2WD Lo??

TJBaker57

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Aug 16, 2015
2,897
Colorado
I read an old thread here batting around the idea of a 2 Lo range. Looks like the thread dropped away without resolution. I saw this last year on my Tech 2 in a few videos and today I isolated the encoder voltage return range where it displays. Anyone have any notion why this would even be in the Tech 2 if it is not even possible as Roadie stated??

PXL_20210919_193432046~2.jpg
 

azswiss

Member
May 23, 2021
860
Tempe, AZ
Here's a shot in the dark. A single motor/encoder assembly actuates two separate physical transitions inside the T-Case: 2wd/4wd & Hi/Lo. The T-Case on my CJ7 uses a simple linkage to manage both transitions from a single shifter lever. I wonder if there is an internal sensor for each specific shifter linkage and one of them (2wd/4wd??) is stuck/sloppy or the sensor is iffy????

Edit: Just watched a tear down of a NP246 and no internal sensors, just gears, bearings, shift forks, etc. so the sensor idea is not valid.
 
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Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Was that from putting the switch to a particular position or was it commanded by the Tech 2? It could be a position that's only for diagnostic purposes.

Or maybe it's saying 2wd lo because the disconnect is not engaged?
 

TJBaker57

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Aug 16, 2015
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Colorado
This was derived by substituting a 10 turn potentiometer in place of the encoder sensor ring. It was done on the bench for the purpose of establishing what sensor output range results in the Tech 2 reading out which operational range. I slowly adjusted the pot to see where the Tech 2 would display the various operational states.

This looks a little awkward because I was working my way from the hex of the PID return to the range reported by the Tech 2 and then added the voltages as an afterthought.

Screenshot_20210919-211956.png


Having studied the operational document of the transfer case it appears to me that it may work like this: As the encoder shifts from 2Hi to 4Lo it moves first to neutral, then to this "2 Lo" position and then engages the clutch pack for 4Lo.
 
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Mooseman

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Dec 4, 2011
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Interesting. So just a transitional reading however could indicate a problem if it stays there in actual operation.
 

TJBaker57

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Aug 16, 2015
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I think I once saw a calibration update note for some adjustment in this area?

Seeing it in the Tech 2 makes me wonder if the position is mechanically operational. Or would it be prone to "slipping out" back to neutral.
 

TJBaker57

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Aug 16, 2015
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Just went a couple times around the block (slowly) in 2 Lo!! Sets a code for encoder malfunction but that's not surprising given the means by which I am getting 2 Lo. And I don't always get it either. Needs more investigation, Also not sure about how much strain I would want to put on it without seeing exactly where the components are inside with regard to engagement.

I don't even have a use for it but thought I would see if it worked.
 

TJBaker57

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Aug 16, 2015
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Colorado
In this video the author references the 2Lo phenomenon as part of his conversion from push-button to manual shifting on a NP246 T-Case in a '98 Tahoe.
Np246 manual conversion


So the difference between what this video shows and what I did today is this: his 2 Lo has the transfer case front propshaft drive engaged and the front axle disengaged where what I did has the front axle engaged but the transfer case has not applied the clutch to the front propshaft.
 

Reprise

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Just read thru this and see that there really seems to be a '2 Low' as a separate range - ? Since I know the OP knows what he's doing, I'll take that as a 'yes'. :yes:

I looked at that Tech2 display and interpreted it as '2 - Low' (indicating one of two total ranges, 'low' and 'high', vs. indicating separate modes (2 High, 4 High, 4 Low, etc.) But that's just from looking at that screencap, not by actually hooking my own up and doing anything with it (because I'm lucky to use 4WD on two trips a year, IF I'm driving in a heavy snowfall).
 

TJBaker57

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Aug 16, 2015
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Colorado
just from looking at that screencap,

So here is a little more than a screengrab. Seen here I adjust a Transfer Case Range Position Sensor, showing the various displays from the Tech2 for various rotations. For those who have never seen this sensor it is located inside the encoder/motor beneath the insulator/seal..

IMG_20190701_125024.jpg

 
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santon

Member
Jun 3, 2020
93
Israel
Just went a couple times around the block (slowly) in 2 Lo!! Sets a code for encoder malfunction but that's not surprising given the means by which I am getting 2 Lo. And I don't always get it either. Needs more investigation, Also not sure about how much strain I would want to put on it without seeing exactly where the components are inside with regard to engagement.

I don't even have a use for it but thought I would see if it worked.
Have you managed to command the motor to move to particular position or just used a potentiometer instead of the encoder to get a voltage range identified as "2 Lo" ?

As another way of getting 2 Lo, I think it would be possible to make a module that will command the axle actuator to disengage the right wheel in 4 Lo on demand, without letting the TCCM know about that.
 
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TJBaker57

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Aug 16, 2015
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Colorado
Have you managed to command the motor to move to particular position or just used a potentiometer instead of the encoder to get a voltage range identified as "2 Lo" ?

As another way of getting 2 Lo, I think it iwould be possible to make a module that will command the axle actuator to disengage the right wheel in 4 Lo on demand, without letting the TCCM know about that.

The idea of circumventing the front axle disconnect circuitry seems like a fairly easy thing to do with a switch and/or relay to break the control line from TCCM to the front axle disconnect actuator while maintaining the disconnects status switch signal.

As a proof of concept sort of thing I did manage to position the encoder/motor to the 2 Low signal position as previously identified by a Tech 2 and drove around a little to confirm I had rear wheel drive only and low range as well. The process had a low success rate achieving the goal twice in 8 or 10 attempts. And even with a successful transition to 2 Low I set an encoder malfunction code of C0327.

What I did was to connect a particular resistance between the encoder signal to the TCCM and the low reference. This parallel resistance drops the signal voltage that the TCCM sees and uses to position the shift motor. Thus the signal then seen by the TCCM would be offset from the true shift motor position. I wanted to have the encoder signal at the TCCM read in the 4 Low range of 0.49 to 0.80 vdc while the encoders actual unmolested signal voltage was at the 2 Low range of 0.82 to 1.24 vdc, ideally favoring the lower end for more engagement of the low range gearing.

I connected the added resistance during a shift from 2 High to 4 Low. I tried to time the connection to when I heard the shift motor in motion. I could hear the shift motor jockeying around a bit. And the C0327 code sets pretty quickly, possibly even immediately upon the added resistance connection. I suspect the code sets as a result of the abrupt change in encoder signal voltage seen by the TCCM.

On the two 'successful' attempts I read 1.14 vdc and 0.98 vdc at the signal line to the TCCM. I don't know if the TCCM actually positioned the shift motor there or not. The dash display would display 4 Low and the only indication something was not 'factory correct' was the Service 4WD light.

I do NOT advise anyone to attempt this !! In my case it is a second vehicle and available for such shenanigans. On the failed attempts I ended up in 4 Low normally and at least once the Transfer Case slipped out of my intended position and grinding gears were heard as it was between engagement and neutral. Sometimes I would drive about 50 yards or so and then slip into neutral.
 
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santon

Member
Jun 3, 2020
93
Israel
The idea of circumventing the front axle disconnect circuitry seems like a fairly easy thing to do with a switch and/or relay to break the control line from TCCM to the front axle disconnect actuator while maintaining the disconnects status switch signal.
Right, once the car is in 4 Lo, breaking the control line from TCCM to the actuator will cause it to retract. However, the disconnect status signal (12V from the actuator to TCCM) will be interrupted so one need to maintain it using another relay, or by other means. This mod is relatively easy to do and I wanted to try it though I am not compeletly sure about the usefulness of it.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
The real question would be, why would anyone need or want 2lo? I hardly, if ever, use 4lo so 2lo would be ???
 

TJBaker57

Original poster
Member
Aug 16, 2015
2,897
Colorado
The real question would be, why would anyone need or want 2lo? I hardly, if ever, use 4lo so 2lo would be ???


Agreed it would be of rare use, as Roadie stated here...



As for "why would anyone need or want" I ask myself this question every time I hear some obnoxiously loud butchered exhaust system or equally obnoxious boom boom boom box roll by!! :wink:
 

santon

Member
Jun 3, 2020
93
Israel
The 2Lo could be potentially useful for tight maneuvering and heavy towing on pavement. I came across several threads on other forums on different 4x4 vehicles (e.g., Ford, Suzuki) where similar mods were discussed. Not sure whether any 4x4 vehicle was ever equipped with 2Lo from the factory.
 

azswiss

Member
May 23, 2021
860
Tempe, AZ
I would be concerned about higher torque loads thru the rear driveshaft, u-joints, etc. Especially under sudden acceleration/deceleration. All in all, though, love this kind of experimentation!
 

TJBaker57

Original poster
Member
Aug 16, 2015
2,897
Colorado
Not sure whether any 4x4 vehicle was ever equipped with 2Lo from the factory.

That's the sort of thing that makes me wonder, just why did someone specifically write the Tech 2 software to display this "2 Low" at this specific range of encoder sensor values and shift motor location.

Puzzling!!
 

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