Stuck In 4 Wheel Drive

[Raymond K Essel]

Ok, there seem to be plenty of people around here with Comanches that won't shift into 4 wheel drive, but I'm having the opposite problem.  I can't get my truck to shift back into 2 wheel drive.  For short trips I've been pulling the CAD connector off to allow the front wheels to spin independent of each other, but I'd really like to have this thing FIXED!

 

The front drive shaft does not spin freely; it's always locked in no matter where the shift lever is located.  The truck is an '87, 4.0L, automatic trans, Command-Trac.  Linkage feels tight and responsive to the lever (moves full stroke).  I believe the truck has the wrong gauge cluster in it because the "Full Time 4wd" light is constantly lit, but that isn't even an option in this truck (no Select-Trac case).  The hoses running to/from the vacuum tank behind the front bumper were in sad shape and my not have been connected properly when I got the truck.  I've replaced them, but don't know if they're going to the right places.

 

Here's my question...can I apply vacuum with my hand pump to one of the ports on the t-case vacuum switch to see if the problem is a vacuum supply issue or an internal t-case issue?  I don't know what each of the 4 colored lines on the vacuum switch is supposed to do, or if vacuum needs to be seen on multiple ports to get the t-case internals to come alive. 

 

I appreciate the help!

[Geonovast]

Once you verify that your T-case is disengaging, you should just lock the CAD and forget about it.  I think your problem is that your CAD is not unlocking, not that you're stuck in 2wd.

 

Truck parked, pull the CAD actuator off the housing, and slide the collar so that the shafts are not engaged.

 

Put the lever in the cab to 2wd.  Your front driveshaft should spin freely.  If it doesn't, there's a problem with your T-case or shift linkages.  Keep in mind that both the CAD and T-case have to be engaged for you to have 4wd.  The CAD does not lock the two front wheels together, they will still spin independently because of the differential.  An engaged CAD does not mean 4wd.

 

If it does spin freely, lock the CAD following the DIY linked in my signature.  You will thank yourself for doing so.  CAD operation is not needed for 2wd/4wd, and is not present in 92ish+ or any Full Time Jeeps.

[gogmorgo]

Did you even read the post? He's stuck in 4x4.

[Raymond K Essel]

Correct gogmorgo, stuck in 4WD.  I understand that the CAD in these things is problematic, but my understanding is that their main failure mode leaves the vehicle WITHOUT 4WD.  Ideally I'd like to know if I can separate the issue to the mechanical t-case internals vs the vacuum supply side via a hand vacuum pump on the t-case vacuum switch.  If I can pull a vacuum on the t-case vacuum switch and momentarily unlock the front drive shaft, then I'll hunt down where my vacuum supply issue is...but I don't know which vacuum switch port(s) disengage the front shaft...or if that is even a legit diagnostic method. 

[gogmorgo]

I'm fairly certain that the shifting (including engaging the front driveshaft) is purely mechanical, that is to say not dependent on vacuum at all. I can shift mine into and out of 4x4 over and over again without the engine running.

Can you shift the t-case into low range or neutral? I'm not too knowledgeable about the internal workings of the transfer case, though, so can't really help you. Have you checked the tag on the t-case to make sure you've still got an NP 231 back there?

[Raymond K Essel]

If the t-case shifting is purely mechanical, what is the vacuum switch on the t-case for?  (Seriously...honest question there.)

 

The case does shift into neutral and 4 low.  I did it without starting the vehicle soooo...guess you're right about the vacuum switch not playing a role in shifting.

 

Good thought about the case swap.  It is in fact a 231 though.  This truck is such a basket case I wouldn't have been surprised to find anything under there.

[Bobolink]

I'm siding with Geonovast here......how do you know you're stuck in 4wd? If you're determining that by the "part time" light on the panel, that's just connected to your solenoid that sends vacuum to the CAD. It is not an indication that you are actually in 4wd. It is an indication, if all is working correctly, that your CAD is locked. The only thing controlled by vacuum is the CAD itself. TC shifting is strictly mechanical. 

[Raymond K Essel]

The reason I think it's in 4WD is because the front drive shaft can't be turned by hand and when I drive the thing crow-hops like it's gonna tear itself in half.  If the t-case was actually properly in 2WD wouldn't I be able to get under the vehicle and spin the front drive shaft while the truck is stationary?

[cruiser54]

If the t-case shifting is purely mechanical, what is the vacuum switch on the t-case for?  (Seriously...honest question there.)

 

The case does shift into neutral and 4 low.  I did it without starting the vehicle soooo...guess you're right about the vacuum switch not playing a role in shifting.

 

Good thought about the case swap.  It is in fact a 231 though.  This truck is such a basket case I wouldn't have been surprised to find anything under there.

The vacuum switch on the transfer case gives vacuum to the CAD to engage/disengage it. That's all. Are you stuck in 4wd or is the CAD just staying engaged? 

[cruiser54]

Adjust your transfer case linkage, check your engine and trans mounts.

 

[Eagle]

Correct gogmorgo, stuck in 4WD.  I understand that the CAD in these things is problematic, but my understanding is that their main failure mode leaves the vehicle WITHOUT 4WD.  Ideally I'd like to know if I can separate the issue to the mechanical t-case internals vs the vacuum supply side via a hand vacuum pump on the t-case vacuum switch.  If I can pull a vacuum on the t-case vacuum switch and momentarily unlock the front drive shaft, then I'll hunt down where my vacuum supply issue is...but I don't know which vacuum switch port(s) disengage the front shaft...or if that is even a legit diagnostic method.

Since you know how to bypass or disable the CAD, you have all the tools you need. In fact, you don't even need to tinker with the CAD. Park with the rear wheels on the ground, put the transfer case into what it says is 2WD, jack up the front end, crawl underneath and try to turn the front driveshaft. If it turns, the transfer case is in 2WD. If it doesn't turn, the transfer case is in 4WD.

 

Vacuum does not actuate the transfer case. That's all mechanical. Vacuum moves the CAD slider, and vacuum turns on the light.

[yxmj]

Ok, there seem to be plenty of people around here with Comanches that won't shift into 4 wheel drive, but I'm having the opposite problem.  I can't get my truck to shift back into 2 wheel drive.  For short trips I've been pulling the CAD connector off to allow the front wheels to spin independent of each other, but I'd really like to have this thing FIXED!

 

The front drive shaft does not spin freely; it's always locked in no matter where the shift lever is located.  The truck is an '87, 4.0L, automatic trans, Command-Trac.  Linkage feels tight and responsive to the lever (moves full stroke).  I believe the truck has the wrong gauge cluster in it because the "Full Time 4wd" light is constantly lit, but that isn't even an option in this truck (no Select-Trac case).  The hoses running to/from the vacuum tank behind the front bumper were in sad shape and my not have been connected properly when I got the truck.  I've replaced them, but don't know if they're going to the right places.

 

Here's my question...can I apply vacuum with my hand pump to one of the ports on the t-case vacuum switch to see if the problem is a vacuum supply issue or an internal t-case issue?  I don't know what each of the 4 colored lines on the vacuum switch is supposed to do, or if vacuum needs to be seen on multiple ports to get the t-case internals to come alive. 

 

I appreciate the help!

 

Like said above the Cad is not mechanical and does not engage with a lever.

 

if you look at it on you axle it has a small mounting plate on our axle with a vacuum actuator.......if you want to test it it is as simple as putting a pan under it removing it and giving it a simple bench test...4 bolts and remove and label the lines...the actuators are very sensitive so when on the bench,,,,,,,put a chunk of clean hose on and suck on it....does the fork move easy both ways.......that is the first test. :thumbsup:

[yxmj]

I'm fairly certain that the shifting (including engaging the front driveshaft) is purely mechanical, that is to say not dependent on vacuum at all. I can shift mine into and out of 4x4 over and over again without the engine running.

Can you shift the t-case into low range or neutral? I'm not too knowledgeable about the internal workings of the transfer case, though, so can't really help you. Have you checked the tag on the t-case to make sure you've still got an NP 231 back there?

 

Wow.....for all your post I would think you were more aware of what was going on with your front end.......please tell us all you have A NONE CAD

[Incommando]

The reason I think it's in 4WD is because the front drive shaft can't be turned by hand and when I drive the thing crow-hops like it's gonna tear itself in half.  If the t-case was actually properly in 2WD wouldn't I be able to get under the vehicle and spin the front drive shaft while the truck is stationary?

Maybe I am misunderstanding this: If the front wheels are on the ground you should not be able to turn the front drive shaft no matter what position the transfer case is in IIRC. Even if the CAD is disconnected and the left side outer shaft could spin freely the driver's side would still be "engaged" and have the weight of the truck on it I think? (Thinking is not always my strong suit). It would take both sides of the front axle being disconnected via locking hubs or such to allow the drive shaft to spin fairly freely. Even jacking up the front so that both wheels were suspended would require you to spin the drive shaft hard enough to move a wheel via the diff on any vehicle lacking locking hubs that were unlocked. I *think* that our unit bearing front ends without such hubs means that even with CAD one axle shaft is always connected to a wheel and the front drive shaft always rotates when the vehicle is in motion no matter the t-case position or CAD activation. 

 

From what I have read this may not be common but is usually due to a linkage issue when it occurs. The t-case is never actually placed into 2hi no matter what the position of the shifter might indicate. The 231 linkage is notoriously crappy & the net offers several ways to upgrade it or replace with either home built stuff or aftermarket. Continuous body flex and or rust can also move the tunnel mounted pivot point ( #14 below) enough that the linkage does not engage the range selector properly. As 2hi is a position at the furthest point of the action it would make sense that it was one that was affected. This would also cause the 4wd light to stay activated as internally the t-case is still in 4hi. I would crawl underneath and manually manipulate the range selector ( the metal rectangle on the post that sticks out of the t-case on one end and is the terminus of the t-case side) to see if that would shift the t-case into 2hi. I don't know if this will help at all but good luck. 

 

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[cruiser54]

With a 231 and cAD, you can rotate the front drive shaft with the front wheels on the ground and the lever in 2H. 

[Incommando]

With a 231 and cAD, you can rotate the front drive shaft with the front wheels on the ground and the lever in 2H.

 

Good to know. It just makes it more likely that the t-case is not being shifted from 4hi due to a linkage issue in my mind.

[gogmorgo]

 

Wow.....for all your post I would think you were more aware of what was going on with your front end.......please tell us all you have A NONE CAD

This is completely off topic and really unnecessary, but I'll take your bait. I'm perfectly aware of how the CAD functions, a vacuum switch on the t-case triggers a vacuum solenoid at the front axle which in turn slides a collar around to engage or disengage the front passenger side axle shaft. I didn't, however, mention it once. Without the CAD, you don't get stuck in 4x4, even if it's permanently locked.

What I don't know about (as I said above) is what happens inside the t-case beyond a fairly general knowledge of form and function. I don't know what exact mechanism is used to engage the front driveshaft and turn it, I just know it isn't vacuum operated because it works without vacuum applied. I thought I'd said as much. Not sure what it has to do with the front end, though, or did you think I meant "axle" instead of "driveshaft"?

Oh, and if it makes you happy, yeah, I've got what would be a perfectly functioning CAD axle, but I've blocked off the lines to it and it's got a single piece shaft instead of the two-part. I haven't bothered putting the new seal in because I'm planning on swapping out for a non-cad axle at some point, so I'm monitoring gear oil levels. Happy?

[Raymond K Essel]

All, thank you for the many helpful responses!  I've bench-tested the CAD and it is fully operational...about the only thing aside from the clock that meets that description (I kid...it's in a heap of hurt, but it's no parts truck).  I'll inspect the t-case linkage area for rot and mis-alignment, then go through the t-case linkage adjustment process and report back.  Hopefully it's solid and simply out of adjustment!  Would be nice to fix something on this thing for free.

[COMJNUT]

The internals of a np231 are similar to a transmission, it has a collar to select 2 or 4. Maybe the shift fork has slipped off of the collar, but I have never heard of it happening on a 231. An internal "lever" of the 231 contacts the switch to move the cad vacuum motor over. As said proir, your shift linkage could be off to not shift to 2wd, that is common after going into 4wd if you don't have the adjustment nut really tight. If you can picture the 4x4 system as two seperate systems (t-case & vac system connected to it), one added onto the other, you are a lot better off. The ports on the t-case for the vacuum lines, I cannot help you with that, time for a vacuum diagram. I went a posi-lok on mine because the vacuum motors can get water in them and freeze in the winter and break the diaphram within the motor killing it from actuating. That would leave the front axle engaged or disengaged. Best thing to do is get it up in the air (all 4), take the shift motor housing off the front axle, start it, put your auto in 1st, run the t-case through the gears and have someone watching the vacuum motor on the front axle to see if it moves. It could be just the lines, the switch, the lines to the switch, the adjustment of the shift linkage (the adjustment of the shift linkage could cause both problems since the linkage adjustment is external of the t-case and the switch is internal).

[yxmj]

All, thank you for the many helpful responses!  I've bench-tested the CAD and it is fully operational...about the only thing aside from the clock that meets that description (I kid...it's in a heap of hurt, but it's no parts truck).  I'll inspect the t-case linkage area for rot and mis-alignment, then go through the t-case linkage adjustment process and report back.  Hopefully it's solid and simply out of adjustment!  Would be nice to fix something on this thing for free.

 

Before you delve too deep in to the T-case.....If you still have the cad off..... why not set it on a box or a pail and connect the vacuum lines.....have a helper engage and disengage the 4x4...see if the cad is operating as it should.

[cruiser54]

I would begin by inspecting the engine and trans mounts and adjusting the linkage per the video.

 

And once you've got the transfer case shifting, eliminate the cAD before IT disappoints you somewhere in the middle of nowhere. 

[Raymond K Essel]

Well, looks like both engine mounts are in pretty sad shape.  Not completely separated, but the passenger's side has a fissure that runs from front to back at the 2 o'clock position (looking from the front of the vehicle).  Driver's side is in mildly better shape...which means it's also bad.  Guess I'll start there! I'll probably do the trans mount too since none of these mounts are terribly expensive.