246 transfer case no power to front wheels 4x4 slip?

W8MCC · January 18, 2019

1998 suburban 1500 4x4 5.7 4l60e np246 push button 4x4 2/4hi/4lo/auto

I need some help here. Suddenly my 4x4 quit working on my truck, details above. I have diagnosed everything I can. There are no codes or lights.

The issue is no power to the front wheels while in any of the 4x4 positions. The front axle actuator is working, checked with a new one. The encoder motor is new, just installed oem motor.

When the truck is on stands the front wheels roll in 4x4 but on the ground they have no torque. I put the front on the ground and jacked up the rear axle, the rear tires spin in drive, the fronts have no pull what so ever.

With the truck in the air, 4x4 hi engaged, engine off, truck in neutral, I can roll the front drive shaft by hand and see movement in the rear shaft. Again, when it's in the air everything works, only on the ground it acts like it's still in 2wd.

Does the 246 have slipping issues? Is that even possible? I've never had one apart but if there's discs to engage them possibly they are worn?

My next step is a xfer case but I don't want to throw any more money away.

I should mention I have this problem in auto mode too.

Thanks

mjm-1957 · January 18, 2019

What happens in 4 low?

W8MCC · January 18, 2019

16 minutes ago, mjm-1957 said:

What happens in 4 low?

The truck shifts to low but still no front wheel assist. Confirmed on the ground and in the air

Also I had another test I didn't mention; I placed a 2x4 in front of the front tires on a patch of ice. Drop it in gear and the rear tires spin on the ice. No front wheel torque in 4 hi, 4 lo, or auto.

The front does roll when all 4 wheels are in the air. It's like there's just enough friction to appear like it's working in the air but nothing on the ground.

Calling for a foot of snow tomorrow... can get a xfer case today from local junkyard. But making sure I'm not missing anything first.

carkhz316 · January 18, 2019

The clutches in the 246/ Autotrac transfer cases give you partial or full torque to the front axle. If they are fried or slipping, you will loose power to the front axle. The in the air test works because of either parasitic drag in the transfer case, or the little bit of grip the clutches have left. If you were to grab the front, you would likely be able to stop the wheels/ driveshaft.

How is the fluid/ level in the T-case?

W8MCC · January 18, 2019

3 minutes ago, carkhz316 said:

The clutches in the 246/ Autotrac transfer cases give you partial or full torque to the front axle. If they are fried or slipping, you will loose power to the front axle. The in the air test works because of either parasitic drag in the transfer case, or the little bit of grip the clutches have left. If you were to grab the front, you would likely be able to stop the wheels/ driveshaft.

How is the fluid/ level in the T-case?

I haven't checked the fluid level. If it is low it's probably smoked the clutches then anyway. Or are you saying that fluid is required to keep pressure on the clutch pack?

mjm-1957 · January 18, 2019

The clutch pack is applied mechanically.The front and rear driveshafts are locked together in 4 low, thats why I asked what it does in that range,are you sure the front axle is engaged?You should not be able to turn the front driveshaft if the actuator plunger is pushing the shift fork all the way in. You can also take the actuator out and physically move the fork with a screw driver and make sure nothing is binding or broken.Hope this helps.

W8MCC · January 18, 2019

2 minutes ago, mjm-1957 said:

The clutch pack is applied mechanically.The front and rear driveshafts are locked together in 4 low, thats why I asked what it does in that range,are you sure the front axle is engaged?You should not be able to turn the front driveshaft if the actuator plunger is pushing the shift fork all the way in. You can also take the actuator out and physically move the fork with a screw driver and make sure nothing is binding or broken.Hope this helps.

Yes I believe the front axle is fully engaged. I also replaced the front axle actuator.

Truck on ground, engine off, 4x4 engaged, trans in neutral, turn front drive shaft with a prybar and the truck will roll forward.

I swear it's got to be in the xfer case. Even in low I have no front wheel torque on the ground.

W8MCC · January 18, 2019

Are the clutches used in 4 low? Could they be so worn that what little resistance there is in the air can be overcome by being on the ground? What am I missing? Does the oil pump provide pressure to something or just for lubricant??

g2full · January 18, 2019

Out there suggestion.. but I have noticed issues with the shift buttons on these years. Are the lights on your buttons lighting up? My uncle has a 96 Tahoe and to get his to shift you have to push in on the dash by where the buttons are or it won't work. He isn't worried about it, so he's never looked into fixing it but I imagine it's an issue with the switch.

W8MCC · January 18, 2019

4 minutes ago, g2full said:

Out there suggestion.. but I have noticed issues with the shift buttons on these years. Are the lights on your buttons lighting up? My uncle has a 96 Tahoe and to get his to shift you have to push in on the dash by where the buttons are or it won't work. He isn't worried about it, so he's never looked into fixing it but I imagine it's an issue with the switch.

Buttons are lit and functional.

mjm-1957 · January 18, 2019

The oil pump is only there to provide lube oil. The clutch pack only is used in auto 4wd.

W8MCC · January 18, 2019

16 minutes ago, mjm-1957 said:

The oil pump is only there to provide lube oil. The clutch pack only is used in auto 4wd.

Is it possible to have a wasted clutch pack and still get 4x4 hi?

mjm-1957 · January 18, 2019

If you are in 4w high or low and not getting any action from the front driveshaft im sorry to say you will have to go inside the transfer case. When you had the encoder motor off did you try shifting it manually?I have had a few with broken shift fork parts and also a worn roller that rides on the cam not allowing full motion of the shift fork but it also was grinding, and you didnt mention any noises.

W8MCC · January 18, 2019

9 minutes ago, mjm-1957 said:

If you are in 4w high or low and not getting any action from the front driveshaft im sorry to say you will have to go inside the transfer case. When you had the encoder motor off did you try shifting it manually?I have had a few with broken shift fork parts and also a worn roller that rides on the cam not allowing full motion of the shift fork but it also was grinding, and you didnt mention any noises.

4x4 works in the air on jack stands not on the ground no ppwer from the front wheels. The case is silent, I can hear shifting and feel the motor (s) actuating by hand. Everything is working freely. My issue is with no torque being applied to the wheels whIle under a load.

Thoughts? Clutch?

mjm-1957 · January 18, 2019

Take the rubber plug out on the tail housing and get a mirror and a light and see if the snap ring that holds the rear output bearing is still in one piece. That snap ring can break and let everything move rearward and possibly cause the issue you are having.

Edited January 18, 2019 by mjm-1957