4WD not working in 4HI

[gmcman]

I discovered this today while on saturated ground, I don't have front wheel engagement in 4HI, but I have it in A4WD. Here's a sound clip of the encoder motors while engaging 4WD. I'm not 100% on the sequence of the motors engaging, but I thought one engaged with A4WD, then the 2nd with 4HI..sounds like both engage with A4WD then a partial enagement with 4HI?

When in A4WD, it functions normally by engaging the front wheels with slippage, then releases, in 4HI, I only have 2WD.

 

[Mooseman]

Basically, this is how it works:

When you put it on A4WD, the sound you hear then is the front disconnect. Then, when you put it in 4HI, it's the encoder motor engaging the transfer case.

When you put it in A4WD and you get wheel spin, the encoder motor basically just shifts it into 4HI temporarily. From the video, sounds like it's having problems engaging or staying engaged in 4HI. Have you tried switching to 4HI while moving?

 

[gmcman]

Ok, well my issue is both motors are engaging in A4WD. I think the transfer case is engaging first.

I didn't try when moving yet.

 

[gmcman]

I stopped off at a store today, upon leaving I put trans in R and it rolled, stopped and put in D and no power in 2HI. I switched to 4HI and back to 2HI and the transfer case caught abruptly and all was good.

Does this sound like something in the switch or a bad transfer case motor.

Fluid is good and level is good.

 

[Sparky]

Almost like it was in neutral?
The switch is cheaper. Could try (with truck off) flicking the switch back and forth rapidly a bunch of times and see if it makes any difference. But if it is changing indicators to the position you select I'm not sure that's it because it at least understands what you're asking of it.

 

[gmcman]

Yeah, when I put it in Reverse, it was like it was in neutral. 2HI re engaged when I went from 2HI to 4HI and back to 2HI.

 

[BRomanJr]

Both of your issues point to a non-functional Transfer Case Motor Brake. The brake is kept energized (released) in A4WD mode to allow instant Front axle engagement when called for. In 4HI, 2HI, 2LO the brake is not energized (engaged) and supposed to hold position.

The brake is not holding 4HI, and not holding when in 2HI is allowing TC to move to neutral.
The brake is non-functional which allows A4WD to work normally.

 

[gmcman]

Both of your issues point to a non-functional Transfer Case Motor Brake.

If this is part of the encoder motor I would feel better....or is this internal?

After my drive home from work, I have a better list of details, likely reinforcing BRoman's post.

When I start the engine, I get all the lights on the 4WD selector light up momentarily, then when I select R or D, the transfer case goes into neutral, but with the 2HI light illuminated....now I believe the TC went into neutral after the engine was started. So naturally there is no movement so I put the trans in Park and I get the grinding park pawl noise until the trans stops or I take it out of park. Then I change to A4WD and I get an abrupt halt in the TC and I have power to the rear wheels. I put the selector back into 2HI and was able to drive off.

Then while in 2HI, after about 2 miles at 50 MPH, I lost power to the wheels and coasted to the shoulder. I selected A4WD and it locked in and I was able to make it home. Once home I went from 2HI, to 4HI, then 4LO, I had proper gearing in 4LO, then back to 4HI, then 2HI, I had power in all ranges but unable to test front wheels in 4HI.

I trust it's the encoder motor, but seems it could be a corroded harness at the firewall or maybe the TC...but I don't know. The motor brake sounds very plausible, first time I heard of it.

I'm curious how to check the switch and the resistance/voltages...hoping it's not the TCCM but if so, could I plug and play an 03+ TCCM without reprogramming?

 

[Mooseman]

@BRomanJr is hitting right on. I was aware of the brake in the encoder motor but I have never heard about it failing like this before.

BTW, stay away from Dorman encoder motors. They're junk.

 

[gmcman]

Sounds good, I will get an AC unit as I want to do this once.

If anyone comes across this problem, where they lose power in 2HI, I recommend shutting off the engine before going into Park or switching into A4WD or other modes as the guts are still spinning in the trans and transfer case. After the 2nd hard engagement and the terrible noise it produced, I learned to let everything stop turning first and thought that while stopped and idling that would be the case but it wasn't.

 

[gmcman]

I'll get this swapped out today or tomorrow, will keep you posted.

 

[gmcman]

I would like to have a chat with the designer who mounted the wire harness on top of the case.

So when I removed the old one, I put it in 2HI first but the shaft position was roughly 20 to 30 deg off from where the new one was. I knew not to power up the new one before installing so I raised the rear wheels off the ground and with a small rotation I was able to turn the shaft in the transfer case so it lined up with the new one.

So it likely never made it fully into 2HI as it was failing, but nonetheless it would slip out and and the new one is working.

I have 4HI now and the engagement into 2HI is more pronounced. Thanks to all for the help.

Took about 5 min to unbolt and retorque the new one, but a good 30 min releasing the wire harness without destroying the thin metal bracket.

 

[Mooseman]

Engineers. Gotta love 'em!

Glad it's fixed.