Transfer Case or Transmission Failure - T-Case Interchange Help?

threefiveleven

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Jan 12, 2018
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2007 TBSS ~140,000 miles. Well maintained, daily driver, no track time and very little abuse.

Has PCM of NC trans cooler. (Added before towing.)

Got a camper last fall and took it on about a 1500 mile roadtrip behind the TBSS in December. No problems, towed fine. This is its one and only time towing / being a workhorse. Has been running/working fine for months after the trip.

Trans was shifting fine - I'm familiar with 700r4's and 4L60's and how they fail. This one had no signs of problems at all, then completely lost all forward motion driving calmly in traffic. As if in neutral.

If you put it in gear, then try to put it back in park, it grinds as if the trans is spinning. No motion coming out of the t-case though. Infinite neutral.

Is it the t-case? And, if so, what can I snag one out of? I have a friend with a t-case out of an 05 Escalade. Will that work?
 

Mooseman

Moderator
Dec 4, 2011
25,660
Ottawa, ON
Unfortunately that document omits the TBSS.

I have a friend with a t-case out of an 05 Escalade. Will that work?

I did find this over at TBSS Owners:


The Silverado SS and the TBSS transfer cases are nothing alike, not even similar in the slightest!
I know that the TBSS TC is a NV120 and the document gives a designation to the Escalade as either a NV149 NP3 or a BW4481 (Borg Warner?). So my assumption is that the TBSS TC is exclusive to it.

We don't have many (or any) TBSS owners here. You'd probably have better luck at TBSSowners.com.
 
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budwich

Member
Jun 16, 2013
2,101
kanata
perhaps you should try pulling the shift motor and manually move the transfer to ensure you aren't in neutral... of course, if you are hearing "bad sounds" out of the transmission area then it isn't likely to help doing things at the transfer case.
 

threefiveleven

Original poster
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Jan 12, 2018
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28409
Thanks for everyone's input - I should have given a better description... the noise an auto trans makes when you're rolling and try to put it in park... that's the noise it makes if I put it in D or R then try to go back to Park, which left me wondering if the t-case is gutted and the trans may be ok.

Are you saying that the AWD t-case has a neutral? Or for that matter any shifting mechanism?
 

budwich

Member
Jun 16, 2013
2,101
kanata
sorry I was just going blindly on "transfer case" versus "transmission" on the vehicle... not being aware of the "AWD" nature of this vehicle. sorry.
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,194
Brighton, CO
Sounds like the tail shaft of the transmission, or the interconnect inside the transfer case went bad/Sheered.

The only real way to see what happened is drop the transfer case.

I would highly doubt the transmission went bad. But I was also under the impression that the SS got the 4L70 or 4L80.

Edit: Confirmed, the 4L70.
Edit#2: I would almost bet its not the transmission. The parking pawl grinding noise you hear when putting it into park confirms this. The transmission is trying. There is a disconnect inbetween the output shaft on the trans, and the transfer case.
 
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Mooseman

Moderator
Dec 4, 2011
25,660
Ottawa, ON
The SS has a full-time AWD TC so no encoder motor and has the 4L70E.

I agree with @TollKeeper . You need to drop the TC and see if it's mechanically sound. It sure sounds like it's not working.
 

threefiveleven

Original poster
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Jan 12, 2018
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I really appreciate everyone's help! It looks like I can't be sure without pulling the t-case, but it's more likely the t-case than the trans, and that's a little less harmful to the finances as far as I can tell. A little. It's freewheeling in the driveway right now - in park but completely free to move about, have it blocked up so it can't roll down the drive. I might have time to pull the case this weekend and I'll report back what I find.

Also it looks like at least I can't use that ($100) t-case my friend has, so as much as I was hoping that'd be a solution it's good to know I have to keep searching. And it looks like the NV120 is unique to the TBSS?

I'll give tbssowners a try too.
 

TollKeeper

Supporting Donor
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Dec 3, 2011
8,194
Brighton, CO
@threefiveleven - Now thats interesting that its free wheeling..

If you can, jack up one side of the truck, so that both wheels on one side of the truck are in the air. Spin one of those wheels, does the other wheel spin? If it does, that means the issue is on the front half, before the chain, of the transfer case, or the output shaft on the trans. One is cheaper, the other.... Not so much.

I do need to clarify, if its the output shaft of the trans, I believe the trans has to pulled, and disassembled for that repair. I hope its the interconnect on the front half of the transfer case, for your sake.

@Mooseman - Is there a difference inbetween the AWD tranny in the Rainer/9-7x v8 and the SS/Aero?
 
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TollKeeper

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Dec 3, 2011
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Brighton, CO
@Mooseman - I already answered my own question LOL..

The AWD Rainier/9-7x V8 got the NP4, whereas the Aero/SS got the NR9.

And most others got the NP8 Selectable Transfer case.
 

Mooseman

Moderator
Dec 4, 2011
25,660
Ottawa, ON
The SS is really the bastard child for transfer cases. Because it has a biasing of torque depending on if traction is lost front or back, there is a planetary gearset and other stuff that does this. There could have been internal damage that is allowing no torque to get through it.

We are getting ahead of ourselves here. There is a possibility that the TC's input or the tranny's output shaft may have stripped its splines, similar to how the front diff's intermediate shaft strips. Until you drop the TC, we won't know for sure.

GM supposedly still has them rebuilt but not cheap.
 

TollKeeper

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threefiveleven

Original poster
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Jan 12, 2018
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I was able to get it into the garage this evening and do some spinning of the thingies.

Good news and bad news! The good news is, it's the front differential! The bad news is, it's the front differential!

On one hand, as far as I can tell, the transmission and t-case are both functioning properly. And those both seem very $spendy. (Although, while $1700 for a rebuilt GM unit isn't at all cheap, it's cheaper than I would have guessed!)

Now I'm assuming I'm still looking at a TBSS-only parts situation because of the 4.10's?

And, tell me more about how the 'front diff intermediate shaft strips'... is there some chance it's not the diff itself? It looks like a nightmare to pull that. The front driveshaft spins as you would expect it to.

Thanks btw for everyone's input! Even tho I was off with my trans/t-case guesswork I learned a lot here about what parts are unique to the TBSS. Which seems to be almost everything. lol
 

TollKeeper

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Dec 3, 2011
8,194
Brighton, CO
I have a 4.10 front diff I can sell you That was pulled from a low mileage SS..

But before you get into that, how did you test that you know its the front diff?
 
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threefiveleven

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Jan 12, 2018
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I have a 4.10 front diff I can sell you That was pulled from a low mileage SS..

But before you get into that, how did you test that you know its the front diff?
On jackstands, both driveshafts spin when you put it in gear. With the front driveshaft spinning, neither of the front wheels spin. Minor (but subdued) grumbling from the area of the front diff. Zero connection between the driveshaft and cv axles.
 

TollKeeper

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Dec 3, 2011
8,194
Brighton, CO
That could just be a failed disconnect.

I know there is a thread about it, but I am at work, and cant search right now..

Basically, spin one wheel, either the drive shaft or the other wheel should spin, but usually not both.

EDIT: On the AWD model, the other wheel should spin, but in the opposite direction, no activity on the driveshaft at all. Now if you stop the other wheel from spinning, the remaining wheel in the air should not spin either.

If you can spin both wheels in the same direction, and no driveshaft movement, then either the disconnect has failed, or the diff.
 
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threefiveleven

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Jan 12, 2018
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That could just be a failed disconnect.

I know there is a thread about it, but I am at work, and cant search right now..

Basically, spin one wheel, either the drive shaft or the other wheel should spin, but usually not both.

EDIT: On the AWD model, the other wheel should spin, but in the opposite direction, no activity on the driveshaft at all. Now if you stop the other wheel from spinning, the remaining wheel in the air should not spin either.

If you can spin both wheels in the same direction, and no driveshaft movement, then either the disconnect has failed, or the diff.
Ok yep I can spin either/both front wheels and the drive shaft in any direction I want and there is no connection whatsoever between them.

On the AWD, I see the housing where the 4x4 actuator would mount but of course it's not there. Are the internals still the same, just locked in permanently on the AWD? Meaning, could that still be the failure? I'll start with that side's disassembly.
 

TollKeeper

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Dec 3, 2011
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Brighton, CO
The disconnect is much easier thing to get at, and diagnose (although it can be a real bitch to remove from the side of the oil pan).

What those look like on the inside, and how they operate for the AWD platform, I dont know. Someone with more knowledge than me would have to respond.

I can say they arent cheap, so a good diagnosis would definitely be in order..

Guys on the SS board recommend the Dorman brand surprisingly..

 
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Mooseman

Moderator
Dec 4, 2011
25,660
Ottawa, ON
The regular 4x4 disco has a fork that moves a slip gear to lock the axle to the diff. On the AWD, there is no actuator or fork. It has a sleeve instead of the slip gear that keeps the axle locked. This rarely fails. What does happen is the intermediate shaft gets stripped and also destroys the disco.

Stripped Intermediate Shaft
 
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threefiveleven

Original poster
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Jan 12, 2018
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All, I wanted to update - I finally got around to taking the Blazer apart and it's the intermediate shaft that stripped, and it did indeed chew up the actuator/disconnect. Honestly I'll take it - much better than differential or t-case or trans issues.

Doing a bit of shopping, I see that Dorman has a replacement actuator/disconnect unit for just under $500. I've had good luck with Dorman stuff in general, and I'd buy the Dorman intermediate shaft before I'd buy a GM replacement.

There are also of course $100 disconnect units all over Amazon and ebay, which I doubt I'd trust unless someone here has good experience with it. If it's just essentially a sleeve I could see a cheapo unit working fine. I'd rather replace the sleeve in my original unit tbh but I don't see any rebuild kits.
 

TollKeeper

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Dec 3, 2011
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Hopefully it stripped on the Disconnect side.. Would hate to see all those metal shavings floating around in the diff!
 
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TollKeeper

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Dec 3, 2011
8,194
Brighton, CO
I thought the intermediate shaft was the same irregardless of the model, or gearing... @Mooseman can you confirm?
 
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Mooseman

Moderator
Dec 4, 2011
25,660
Ottawa, ON
The I-shaft is all the same, AWD or 4x4.

I'd have no problem using a Dorman shaft, if they have it, since it's a hard part, however I can't say the same for anything of theirs that's electrical or has moving parts. There is US Powertrain on eBay that has had good results by members here. You have to be sure it's the one without the actuator or fork inside. This is the correct one. They say it's an upgraded version.

 

TollKeeper

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Dec 3, 2011
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Brighton, CO

TollKeeper

Supporting Donor
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Dec 3, 2011
8,194
Brighton, CO
But I do have to put the brakes on a bit here... @Mooseman , or anyone else, check my logic here..

His front axle disconnect on his AWD Trailblazer SS grenaded.

He still should have forward and backward operation out of the setup due to the AWD application, just because of the way a Transfer case is setup. It will always have power going to the rear wheels, regardless of what happens in the transfer case/front axle.

Him not having forward/reverse motion at the rear wheels points to another problem entirely.

If my thought process is correct, his torn up front I-Shaft is just a result of the other problem?
Him being able to free turn the front driveshaft just proves this, doesnt it?

Edit: My thoughts are he has been in FWD for a while, until the I-Shaft grenaded? Now he has nothing, but I could be wrong here.
 
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Mooseman

Moderator
Dec 4, 2011
25,660
Ottawa, ON
It could be different for the SS AWD, which is a full-time system. The transfer case may have self destructed if the front wheels weren't working. I think I read somewhere that if the front wheels aren't working or the front driveshaft is disconnected, it can either prevent the TC from working or damage it, or both.
 

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