Masstro

Hey everyone, sorry for the long post, I have some background info.

Don't laugh, but im trying to wire up a system in my 2000 Astro LT AWD that will let me have "selectable" AWD, meaning I can run 2wd, locked 4wd, and auto AWD(how it runs stock).

The way the AWD system works in the Astro is that it has an auto transfer case which can vary torque distribution between 0:100 and 50:50. It varies the torque based on info received from the wheel sensors front and back so when it sense slip it sends power forward.

What I would like to do is take the 4wd selector switches out of a 2000 or so suburban and put it in the van where "Auto 4wd" makes it work as is, "2wd" forces it to stay in 2wd and 4hi/lo forces a 50:50 split.

I was hoping someone here could help me out in finding the pin configuration on the switch. Here is a picture of what i am talking about.


At this point im just thinking, I know that this will be a pain even if the switch works the way i hope it does(not all computer communication. An help is much appreciated.

Thanks,
Masstro

vester

I think the switch you have is probably all computer communication on the GMLAN or whichever data bus GM used in that era.

From what I can tell, you want to use the switch to provide 3 discreet outputs. 2HI, 4HI and Auto and then use these inputs to trick the transfer case into doing what you want it to do.

You could open up the switch and tap directly into the micro-switches behind the plastic covers and then wire that into a relay box that will only allow one button to be active at a time. i.e. when you press Auto from 2HI, it turns off 2HI and latches Auto. You also need to make sure it will retain the last selected position after a powercycle. Although it will not look as clean, I would suggest using a three position toggle or rotary switch. Something like this.

How are you planning on controlling the transfer case? Are you going to attempt to directly shift the encoder motor? You may also have luck taking advantage of the fault situations in the 4WD system. I know for certain faults in my transfer case, it will revert to 2HI or 4HI depending on the nature of the fault. There is a TSB describing the operation for my transfer case (06-04-21-006A), but it does not mention yours. You could use the switch to induce a fault that would generate the driveline position you are looking for.

vester

I was going to tell you to check out astrosafari.com, but it looks like you already found them! Those people know their stuff when it comes to these vans.

http://www.astrosafari.com/viewtopic.php?f=70&t=6520

Masstro

Yea that forum has so much knowledge on it, its great. I know that it is possible to make an 2wd/awd switch, some people there have done it. I was hoping to use the switch out of the suburban so that it would look awesome and OEM.

I was afraid that the switch would be a link to the computer, and not a direct connection to the Trans Case. So basically it would be a major pain in the but to get it to work.

Im pretty sure the transfer case torque distribution is based on an input signal from the ECU(varies voltage or something). Anyways i was hoping to have it so that the switch would bypass the ECU signal, and send a constant pre-specified voltage in 2wd/locked awd, and then use the ECU signal in Auto 4wd so it functions as if stock.

Ill probably just use two normal switches to control it if it is as much of a pain as it appears.

Thanks for the info.

PS. Does anyone know if the older suburban/silverado switches were mechanical push button, as opposed to just a button which communicates with the ECU?