Weird 4wd issue goin on.

Darkrider_LS

Well-Known Member
Ok to start off with the system was working fine last night when i went on patrol. But this morning ever since i started running it for the day its been locked in 4wd for the entire day. I can select between A4wd and 4 Hi but i cannot switch it to 2wd or 4lo. I know i am 10K past the interval to change the T case fluid so that is where i will prob start in this process to at least see if the clutches are sticking together causing it to be in 4wd in the T case.

What i know so far:

No service 4x4 light on
No fault codes found on Torque Pro (btw Dmanns i finally spent the $5 and got the pro version lol)
I can select A4wd and 4hi but not 2hi or 4lo

to add a quote from whore thread:

Playsinsnow said:
http://gmtnation.com/f79/4wd-not-working-step-inside-107/




:postcount:



Yeah I thought so.

DRLS: I'm sure you've seen the link above?
With all the above said off to Google i go! I know i found a couple links when i was looking on the phone earlier...Ironically they were some old Trailvoy links where Roadie had spoken in each. Some of the symptoms are similar but some arent...will add to this post when i find them...

Ok this is a thread on a related issue but roadies answer makes me wonder since it does mention the blinking light on the selector switch im seeing.

Stuck in 4 Low

This thread seems to have some answers here as well once again from our resident Roadie

Awd works but not 4x4???????


Ok after reading the two above links they kinda point me in the right direction or at least closer to where to look. The front wheels do spin when power is applied from a stop so from what i read that pretty much eliminates the front disconnect as well as the front actuator along with front diff and drive shaft as the cause. Pointing more and more towards the encoder motor or at the very least dirty or oxidized sensor in the encoder motor...with that all said how difficult is it to change the encoder motor?
 
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Darkrider_LS

Darkrider_LS

Well-Known Member
Playsinsnow said:
"Easy". Hour and a half tops taking your time and breaking for lunch.


GMTNation - How to change a transfer case encoder motor.

Thanks for the info Plays! Now if it wasnt for this damn canadian weather and the lack of a garage or the ramps or the torque wrench needed i would take this on myself. However due to the above i will prob need to try to schedule it into one of the shops here. So when i get free time during the week i will get some quotes for that. But...i will def bookmark this info for future reference if the encoder motor ever goes again after this round. :thumbsup:
 

djthumper

Administrator
Lift up the let side with a jack and then use jack stands. Don't torques it down like armstrong just bring it down snug. man I thought could handle the cold . :wink:
 
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Darkrider_LS

Darkrider_LS

Well-Known Member
djthumper said:
Lift up the let side with a jack and then use jack stands. Don't torques it down like armstrong just bring it down snug. man I thought could handle the cold . :wink:
Im fine with the cold up to a point...a -35 -45C windchill is a lil beyond that point! The other problem lies with the fact that by the time i bought a jack that could lift the TB and jack stands high enough to get under it it would have been cheaper to get it done lol, Not saying i wont eventually buy said equipment. But i do not have it at this time.

On that note would this be the correct Encoder motor for my truck?

http://www.rockauto.com/catalog/moreinfo.php?pk=589974&cc=1441133

Description: DORMAN Part # 600903 {#8890592750, 88996637, 89059275} One of our most popular parts
Fits New Process 226; RPO Code NP8; w/2 Speed Push Button Transfer Case; Rectangular Plug w/7 Pins
 

djthumper

Administrator
That is the correct encoder motor
 
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Darkrider_LS

Darkrider_LS

Well-Known Member
djthumper said:
That is the correct encoder motor
Awesome, I seem to recall a doorman part being mentioned before wasnt sure if that was it or not. So basically ones for the 7 pin application are the selectable 4wds and the 5 pins are the AWDs?
 

djthumper

Administrator
yep that would be correct.
 
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Darkrider_LS

Darkrider_LS

Well-Known Member
djthumper said:
yep that would be correct.
Cool, now its just a matter of putting away the cash to order it and wait for it to come in and save up the money for the install while i do that...so i guess i will essentially be driving in 4hi for the next couple weeks...could be worse..i could be stuck in 4lo or with nothing at all...
 

Playsinsnow

Well-Known Member
I think the Saab, Bravada, Rainer used the 5pins. Different than Envoy/TB.
 
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Darkrider_LS

Darkrider_LS

Well-Known Member

The_Roadie

Founding Member
Administrator
Darkrider_LS said:
I would think the TBSS would use the 5 pin since it was a full time 4wd like the Saab
Mods aren't supposed to guess. :no: The SS has a true full-time AWD, and the transfer case uses a high-end mechanical Torsen T3 style clutch to connect the front and back. It engages smoothly when required, but costs a LOT more than the NP126 A4WD and NP226 4WD (with Lo range) transfer case in the non-SS vehicles. The SS has no encoder motor, for instance.

The Torsen is a true torque sensing system with a higher bias ratio than the NP (New Venture Gear) transfer cases, and the huge difference is it works IN ANTICIPATION OF wheel slip. A wheel slipping SS would be a slow SS.

For more reading:
Torsen T3 Diff explained... - TBSSOWNERS.com Forums - The #1 TrailblazerSS Dedicated Owners Forum

Torsen T-3 Differential
 

Sparky

Moderator
I wouldn't rule out the front disconnect actuator. In both A4WD and 4WD it is engaged. The issue could be when it is trying to disengage the actuator it just doesn't move, so it pops you back to one of the previous modes.

Switching from A4WD to 4WD tells me that the encoder motor is at least somewhat functional. It would seem odd that it would work for some modes but not others.
 
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Darkrider_LS

Darkrider_LS

Well-Known Member
Sparky;223776 said:
I wouldn't rule out the front disconnect actuator. In both A4WD and 4WD it is engaged. The issue could be when it is trying to disengage the actuator it just doesn't move, so it pops you back to one of the previous modes.

Switching from A4WD to 4WD tells me that the encoder motor is at least somewhat functional. It would seem odd that it would work for some modes but not others.
I did have that same thought that it may be the actuator. That would explain why I couldn't go into 2wd.
 

IllogicTC

Well-Known Member
Sparky said:
I wouldn't rule out the front disconnect actuator. In both A4WD and 4WD it is engaged. The issue could be when it is trying to disengage the actuator it just doesn't move, so it pops you back to one of the previous modes.

Switching from A4WD to 4WD tells me that the encoder motor is at least somewhat functional. It would seem odd that it would work for some modes but not others.
He can't get into 4LO either. The actuator stays engaged through ALL modes except 2HI (and maybe the super-secret Neutral?)

Usually since the actuator is just "on" or "off" to the system, it can catch it being a turd. Not always, but usually. If the system has experienced a mechanical failure that is undetectable (let's say, the collar fused to both half-shafts so it's like an AWD unit now), the front axle would remain permanently locked in but as far as the system knows it would still be able to shift to 2HI.

The difference between A4WD and 4HI in terms of range of movement isn't actually all that big. The encoder motor doesn't have to turn all that many degrees to go from minimum clutch application to 100%. But to go to 2HI, it has to bring the motor out below the minimum clutch level. The same thing with 4LO - the raised notch on the shaft is just like the 4HI one, except on the OPPOSITE end of the shaft, so that it can operate the high/low shift.

Switching to 2HI or to 4LO from either of the two middle selections requires the encoder motor to rotate counter-clockwise, at minimum bringing it off the clutch engagement hump on the left side of the lever shaft. Either you have a mechanical failure within the transfer case which is causing the encoder motor to be unable to bring the lever shaft around to 2HI, or you have a jammed encoder motor. It's interesting that no codes have been thrown, but not unheard of. Once you have the encoder motor off you can test the operation of the transfer case manually. Set it to A4WD first, so it'd take maybe 20 degrees of counter-clockwise rotation to bring it to 2HI. If you can't even get the TC to manage that, it's internal to the case, if the shaft can be turned relatively easy (I believe you might be able to feel when the lever shaft stops engaging the clutches because the pin moves to the "low" zone on the lever shaft) then I'd point more toward testing the encoder motor.

And really, I'm leaning toward internal transfer case failure. If the encoder motor's actual position and commanded position don't line up, it's usually good at throwing a code about that, too. Or maybe, just maybe, the TCCM.
 
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Darkrider_LS

Darkrider_LS

Well-Known Member
Larry and I discussed a couple possibilities... One being the encoder motor jamming up internally due to old and cold grease. Bear in mind it started doing this after seeing a week of -20 and colder weather. Plus there is the fact that I have not changed the t case fluid yet so the clutches might be sticking due to this. I'm going to take it into the quick lube on Fri to get the fluid changed. At the very least hopefully I regain normal A4wd function.
 

IllogicTC

Well-Known Member
Darkrider_LS said:
Larry and I discussed a couple possibilities... One being the tccm jamming up internally due to old and cold grease. Bear in mind it started doing this after seeing a week of -20 and colder weather. Plus there is the fact that I have not changed the t case fluid yet so the clutches might be sticking due to this. I'm going to take it into the quick lube on Fri to get the fluid changed. At the very least hopefully I regain normal A4wd function.
TCCM shouldn't be greased, it's the "computer" for the 4x4 :rotfl: You mean front axle disconnect? It could maybe keep you from getting to 2HI but wouldn't stop you from 4LO.

You may be heading in the right direction with sticking clutches. The clutch pack is completely released on both moving to 2HI, and on the way to 4LO (where they just come back together again anyway). Do you use A4WD often?
 
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Darkrider_LS

Darkrider_LS

Well-Known Member
IllogicTC;224021 said:
TCCM shouldn't be greased, it's the "computer" for the 4x4 :rotfl: You mean front axle disconnect? It could maybe keep you from getting to 2HI but wouldn't stop you from 4LO.

You may be heading in the right direction with sticking clutches. The clutch pack is completely released on both moving to 2HI, and on the way to 4LO (where they just come back together again anyway). Do you use A4WD often?
There is a gearbox on the tccm. Tccm standing for transfer case control motor aka the encoder motor. It is this gear box that is greased. And to answer your question I was pretty much using it all winter though I occasionally went back to 2wd on better condition days.
 

Hatchet

Well-Known Member
Darkrider_LS said:
There is a gearbox on the tccm. Tccm standing for transfer case control motor aka the encoder motor. It is this gear box that is greased. And to answer your question I was pretty much using it all winter though I occasionally went back to 2wd on better condition days.
When did they change it from Transfer Case Control Module? The encoder motor is the encoder motor. The TCCM is and electrical box in the cab.



Encoder motor

View attachment 33037

Edit: I also don't see it listed. But have you tried changing the switch? Mine was similar at one point, new switch and i havn't gotten any issues switching modes.
 

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Darkrider_LS

Darkrider_LS

Well-Known Member
Hatchet;224062 said:
When did they change it from Transfer Case Control Module? The encoder motor is the encoder motor. The TCCM is and electrical box in the cab.

Encoder motor

<img src="http://gmtnation.com/attachment.php?attachmentid=20469"/>

Edit: I also don't see it listed. But have you tried changing the switch? Mine was similar at one point, new switch and i havn't gotten any issues switching modes.
Oh... Ok then there is a confusing link or two on here...lol

And no i haven't tried changing the switch yet.
 

The_Roadie

Founding Member
Administrator
Darkrider_LS said:
...then there is a confusing link or two on here....
And you now have the power to fix it, noob mod. :wink:

IME, TCCM has never been discussed as anything but the electronic control module. I standardized on the term "splined disconnect" a long time ago on trailvoy, while GM calls it a bearing housing that's much less obvious.
 
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Darkrider_LS

Darkrider_LS

Well-Known Member
The_Roadie;224270 said:
And you now have the power to fix it, noob mod. :wink:

IME, TCCM has never been discussed as anything but the electronic control module. I standardized on the term "splined disconnect" a long time ago on trailvoy, while GM calls it a bearing housing that's much less obvious.
Hehe mod homework lol. I think part of the confusion is from a chat I had with Larry where I mistakenly assumed tccm was transfer case control motor.

Ok I just had the truck over at the Chevy dealer quick lube where they checked the color of the fluid. It was fine for level but it was a bit darker in color. Plus the tech mentioned he heard a humming noise followed by a click as I tried to change modes. He heard this noise from the encoder motor.
 
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Darkrider_LS

Darkrider_LS

Well-Known Member
Update: A4wd is starting to work normally again now that I got the fluid changed. I can turn normally again. Still binds a bit on really tight turns but at least I can do patrols normally. Kinda makes me wonder about the encoder motor now... It seems to work but maybe it's too weak to make the switch from 4wd to 2wd or to 4lo.
 

IllogicTC

Well-Known Member
Darkrider_LS said:
Update: A4wd is starting to work normally again now that I got the fluid changed. I can turn normally again. Still binds a bit on really tight turns but at least I can do patrols normally. Kinda makes me wonder about the encoder motor now... It seems to work but maybe it's too weak to make the switch from 4wd to 2wd or to 4lo.
So, still no luck on getting it to switch to 2HI? I'd be looking at the encoder motor. Getting a properly-working A4WD looks promising, though. If it can cycle down to the low-end of the adapt ready positions and wasn't before, it's not too far from being able to get into 2HI.
 
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Darkrider_LS

Darkrider_LS

Well-Known Member
IllogicTC;225326 said:
So, still no luck on getting it to switch to 2HI? I'd be looking at the encoder motor. Getting a properly-working A4WD looks promising, though. If it can cycle down to the low-end of the adapt ready positions and wasn't before, it's not too far from being able to get into 2HI.
At this point it switches rapidly between a4wd and 4hi, plus as said I can actually make tight turns now which is great since I need be able to do that in the parking garage I patrol.
 

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