NP241 vs NP243

[Mkuhn138]

My K5 is being built as a prerunner with TTB suspension, and consequently need to swap out my TC with Drivers-side drop unit. It's going behind a 700r4 with hydraulic lockup. I will really only be using 4x if I get stuck, or possibly if I'm on Icy roads in the winter. I was originally planning on a 241 but really am intrigued by the idea of the 243 due to the electronic shift - mainly bc I prefer to not have a shift lever; I'm fabricating a custom center console prefer to build it as clean as possible. My concerns are:

-Will a SYE kit intended for a 241 work on a 243?
-Will the 243 work without an ECU or factory gauge cluster?
-Is this an idiotic idea?

I know the electronic shifters/encoders go out from time-to-time, but am not so worried about that. Also, will not be towing this truck so Neutral is not much of an issue. I just don't want to introduce something that's gonna need a stand alone module or a bunch of oddball wiring. Literally all of the factory engine control and gauges are gone and I'm running a Holley ECM and other stand alone equipment. Any insight is much appreciated.

 

[Larry]

My K5 is being built as a prerunner with TTB suspension, and consequently need to swap out my TC with Drivers-side drop unit. It's going behind a 700r4 with hydraulic lockup. I will really only be using 4x if I get stuck, or possibly if I'm on Icy roads in the winter. I was originally planning on a 241 but really am intrigued by the idea of the 243 due to the electronic shift - mainly bc I prefer to not have a shift lever; I'm fabricating a custom center console prefer to build it as clean as possible. My concerns are:

-Will a SYE kit intended for a 241 work on a 243?
-Will the 243 work without an ECU or factory gauge cluster?
-Is this an idiotic idea?

I know the electronic shifters/encoders go out from time-to-time, but am not so worried about that. Also, will not be towing with this truck so Neutral is not much of an issue. I just don't want to introduce something that's gonna need a stand alone module or a bunch of oddball wiring. Literally all of the factory engine control and gauges are gone and I'm running a Holley ECM and other stand alone equipment. Any insight is much appreciated.

Yes, this is very idiotic. Don't know why anybody in their right mind would want to swap on electric shift . Prerunner in California explains a lot though

 

[rjfguitar]

Gee, big help to the guy there.


Anyway, I'm not real up on the newer cases, but I could see an issue if the 243 is the one with the "auto" 4wd feature. I'm pretty sure that there is a module for the Tcase and it needs to communicate with the PCM for info like mph and likely abs.

I like the idea though, while most of us prefer a manual shift case, I do like bells and whistles and an electric shift could be interesting.

 

[fourxpete]

yes the sye will work on the 243 as far as wiring i'm not 100% sure on the activating the motor i believe its like a window motor positive polarity goes one way reverse polarity goes other way i'll check my wiring diagram tomorrow on my 243 it has 3 plugs on it one for activating motor one for 4wd activation and last plug for vss same tone ring as 241

 

[Hogback Fabrication]

Anyway, I'm not real up on the newer cases, but I could see an issue if the 243 is the one with the "auto" 4wd feature. I'm pretty sure that there is a module for the Tcase and it needs to communicate with the PCM for info like mph and likely abs.

The "auto 4WD case" is the 246, the 243 is just a 241 with an electric motor to shift it. Should be easy enough to adapt, but likely not much info out there on how to do it.

 

[rjfguitar]

The "auto 4WD case" is the 246, the 243 is just a 241 with an electric motor to shift it. Should be easy enough to adapt, but likely not much info out there on how to do it.

THanks for the clarification. I liked that auto 4wd feature in the wife's old Yukon.

 

[Larry]

Don’t forget you would also need a Transfer Case Control Module to operate an electric shift tcase. The 243 is not a straight out 241 with an electric motor on it although much of it is the same. When I lived in Detroit and worked at GM these 243’s and 246’s were the new thing. I spent a 6 month rotation on GM’s tech service line where the electric shift garbage was the #1 call into our group at the time. Especially when the NP8 Autocrap tcase came out. Talk about a train wreck. Swapping this garbage on to an older 4x4 would be almost as bad as buying a K30 and removing the D60 and 14FF to install a pair of 10 bolts to save weight. Not a good idea.

Anyway, here is the component description from the GM service manual.

The New Venture Gear Model NV243 is an electronically controlled optional transfer case for use on four wheel drive K trucks. The driver selects 2HI, 4HI, or 4LO by pushing one of three illuminating shift select buttons mounted on the instrument panel. The shift select buttons display the transfer case mode and range, self-test, diagnostic trouble codes, and electronic shift mechanical engaging problems.

During normal driving the transfer case is in the 2HI mode. When the transfer case is in the 2HI mode. When the transfer case is in 2HI both the 4HI and 4LO switch circuits are open, and both lights are OFF. When the four–wheel drive shift select button has been pressed, the four–wheel drive indicator lamp under the sift select button turns ON when the front axle has engaged. The shift select button will blink while the front axle is engaging. This is a normal condition.

The shifting of the transfer case is performed by a motor/encoder that receives drive signals from the transfer case control module (TCCM). When the driver selects one of the transfer case shift select buttons, request signals are sent to the TCCM. If the correct input signals exists, the TCCM will send drive voltages to the motor/encoder. The motor/encoder will position the transfer case to the ordered shift position.

 

[Blue85]

You can't just wire a toggle switch to it because the motor needs to park the linkage in 4 distinct positions. That's what the encoder and controller are for. Even if you were just trying to get to the "end" positions by holding the switch for a long time, there is always the chance that it doesn't really move all the way (especially a risk when moving between ranges). Then where exactly are the shift forks? In that case, the controller will back it off to the last position so you don't grind on things by driving with the forks in some intermediate position.

If the TC controller is a stand-alone unit, the whole system could probably be swapped over.

An alternative would be to build some kind of custom linkage that moves the shifter over to somewhere else you like.

 

[jekquistk5]

Or you could use a small plc to handle the encoder outputs and drive the steppers. The program shouldn't be that hard to write.

 

[sreidmx]

Id do what Jek is saying, its probably got some PWM control going on to engage it.. why not find a manually actuated case and run the cable shifters? this would eliminate these issues all together.

You could use a ardrnio to control the motor.

 

[Stomis]

If the name of the game is not having a lever than why not build some sort of solenoid to shift the 241 linkage. At least if you're screwed and something breaks you can manually shift it.

 

[Russell]

I think the older 90s NP243s were fairly standalone in their operation. As mentioned you'd need to install a transfercase control module but I bet the hookup would be pretty straight foward. I doubt it would be looking for more than power, ground, front axle position indication, park / neutral indication, park brake indication and maybe service brake indication. I'll try to remember to look up some diagrams tonight...

EDIT:

These are the diagrams for a 97 Chevy Tahoe with an NP243. Looks like the only thing I missed is a speed input from your DRAC. This would be a fairly easy transfer case to install electrically speaking.

 

[Blue85]

Looks like it's pretty much stand-alone. It looks like the connections to the PCM are just shared signals. You would probably have to put a resistor in place of the front axle actuator to fake out the controller. Then you can probably fake the front axle switch by shorting. Whatever the transfer case synchronizer is, it must be built in. Then you need vehicle speed.... Not sure if no signal would be interpreted as 0MPH or if it faults out never seeing an input. It can't really be doing much open/short diagnostic on that line since so many devices on the vehicle usually use it.

 

[Russell]

Looks like it's pretty much stand-alone. It looks like the connections to the PCM are just shared signals. You would probably have to put a resistor in place of the front axle actuator to fake out the controller. Then you can probably fake the front axle switch by shorting. Whatever the transfer case synchronizer is, it must be built in. Then you need vehicle speed.... Not sure if no signal would be interpreted as 0MPH or if it faults out never seeing an input. It can't really be doing much open/short diagnostic on that line since so many devices on the vehicle usually use it.

I have no idea what the K1 / K2 / K3 codes stand for. Seems to be front diff related.

The front actuator signal is just a ground signal. When the t-case is in 2wd or neutral that switch is open. When in 4wd high or low it also is grounded. Just feed that same signal straight into the TCCM and I bet it'd be perfectly happy with that. I'd recommend installing a DRAC to take the VSS signal and convert it into the 4000 pulse per mile signal that the TCCM is looking for since you no longer have a vehicle speed indication. If you wanted to install a speedometer again the DRAC will provide the speed signal one is looking for as well.

The TCCM wants to see 12V applied to pin D2 when the transmission is in park and ground connected to pin D16 when in park or neutral.

 

[82355]

Seems like a lot of horsing around to add a failure point.

Martin

 

[Larry]

I have no idea what the K1 / K2 / K3 codes stand for. Seems to be front diff related.

K1, K2 & K3 are abbreviations for ½ ton 4x4 (K1), ¾ ton 4x4 (K2) and 1 ton (K3). Then there are C1 (2wd 1/2 ton), C2, C3, etc. They used the two digit lingo in a lot of engineering documents and wiring diagrams.

Seems like a lot of horsing around to add a failure point.

Martin

That is a for damn sure!

 

[Mkuhn138]

Thank you everybody for the responses and knowledge you've shared - it's incredible how much wisdom is floating around on this board... Holy **** - I had no idea there was so much other non-sense involved... I kind of assumed it was a just a 241 with an E-shifter that maybe required a ground or voltage signal to shift.

I picked up 241c this morning off of a 94 truck - grabbed it for $100... I will run the JB Fab cable shifter with it and keep things as clean as possible.

On a separate subject, does anybody aside from HAD make an ebrake kit for the 241? I want to see what others may be charging - though i couldn't seem to find any with a simple google search. It seems like it would actually be fairly easy to have a rotor cut that bolts to a CV flange and fab up a bracket - but not sure if it's worth the trouble to save a few bucks...