4WD to AWD Swap

[drdave81]

Has anyone done this? Specifically using an NP149 transfer case. This is in my Silverado, but it would apply to any 4WD vehicles. I've seen some talk that you can shift the vehicle into 4WD, then just disconnect everything and the front axle will stay locked in. This would be the easiest for me, since my truck has a 3.42 rear gear, and all the Denalis and Escalades came with 3.73 up front. I don't have to worry about regearing right now.
Also, I keep seeing conflicting info on the front driveshaft being different length between the two set ups, whether you have to use the AWD front driveshaft, or can use the existing NP246 driveshaft.

 

[rockola1971]

An AWD system works very different from a 4wd system internally to the Tcase. A 4wd system is not designed to be run on dry pavement continuously. An AWD system is designed to be able to run continuously on dry pavement and that is because the AWD Tcase is very different from a 4wd Tcase internally. To do a conversion would require more than just the hard pieces like the Tcase, Driveshaft, etc. You would also need Tcase control module, wiring harness, etc for the AWD too. There is a piece of hardware that bolts on the front diff and locks it in forever (until removed). This hardware replaces the shift motor at the front diff.
Im not sure why you want to be in 4WD all the time assuming you are daily driving this truck. That thing will be wheel hopping all over the place in turns, especially low speed turns. An AWD does not do that because of the built clutch slip of its Tcase. New Process makes the 4wd Tcase and Borg Warner makes the AWD Tcase.

 

[Mudsport96]

An AWD system works very different from a 4wd system internally to the Tcase. A 4wd system is not designed to be run on dry pavement continuously. An AWD system is designed to be able to run continuously on dry pavement and that is because the AWD Tcase is very different from a 4wd Tcase internally. To do a conversion would require more than just the hard pieces like the Tcase, Driveshaft, etc. You would also need Tcase control module, wiring harness, etc for the AWD too. There is a piece of hardware that bolts on the front diff and locks it in forever (until removed). This hardware replaces the shift motor at the front diff.
Im not sure why you want to be in 4WD all the time assuming you are daily driving this truck. That thing will be wheel hopping all over the place in turns, especially low speed turns. An AWD does not do that because of the built clutch slip of its Tcase. New Process makes the 4wd Tcase and Borg Warner makes the AWD Tcase.

I believe he is referring to using a awd case, and using the 4hi button to engage the front axle. Thus using the disconnect style front diff with the awd case. And at thatbpoint it would function just as a normal AWD system. Which, for a little while will work. But eventually the passenger side shaft will fail. This is the exact opposite of what the ZR2 community used to do. We would use bravada awd stub shafts in the front to eliminate the weak link disconnect that would leave you stranded with 2wd at the worst time. Especially if you had installed a locker in the tiny 7.2 front diff.

What the OP needs to do is get an awd case and front diff, and just change out the passenger side stub shaft with his disconnect shaft. No gear change needed OP.

 

[rockola1971]

I believe he is referring to using a awd case, and using the 4hi button to engage the front axle. Thus using the disconnect style front diff with the awd case. And at thatbpoint it would function just as a normal AWD system. Which, for a little while will work. But eventually the passenger side shaft will fail. This is the exact opposite of what the ZR2 community used to do. We would use bravada awd stub shafts in the front to eliminate the weak link disconnect that would leave you stranded with 2wd at the worst time. Especially if you had installed a locker in the tiny 7.2 front diff.

What the OP needs to do is get an awd case and front diff, and just change out the passenger side stub shaft with his disconnect shaft. No gear change needed OP.

I would think that running the AWD with that funky setup which unloads the front output shaft of the Tcase would cause problems. It essentially would almost be exactly like lifting a AWD up on a vehicle lift and running it but with 2 wheels unloaded(the front) instead of all 4. As far as using the original 4x4 button to control the front shift motor you could easily just remove the OEM wiring from that part of the switch and run a 12v ignition only wire from fuse box to the switch and then connect the other side to a wire that goes to the front diff shift motor. That would prevent from having to get the AWD stub half for the front diff and save alot of work. Id have to check the schematics but I believe it is 12v+ seeking instead of ground seeking.

 

[Mudsport96]

Using the 246 case in AUTO mode would see some issues for sure. But I believe using the NP149 and locking the front diff collar in the engaged position would operate the same as any "normal" Denali AWD system. However, the collar was never designed to take that kind of abuse. So it will eventually fail, and it WILL be at the most inopportune time.

 

[rockola1971]

Using the 246 case in AUTO mode would see some issues for sure. But I believe using the NP149 and locking the front diff collar in the engaged position would operate the same as any "normal" Denali AWD system. However, the collar was never designed to take that kind of abuse. So it will eventually fail, and it WILL be at the most inopportune time.

The NP149 uses a viscous coupling sealed unit to act as the clutch between the front and rear diff on an AWD system. The torque bias is 62% rear 38% front. If the front or rear is unloaded to the viscous clutch (as in our hypothetical NP246 setup front diff being used as a switchable lock/unlock front diff scenario) the outcome would be catastrophic to the viscous clutch. Lots of bad noises and fragging the Tcase. This is why an AWD MUST be towed with all 4 wheels on a flatbed instead of front wheels on a dolly. Unless of course the rear driveshaft is disconnected while on a dolly.

So the best bet for a swap is use the existing NP246 setup and lock the front diff "permanently" with the available aftermarket part that takes place of the front diff shift motor or use an AWD front diff stub like you mentioned.

 

[drdave81]

I know how the transfer cases function internally. I'll try to clarify what my plan is. I will be removing the 246 t case and installing the 149 t case. I will lock the front axle using the actuator, so it is essentially just like the denali/escalade front axle. Then remove everything related to the 4x4 system; wiring, switch, control module. This would leave me with basically the same set up as what the denali/escalade has. No electronics (00-02 Denali and 02 Escalade).
What my question was, is are the front driveshafts between the 149 and the 246 the same. I've seen conflicting info about them being different lengths. And, I've come across another question, once the front axle is actuated, so it is locked...... if I disconnect the wiring connector, will it stay locked or not. I'll find that one out myself in a couple days once I'm done driving a company vehicle, my truck is sitting at work, so I can't test this out on it.

Edit: I saw rockola1971's comment about the actuator. So it sounds like it needs a constant 12V to stay locked. So if I unplug the connector, it will unlock the front axle. Still, running a 12V supply would be simple enough, rather than swapping out the right side of the front axle.

 

[Mudsport96]

I know how the transfer cases function internally. I'll try to clarify what my plan is. I will be removing the 246 t case and installing the 149 t case. I will lock the front axle using the actuator, so it is essentially just like the denali/escalade front axle. Then remove everything related to the 4x4 system; wiring, switch, control module. This would leave me with basically the same set up as what the denali/escalade has. No electronics (00-02 Denali and 02 Escalade).
What my question was, is are the front driveshafts between the 149 and the 246 the same. I've seen conflicting info about them being different lengths. And, I've come across another question, once the front axle is actuated, so it is locked...... if I disconnect the wiring connector, will it stay locked or not. I'll find that one out myself in a couple days once I'm done driving a company vehicle, my truck is sitting at work, so I can't test this out on it.

Edit: I saw rockola1971's comment about the actuator. So it sounds like it needs a constant 12V to stay locked. So if I unplug the connector, it will unlock the front axle. Still, running a 12V supply would be simple enough, rather than swapping out the right side of the front axle.

You could also hit the junkyard and get an actuator to disassemble and see if you can make a way to manually lock it in place so you don't need a constant 12v. But you will eventually kill the lock collar on the 4x4 shaft. Like Thanos, it is inevitable. So you need to start searching for an awd shaft to swap.

 

[Mudsport96]

The NP149 uses a viscous coupling sealed unit to act as the clutch between the front and rear diff on an AWD system. The torque bias is 62% rear 38% front. If the front or rear is unloaded to the viscous clutch (as in our hypothetical NP246 setup front diff being used as a switchable lock/unlock front diff scenario) the outcome would be catastrophic to the viscous clutch. Lots of bad noises and fragging the Tcase. This is why an AWD MUST be towed with all 4 wheels on a flatbed instead of front wheels on a dolly. Unless of course the rear driveshaft is disconnected while on a dolly.

So the best bet for a swap is use the existing NP246 setup and lock the front diff "permanently" with the available aftermarket part that takes place of the front diff shift motor or use an AWD front diff stub like you mentioned.

I get what you are saying, bit I think you are missing the point of him LOCKING the 4wd shaft in 4x4 position.

 

[rockola1971]

I get what you are saying, bit I think you are missing the point of him LOCKING the 4wd shaft in 4x4 position.

You are correct. Im not understanding what the OP's actual end game is here. Locking the front axle then "disconnect everything"???? Using the 4hi button later to engage/disengage the front axle that is ultimately connected to a AWD Tcase....that wont end well for the viscous coupler.