2WD not working. . . .

[Krazny13]

Alright, I've been pulling my hair out on this one, figured I'd ask for some expert advice. . .

Long story short, my 2WD mode in my AWD/4WD 2002 TB doesn't work. AWD and 4HI/LO work fine, and I've been driving it in AWD mode to get around. When I put it into 2WD mode, it'll work for anywhere from 10 feet to 20 miles, then for some reason it seems like the transfer case neutralizes, and I have no power to any of the wheels. No codes, no flashing lights, no service now signs, nothing. If I coast to a stop, neutralize the transmission, and put it into AWD, it'll function fine. Not taking it out of gear results in a grinding noise, before resuming normal AWD function. Its been updated with the latest software - no joy on a solution. Short of tossing it up on a lift and tearing apart and completely replacing the lower powertrain, I'm out of ideas.

Thanks for any info in advance.

 

[djthumper]

How many miles are on the vehicle? When did you last change the fluids? They should be done every 50K for the transfer case. Please fill out your vehicle profile for others to easily reference and it is there for future posts.

It could possibly be the 4WD switch or the encoder motor. It isn't very often that 2WD doesn't stay engaged.

 

[Krazny13]

How many miles are on the vehicle?

117k or so.

When did you last change the fluids?

Would have been done around 88k or so. It hadn't been used much, 3-5 miles every couple of weeks for groceries for almost 6 months before I bought it.

It could possibly be the 4WD switch or the encoder motor.

Hmm. Any way to check the switch?

It isn't very often that 2WD doesn't stay engaged.

Tell me about it. Nothing I've found so far on my own has come close to this problem. Its always 4WD/AWD that won't work.

 

[djthumper]

The switch is relatively cheap but you can always try cleaning the contacts buy rotating the switch a bunch of times I would also listen for the motor for any odd noises. I am sure the roadie will have more when he comes along.

 

[The_Roadie]

Good morning, folks.

It can't be the switch unless you're not seeing the clue. Switch failures usually come with a Service 4WD light on the dash, or a flashing mode light on the switch. I assume your switch always stays lit on 2WD mode during these events? I can imagine a rare failure mode where the switch looks to the TCCM like you've selected "Neutral" mode (to the far right clockwise), but that mode is heavily interlocked and I can't imagine the transfer case entering neutral mode inadvertently. You'd see it on the mode light on the switch anyway.

See the theory of operation article for the transfer case here: Offroadtb.com Transfer Case Operation: NVG 226 (NP8)

I see NO physical way for the transfer case to cease delivering torque to the rear wheels unless:

1) The HI/LO range shift collar in the transfer case is really borked. In which case I can't see it moving back into a working position nicely.

2) The rear diff is borked and intermittently stops working. Again, I don't see it self-repairing.

You should right away check the fluid level in the transfer case and put in new Auto Trac II fluid. Unless the level's low, in which case just stop there and get a junkyard unit to swap in. I would not hesitate to get it on a lift and check inside the rear diff for broken bits. The danger is (and it happened to me when I grenaded my G80 while 20 miles from pavement) that if you have broken bits, they could end up jamming the guts of the diff, and either being ground finer by the rotating parts, or jamming you totally and halting you, perhaps in traffic. Scary.

I also don't have an explanation for why A4WD mode works. Without wheel slippage, the TCCM is only going to send 5% of the torque to the front wheels. This is going to burn up transfer case clutches in short order if the other torque isn't able to get to the rear wheels.

You certainly have an interesting and unique problem. Can't guarantee the fix is going to be cheap or easy, though.

 

[Krazny13]

Good morning, folks.

It can't be the switch unless you're not seeing the clue. Switch failures usually come with a Service 4WD light on the dash, or a flashing mode light on the switch. I assume your switch always stays lit on 2WD mode during these events? I can imagine a rare failure mode where the switch looks to the TCCM like you've selected "Neutral" mode (to the far right clockwise), but that mode is heavily interlocked and I can't imagine the transfer case entering neutral mode inadvertently. You'd see it on the mode light on the switch anyway.

The switch did give me issues in the beginning when I first got it, (Popping out of AWD to neutral, blinking switch light) rotated the switch a bunch to clean the contacts and the problem didn't happen again.

I see NO physical way for the transfer case to cease delivering torque to the rear wheels unless:

1) The HI/LO range shift collar in the transfer case is really borked. In which case I can't see it moving back into a working position nicely.

2) The rear diff is borked and intermittently stops working. Again, I don't see it self-repairing.

You should right away check the fluid level in the transfer case and put in new Auto Trac II fluid. Unless the level's low, in which case just stop there and get a junkyard unit to swap in. I would not hesitate to get it on a lift and check inside the rear diff for broken bits. The danger is (and it happened to me when I grenaded my G80 while 20 miles from pavement) that if you have broken bits, they could end up jamming the guts of the diff, and either being ground finer by the rotating parts, or jamming you totally and halting you, perhaps in traffic. Scary.

Alright, I'll check those out next time I'm off from work. (Hooray 2 week rolling layoffs. . . )

I also don't have an explanation for why A4WD mode works. Without wheel slippage, the TCCM is only going to send 5% of the torque to the front wheels. This is going to burn up transfer case clutches in short order if the other torque isn't able to get to the rear wheels.

I've learned as a test engineer that nothing is impossible when it comes to failure modes. . . .

You certainly have an interesting and unique problem. Can't guarantee the fix is going to be cheap or easy, though.

It never is. . . .

 

[JamesDowning]

This is a strange one indeed.

I'm wondering if a new transfer case motor might help. If it's slipping out of 2WD into Neutral, then the internal lock on the transfer case motor is either dead, or at least fubar'd.

The AWD mode will almost always work as a last resort. Since it constantly monitors the output shafts speeds, it generally does a fine job of staying locked up, even if the internal motor lock is broken.

I'm also wondering if the encoder portion of the motor has been knocked out of it's proper index somehow. It's possible that it's not fully seating into the 2WD mode position, which isn't allowing full lockup of your LO collar.

I'm curious, when it pops our of 2WD and into neutral, is that forward gear only? Does it also pop out as readily when in reverse gear? It's a quick thing to check. I'm just curious if maybe the collar has been beveled one direction by poor engagement. If it does it in only one direction, it might indicate that the spines have been beveled or otherwise worn, which is contributing to the failure.

There's also a quick way to check Bill's #2, when it's in 2WD and pops into neutral, press your brakes and rev the engine while in gear. See if the rear drive shaft spins. If the driveshaft doesn't spin, your rear diff doesn't seem suspect.

I'd try to replace the transfer case motor. If replacing the transfer case motor assembly does not fix it, I'd get a new transfer case.

 

[Krazny13]

UPDATE:

Ended up pulling the transfer case to install a new motor. Found that the Transfer Case had failed. Picked up a replacement from a junkyard and installed. Fixed the issue. Not sure why it failed, the fluid only had about 40k on it since the last change.

It had pretty much grenaded.

 

[seanpooh]

Yeah, those transfer cases are a fail. Atleast there are an abundant amount of those NVG226 at every scrapyard keeping the prices low. There is/was a brand new transfer case with the encoder motor on eBay for ~$500... I was soo tempted to get it. I'm not sure if it's still around if anyone is still looking.

My 2wd worked but there was a such a resistance in the driveline that my mpgs suffered (not that there was any to begin with) and going up hills always made the tranny downshift. So I swapped it out and I'm back to my 20-22 mpgs and hills I go up in OD with little effort.