First off, I have searched everywhere on a ton of different forums and haven't found anybody that is describing the issue that I'm having. The issue: Just bought a 1997 T100 4x4, and the 4x4 doesn't engage. What happens when I shift into 4hi or 4lo: Light on the dashboard immediately lights up, I hear a clicking in the dash from the relay, and I hear a sort of wirring/rubbing sound coming from the tcase/diff area. I have checked all the vacuum lines, solenoids, etc. Vacuum is applied to the right lines at the right time, so I have ruled out the solenoids and possible vacuum issues.
With the front wheels jacked up in 2wd, both wheels spin freely (not moving the others, like a 2wd truck.) When I shift into 4wd, the wheels slightly turn each other but they are not locked in like they should be. I thought the ADD in these trucks kept the front axle locked, even in 2wd. But obviously I'm misinformed. Plz halp.

 

Have your tried 4wd in any situation other than on a jacked up truck? Stock 4wd is going to be a part time 4wd system with OPEN differentials - meaning that both opposing wheels are not tied in/locked to one another. With all wheels having traction the 4wd works great, but if you lift a tire, that's the one which will get power. Seems dumb, but it has mostly to do with on-road driving behaviors and turning while locked in, etc. most regular people who need automatic trans and don't know how to drive definitely wouldn't be able to handle real 4x4 on the road in the snow.

So to answer, it sounds normal to me. The whirring sound is likely your tcase when in 4wd, mine does it. When jacked up you should definitely observe the front driveline spinning.

 

Yes I have tried it, and it doesn't work. This isn't my first 4x4, I had an 88 yota 4x4, an 88 Montero, etc. Mostly 5 speeds. So I know what a proper, unrefined 4wd system feels like

What confuses me is that the 4x4 light comes on, and I thought that was the last link in the chain of commands, but something down the line is not connecting. I just got back inside from removing the actuator on the front diff. It is indeed working properly, not frozen up or even stiff. Put it all back together and of course, I'm still without 4wd. Is there an actuator on the transfer case that engages the front driveshaft? It's really cold in Minnesnowta right now so I'm trying to minimize the time spent outside.

 

Then sounds like your problem is there at the tcase. Does front driveline not engage?

 

I don't know the T100 but I have on a Nissan and a Ford had to in the past get under the truck to manually lock and unlock the transfer case and worked on it on warmer days at a later time. Not sure if that is possible on yours.

 

UPDATE: Jacked all 4 off the ground, front driveshaft is shining but not the front wheels. Is it possible that the splines that the sleeve slides over are sheared off? I'm clueless at this point. Anybody??

 

You're sure the ADD actuator is working properly? IIRC you can see the splines on the coupler sleeve if you had it open before. My guess is the arm isn't sliding the sleeve all the way over/not working properly. If you manually move the actuator over and lock in the sleeve, you should be getting the front wheels moving. That would confirm the add isn't working.

 

Yes I am sure the actuator is working, I took it off while it the truck was running and all wheels jacked up, slid the sleeve over every position possible, same thing- no front wheel motion. The splines that the sleeve slides over look good, everything looks clean and in working condition. Is there a clutch pack inside the diff? My next move is to disassemble the front diff and see whats up inside there I guess. Sigh...

 

If the sleeve is actually engaging then it must be internal because that's all that is left really. The axles are tied in to diff with flanges at the wheels. At a minimum you should get passenger wheel to move since it's got a solid axle shaft to the carrier inside unlike the long side which is split and gets tied together by the sleeve. When you spin the front passenger tire do you hear metal crunching inside the diff?

 

did you drain the oil out of the differential yet and check for metal?

so since the title says "guaranteed or money back"
I would take the truck back

 

It doesn't look good. Drained the fluid, the plug had a grape sized chunk of metal shavings clinging to it, and the oil was full of metal specks. The diff obviously has something screwed up inside it. Have one stubborn bolt on the rear of the diff I'm battling, then I will have it down and apart.

 

yup, take it and get your money back.