Diagnosing 4wd Confusion...thought it was solved...its not:(

[Mudwheelin]

So a few minutes ago I tried to self diagnose the 4WD system. I followed the "how to" to a tee. So I lifted the Passenger tire off the ground. Will it rotate? Yes it does. Watch the front prop shaft. Does it rotate? Yes it does. So that should mean that there is a problem with TC. But for the heck of it...I lifted both tires off the ground. I rotated the the front passenger tire. Does the driver tire rotate? No it didnt....So the problem should be with the 4wd Disconnect.

So now im confused. Which is it? The 4wd disconnect or the Transfer Case?

If this helps:
2007 Trailblazer LS
110,000 Canadian KMS.
All fluids are up to date.
2.5" Markmc Suspension lift
2" Markmc body lift.

Thank you in advance for the help. Hopefully the wife doesnt kill me. Were getting married on the 19th this month and I would like to drive the TB to the wedding. But the roads are so icy here, so I need the 4wd working. Thanks guys!

[The Roadie]

Need a couple more details. You were in 4HI mode, not A4WD? When both front wheels were off the ground, the driveshaft was NOT turning?

You could have a problem with BOTH elements. I'd troubleshoot the splined disconnect first.

Edit: When was the last time the system worked? How current are you on transfer case fluid changes?

[Mudwheelin]

I had it in 4HI mode. Thats what the how to says to be in. The last time I used 4wd was right before the body lift. So about a month ago. Sadly...Im alittle over on changing the front fluid. When both wheels were in the air the drive shaft was turning.

[The Roadie]

When both front tires were in the air, did you try to turn the driver's side wheel? It might be that the differential has a bit more friction than normal, and then then the driveshaft turns because the transfer case clutches are dead. With your current symptoms, I'd now suspect the transfer case first, but the differential has entered as a suspect. Or the wheel hub could have high friction if it's dying.

Try putting it into 4LO mode, both front wheels in the air, and turn each of the front wheels and see what else moves. If the drive shaft is one of the things that rotates, get somebody to halt that from rotating, and see if you can ever cause the expected behavior on the front tires where the one you're not rotating goes the OTHER way.

[Mudwheelin]

Kind of a stupid question here...Are we talking about the drive shaft under the vehicle or the shafts connecting to the wheels? If were talking about the one under the vehicle Ill have to start this process over again. Please dont be pissed at me lol.

[The Roadie]

The round things that connect the wheels to the vehicle are CV shafts. They run perpendicular to the main axis of the vehicle. The round things that go fore and aft from the transfer case to the front and rear differentials are what we call driveshafts.

The CV shafts are permanently attached to the wheels since we don't have disconnectable hubs, so the troubleshooting process doesn't even have those as a variable.

Not pissed - don't worry. We save being pissed for folks who can't recognize the differential and think the TRANSFER CASE is bolted to the side of the oil pan. They get thrown back over the fence to trailvoy.

[Mudwheelin]

LOL, I had I feeling I did it wrong. Im going to go and check it out right now. Ill do the test properly this time. Sorry about that.

[Mudwheelin]

Ok this time I did it right. Put it in 4Hi. Will it rotate? Yes it does. Does the drive shaft rotate? No it doesnt. Lift both tires. Does the driver tire rotate? No it doesnt. So im guessing that means the 4wd disconnect is bad? I can hear abit of grinding in there if that make a difference. It also feels abit wobbly. The thing that weirds me out, is that the light for 4wd drive is on. It doesnt blink. The light stays solid. What would your expert opinion be for my problem being with the 4wd disconnect?

[Trail X]

Mechanical disconnect failure. Only way to know is to tear it apart and rebuild.

[Mudwheelin]

Ya thats what im going to do. I noticed while searching the forums that roadie had said something about a company thats going to provide rebuild kits for us. Has that been done yet? If not should I order all the parts listed in your how to, except for the housing? Thanks for the help guys.

[The Roadie]

... a company thats going to provide rebuild kits for us. Has that been done yet?...

Dorman was the company, and they failed to bring it to market yet. Disappointing. But in the meantime, another company stepped up and offers them. A few victims of the AAM misdesign have bought them./ No word yet on long-term reliability, but many junkyards have become aware of the failure rate and jacked up their prices accordingly. There are probably no more $50 disconnect assemblies left out there.

Aftermarket vendor: "ATP 111001 Front Axle Disconnect" available on Amazon for just under $300. Advanced Auto Parts for $556. Others in the middle.

... The thing that weirds me out, is that the light for 4wd drive is on. It doesnt blink. The light stays solid. What would your expert opinion be for my problem being with the 4wd disconnect?

It's the disconnect. Mechanical failures inside the disconnect or the transfer case won't show up as a blinking light or a "Service 4WD" lamp because the designers didn't design that feature in. They designed position feedback sensors into both the front axle actuator and the transfer case encoder motor, but probably due to excess cost, didn't extend the sensors to actually determine the functionality of the 4WD system. That would have required an interface between the wheel speed sensors (part of the ABS system designed by somebody other than AAM - American Axle & Manufacturing) and the TCCM. Cooperation between systems designed by different companies isn't likely to happen unless GM documented a spec and forced them to talk. Since the system was designed to last just long enough to get out of warranty, and post-warranty lifetime is only a moneymaker for GM and the dealer network, they had no incentive to invest even a nickle in a better system.

To be precise, a FEW failures can show up as a blinking mode switch light, but only if the fault also jams the actuator or encoder motor to the point it can't complete its commanded movement. More rare, but possible.

[Mudwheelin]

Aftermarket vendor: "ATP 111001 Front Axle Disconnect" available on Amazon for just under $300. Advanced Auto Parts for $556.

Ok so just to get this straight. The ATP 111001 from Amazon is a rebuild kit? Would it be less expensive to buy the parts seperately? Thank you for all the help.

[Trail X]

Not a rebuild. That's an aftermarket supplier that offers a replacement product.

[Mudwheelin]

Lol, just figured that out actually. Would it be easier to buy the parts seperately? Im assuming it would be less expensive?

[The Roadie]

If you take yours apart and figure out exactly what needs replacing and then get JUST those parts from parts4chevys.com and they are available, and they add up to less then $300, then by all means get just the parts. If you don't have a broken housing, it may be cheaper. Nobody can advise until you see what's broken, and at that point you won't need our advice. Just do the math. If ALL your internal parts are bad including the bearings because of metal migration, it may be less expensive to get the assembly.

[Mudwheelin]

Hmm. Makes sense to just get the assembly and have left over parts from the old one. It would suck taking it all apart to see what I need, then putting it back on and taking it off a week later. How long do you think it would take to change it out? Providing I have everything needed to take it off and dont run into problems?

[The Roadie]

How long do you think it would take to change it out?

If you're a good wrench, 90 minutes. If you're light on experience or luck, 4-8 hours.

Providing I have everything needed to take it off and dont run into problems?

There is such a fantasy universe?

[Mudwheelin]

Haha. Well im thinking ill have it done in 3ish hours. Thats without problems. When I did my suspension lift I ran into so many problems...nuts and bolts not coming loose. I thought that was weird being that its only an 07. I took a look under the TB today. Everything looks nice and clean and hopefully shouldnt cause to many problems. Ill start the soaking process tomorrow.

[navigator]

I think you mentioned one of the major advantages of buying the aftermarket is you have the parts in hand to do the swap and can do it same day instead of tearing it down and then ordering the parts and waiting and being without a car for that much time.

For someone that it isn't the DD it might be ok to tear it down first.

[Mudwheelin]

Roadie... or anyone else...I found one at a wrecker for $125. Its out of an 06 trailblazer LT. The guy didnt know if it was an Awd one or for the one I have. Or does it even matter?