98 Jimmy stuck in 4WD - Can't go to 2HI

[loots42]

I think I've read all the relevant post on this topic but still uncertain as to what my solution may be.

It's a 98 Jimmy with 3 button system. If it's in 2HI, it shifts perfectly to 4HI. I can then shift to 4LO, and back again to 4HI. But it does not then shift back to 2HI. Eventually, after rocking the truck and pressing the 2HI button, it will shift back. Sometimes takes 10+ minutes of trying. So you can imagine, I hate to use the 4WD, but sometimes need it.

Here's the thing. I can hear the TC shifting as I press the button, but then appears to shift back again and end up staying in 4HI. I read a post about the encoder motor on the TC being bad. But it shift fine between Hi and Lo. Is there really a "shift" involved between 4HI and 2HI? Is this shift really one to change the vacuum position, to de-activate the vacuum to the front diaphram up front?

I jacked up the front end of the truck when it was stuck in 4wd and with the engine off, I am able to spin the front wheel. Started the truck up, vacuum was applied and the wheel would no longer spin.

I've been trying to figure out what's wrong with this for a long time. The dealer said they'd recommend replacing everything in the system. About $1800. No way I'm spending that. Thanks for any advise you may have.

[MT-2500]

First thing check fluid level in transfer case.

Do not operate it in 4W on dry payment.
Normal driving or normal 4W you do not need 4W low.

Is your tires a matched set?

First try backing up shift to neutral and let it roll forward.
If that helps it may be just binding up from driving on dry payment.
Post back if that helps.

[loots42]

Fluid level is ok. Yup, I don't drive it on dry pavement. But people must think I'm nuts because I drive in the snow covered edge of the road instead of the dry track marks when its suck in 4wd.

I've tried all methods of shifting it. My driveway is shaded so always stays snow covered. I try backing up, then rolling forward as you suggested, rolling forward and turning left or right, etc. Nothing.

But since I'm in 4HI, the does the transfer case even need to shift to go to 2HI. The front drive axle always is engaged, correct? Then it's just a matter of the front axle being engaged or disengaged.

Is it the transfer case encoder motor that controls the vacuum to the front axle?

Thanks.

[MT-2500]

The encoder motor shifts transfer case in and out of 4W
Vacuum is seperate from encoder motor.

In 4W the front drive shaft is engauged.

On yours if it does not shift out of 4W to 2W or show 2W on lights check transfer case and front drive shaft for locking in and out.

http://www.automotiveforums.com/vbul...d.php?t=572914

Check for codes on yours by grounding pin 13 on diagnostic connecter and watching the shift button lights.
Post back codes/button flashes.

[loots42]

Ok, I'm still confused.

The link in the previous post indicates that the front drive shaft is always active, 4WD or 2WD. So the transfer case is always engaged, either in High or Lo. So it seems the only different between 4HI and 2HI is that vacuum is supplied to the diaphram under the battery, which in turns pulls the cable to the front axle and engages 4WD.

This is indeed what I find on my vehicle. It is stuck in 4HI, but when the engine is off, the front axle is not engage due to a lack of vacuum being supplied.

So I think my question is this: What happens when you shift from 4HI to 4 LO that signals the vacuum to NOT be supplied to the front axle?

[MT-2500]

From 4W high to 4W low the front axel and vacuum to should remain the same or locked in.
If shifted to 2W the vacuum switch on transfer case should shut off vacuum to front axel
The gear ration in trasfer case from high to low 4W is the only thing that should change on 4W High to 4WLow
The encoder motor moves the transfer case from 4Wh to 4WL position.
Giving you a low gear ratio.

[loots42]

Stupid typo in my last post.

The question I was trying to ask is:

What happens when you shift from 4HI to 2WD that signals the vacuum to NOT be supplied to the front axle?

[MT-2500]

The vacuum switch on the transfer case controls engine vacuum to front axel

[loots42]

So I just checked the TC fluid level. It's right where it should be.
And I can see the front axle vacuum actuator under the battery tray pull the cable out as I start the vehicle, and it releases when I turn the vehicle off, and vacuum goes away.

Any other ideas?

[MT-2500]

Did you check for codes?
Make sure the transfer case encoder motor is shifting from 4W to 2W.

A facory repair manual or.
http://www.alldata.com/products/diy/index.html

Will explain what is what,

[loots42]

So are you saying the TC does shift from 4H to 2H? By shift do you mean actually engage gears, because I believe the front shaft is engage in 2H the same as it is in 4H?

Or is there some sort of shift in the transfer case refering to a position that signals the vacuum to no longer be applied to the front axle actuator, when in the 4W positions (4H and 4LO)

[MT-2500]

Checko for codes and post back codes.

In 4WH and 4WL the front axel should have vacuum and be be engauged.

If transfer case is shifting to 2W there is a vacuum switch on the transfer case that should shut off vacuum to front axel and the transfer case computer will turn off all electrical circuits for 4W.
In 2W the 2W button should light up and stay on.
Does yours do that?

[loots42]

Let me ask another question.

All electronics and sensors aside, is being in 4HI with out the front axle being engaged, the same as being in 2HI?

If so, I can just unhook the actuator under the battery and safely drive the truck, even with the switch inside reading 4HI

[MT-2500]

Originally Posted by loots42

Let me ask another question.

All electronics and sensors aside, is being in 4HI with out the front axle being engaged, the same as being in 2HI?

If so, I can just unhook the actuator under the battery and safely drive the truck, even with the switch inside reading 4HI

It is always best to fix it right.

[Mightiestmike]

HELP! I am having the EXACT SAME ISSUE! I could swear I could have wrote the description to the problem!

This is my First 4x4 vehicle and I don't know too much about it.

The one thing that worried me about what i've read is, "Don't drive on dry pavement in 4W?" why not? I've never been told anything about this... I don't make it a habit to drive on dry pavement in 4W as it is quite un-necessary, but it happens when there is a part of the road that is dry, or plowed well... what can that do to the truck?

How did loots42 fix his truck?!

Please Help.