Transfer case unit or just the transfer case shifting motor?

[doug383]

Hi all,
I'm new here so I will try to be brief. I have a 2005 Trail blazer LT with a straight 6, all stock no mods. A few months after I bought it the 4WD light started coming on and going off. During a snow storm my wife put it in A4WD, it ended up getting stuck in 4WD HI. It released when restarted. A week or two later It did it to me (ruling out that she didn't put it in neutral before making the shift). We left it out of A4WD and just used 2WD for the rest of the winter. Last week I pulled up to a traffic light, when it turned green the engine just revved like I was in neutral. I tried to put it in park and it would grind like my teenager trying to drive a stick. I shifted to neutral and restarted pointlessly. So I tried A4WD, to my pleasant surprise I was able to drive it home this way.
I do know Cars quite well but not 4WD's. I am lead to think it is an issue in the transfer case. I have read a lot of post's by Roadie and am lead to believe one of the following:

Transfer case shift motor and or aliment
Shifting linkage inside the transfer case and or aliment
The undersized bearing Roadie has mentioned in past posts

Any help and or thought will be greatly appreciated
--383

 

[Wooluf1952]

You only have to put the trans in neutral when going in to, or out of, 4LOW.

 

[IllogicTC]

The "neutral effect" along with grinding into Park is usually a symptom of a blown input in the transfer case, generally the planetary gearset. But with your description of things going a bit goofy previously with the 4x4, I would lean toward transfer case encoder motor. If the 2HI position is considered the center (imagine like a steering wheel lined up to go perfectly straight down the road), it either turns clockwise to begin applying pressure to the clutch (and eventually lock the clutch fully in 4HI), or turn counter-clockwise from the center to flip the transfer case into it's neutral zone which is the area between the high- and low-speed gear sets.

So, turning to A4WD may have made the encoder bring the high-speed teeth back into engagement (when expected to be in 2HI, it may have drifted toward the 4LO area somehow). I would inspect wiring and do testing of the encoder motor. I can't recall exactly what the resistance should be in an expected position, it may either be reporting wrong, going plain haywire, or something else. The Roadie will likely drop by here and lead you further to the Promised Land of DIY Success.

For future reference, if you experience this any more while attempting to troubleshoot or fix, first set the transmission to Neutral and allow the transmission a bit of time to spin down. Then shift briskly (not crazy quick, but don't hover in Reverse either where the trans will spin back up) into Park to engage the pawl. If the TC is still in neutral though the pawl will do nothing, so it is also suggested to use your parking brake.

 

[The_Roadie]

I'm thinking encoder motor as well, specifically the brake. But let's back up a bit first. How many miles, and what's your maintenance history? How many miles since your last fluid change on the tranny, differentials (both) and transfer case?

When you had the issue when you were driving home in A4WD (a mode to avoid using ever), is there a chance you were being pulled home by the front wheels and the rear was not driven?

Have you read my descriptions of the two noises you should hear in the various 4WD mode transitions? You can do them in your driveway with the ignition on and the motor off to hear them better. What is its behavior today, in the motor noises you hear for each of the mode transitions, AND the appearance of the mode switch lights?

 

[doug383]

Thanks for the response guys,
To answer Roadie's questions, Yes I avoid A4wd. The Trailblazer is just shy of 80K miles. As for maintenance It has had all scheduled on time since I have owned it (right at one year). It was done as part as the maintenance package from the dealer (not a Chevy dealer). So I am going to suspect the differentials and tc fluids have never been changed. I am planning on doing them when I tear in to the thing.

When I drove it home it felt like the rear wheels where doing the work. but I cant be positive I wasn't be pulled by the front. On the auto selector for the 4WD the lights seam to be functioning correctly. It flashes to the selected position you can hear the motor shifting position, then the light goes on solid when the shift is complete. I was not listening for two distinct different sounds on that though (can you by chance lead me to the thread were you described them)? I will pay more attention to it tonight.

The issue still remains the same, it will lock in to all 4WD functions. 2WD is just gone. When in 2WD after shifting from park to any gear and trying to go back in park it grinds. Waiting and quick shifting back to park does not help, I have to shut the engine off or go back in 4WD.

I would imagine if it were to be a blown input or planet gear I would either lose all drive or get horrific sounds from it. Correct?

You both mentioned the encoder motor. Just to verify I am thinking the correct part, is this it?

 

[The_Roadie]

That's the encoder motor all right. Quickly, the two noises are:

1) The front axle actuator is a high pitched whine that takes almost one second, and it ONLY makes a noise in the 2HI->A4WD and A4WD->2HI transitions.

2) The encoder motor is a lower pitched noise that takes under a second, and it sounds off in EVERY possible mode transition.

To listen to these, move the mode switch only one step at a time. Like don't jump from 2HI to 4HI directly.

If the "free" maintenance didn't include the mandatory 50K transfer case fluid change, they cheated you and could perhaps be held responsible for any internal TC damage if you find any. Read your contract.

 

[doug383]

When I bought it, it was well over 50K. I doubt it is in there.

 

[doug383]

K so update... The encoder motor is defiantly all jacked up! Hey it's cheaper then replacing the entire transfer case.

Roadie thanks so much for explaining the two sounds. Soon as I new what I was listening for it was a night and day difference.

So today it would not engage 4LO. You could hear it try but no go. It would engage 2WD temporarily before falling out, BTW sounded horrific.

I am ordering the part tonight and will update. Soon enough I am going to need to find something else to hold my drive way down...

Thank you all so much.

Thank you all so much!

 

[doug383]

So my part came in!
I am going to change the Diff fluids as well as the tc fluid when I crawl under this thing. What are the best fluids to use?

 

[The_Roadie]

The ones called for in the Owner's manual.

And discussed in a few threads on the site.

Mobil 1 75-90 LS synthetic gear oil for the diffs.
GM (only) Auto Trak II transfer case fluid.

 

[doug383]

New encoder motor is in and works like a charm.

Thanks all.