2000.

Until I find out differently, I'll go w/ that.

ihatemybike wrote:1999 was the first year for the computer controlled transfer case. There have been a couple on vans modified to turn the AWD off with a switch. It does seem plausible to set it up with a 3 way switch that would effectively add a 4HI mode. Just remember to turn it off on pavement.

The "engage motor" or whatever it is called is opperated by a PWM signal, and would be hard to replicate to act as 4HI. It would just burn out the motor (actually kind of a solonoid) fairly quickly to put 12+ to it with a switch.
It is possible, I'm sure, but not easy. The 236 T-case uses an engage solonoid that locks somehow, maybe it could be adapted.

BTW, I have a NP231, both driveshafts and a shifter I'll be selling for a 4x4 astro swap from my '91. I'm going to run a NP241 in my new 4x4, so I doubt the shafts will work. Maybe I should check that before a "speak" too soon, lol.

Where on a 95 is the ATC fuse located?
Thanx,
Don

I think on a 95, you can't turn the awd off. I'm not sure but I know that the switch thing only works on the newer units.

Logan is correct. The 95 t-case is 100% mechanical and can not be "turned off".

this is probably a stupid question, but could you add an s-10 front diff with a locker with that switch?

New member - greetings all and thanks in advance ;-)

I have a 1998 awd astro and wondering when the 99 electrical awd tweakability came into effect.
Can anyone offer any detail on dates, or some method to confirm/deny my 98 didn't squeak into this category?
Wishful thinking I admit, but 2mpg is 2mpg.

cheers

tandrews wrote:New member - greetings all and thanks in advance ;-)

I have a 1998 awd astro and wondering when the 99 electrical awd tweakability came into effect.
Can anyone offer any detail on dates, or some method to confirm/deny my 98 didn't squeak into this category?
Wishful thinking I admit, but 2mpg is 2mpg.

cheers

The '90-'98 AWD vans use the BW4472, a mechanical (viscious coupling) transfer case. No adjustments, electrical hookups, etc.

The 1999-2005 AWD vans use the NV136 that uses a PWM solonoid to activate a wet clutch that engages the front driveshaft.

There are a few good explanations of how the systems work here on the site, if I come across them, I'll reply with some links.

So what bad could come from just pulling the ATC fuse and driving in 2-wheel, specifically towing.

Not sure why you would want to do that. My AWD never engages by itself unless I'm off-road or on snow, in which case it's a very good thing.

Well, as Logan said earlier in the thread he gained 2 mpg... If it's as easy as popping the hood and pulling a fuse to gain 2 mpg during dry summer months, why not?