1987 Comanche Stuck In 4 Wheel Drive

[Raymond K Essel]

Hi everyone.  First time poster here.  I bought my Comanche a few months ago from a guy who bought it with the intention of fixing everything up, but then I guess lost interest/lacked knowledge, and wound up unloading it for cheap.  I've been working through many of the problems he avoided (and some of the ones he fixed... ...) but one so far has left me baffled. 

 

The thing is stuck in 4 wheel drive!  It has the NP231 (Command Trac) and when I start the vehicle it shows 4WD on the dash, plus, when I drive it around the block I can definitely feel crow-hop going on.  With the t-case selector in 2wd it's in 4wd.  With the selector in 4wd high, it's in 4wd.  I think it switches to 4 low with the selector, but haven't really checked that.  Regardless, the case won't switch into 2wd. 

 

In order to get the truck home from where I bought it I tried everything I could to get it into 2wd.  I went in reverse and backed up, I tried turning while in reverse, doing 30 I dumped the trans into neutral, played with the t-case lever, and then back into drive, I got under the truck and manually moved the adjuster, I banged on the adjuster with a rubber mallet to make sure it was making full travel (I think it was)...I've still got nothing.  In order to get the truck home from where I bought it I wound up pulling the vacuum coupler off the CAD which turned off the dash 4WD light and eliminated crow-hop (it was definitely in 2WD) and then I drove it 150 miles home.  When I got home I tried connecting the CAD vacuum once again to see if it shook free of 4WD and even after all that it still hadn't. 

 

I took the CAD fork assembly off and pulled vacuum on each of the ports to see if it were hanging up somewhere and it moves freely in both directions.  I think part of the problem is I don't fully understand what happens when I pull the t-case lever.  Obviously the front drive shaft becomes engaged, but what activates the CAD?  What switches the vacuum from one side of the CAD diaphragm to the other?  Where is that valve/switch/doo-hickey located? Where does the 4WD dash light signal come from?  I obviously interrupted it by removing the vacuum coupling from the CAD, but the mechanicals in the t-case are still in 4WD orientation right?  Can someone supply a play-by-play of whats supposed to happen when I throw that t-case lever into 4-hi?  Or at least a list of things I may want to check.

 

Anyway, this general lack of 4WD understanding is keeping me from driving my Comanche!  So...any help is much appreciated.  Thanks guys!

[Geonovast]

Click the CAD link in my signature, and it should help describe how the stupid thing words, and how to permanently bypass it.  There's no reason it can't stay locked forever.

 

My main concern is, what makes you think it's stuck in 4wd?  The CAD systems disengage 4wd in two locations.  So unless you know for sure that your T-case is sticking, you're better off locking the thing.  If you're going off the light... well, that's less than dependable.

 

With the shifter in 2wd, can you get under the truck and rotate the front driveshaft by hand?

[87manche1]

Yep to geonovast, try that first but after there is a spring inside the transfer case that forces the sprocket back into 2wd and usually they lose they're shape after yrs that y the backup trick works.look at link 3rd pic u will see it in the middle http://www.greatlakes4x4.com/showthread.php?t=208056

[Raymond K Essel]

Wow, man I am so sorry guys!  I had to move after I posted back in March and that really disrupted my wrenching time!  Just to fill you in on how things are going...

 

The front drive shaft can be spun by hand when the vehicle is both off and running.  After much work with the idle I was finally about to drive it around yesterday (~15 miles total) and it is definitely NOT in 4 wheel drive, though the dash reports I am.  I don't know whats going on with that yet.  Also, from previous experience (I had an '89 XJ about 10 years ago) the Full-time 4wd offered by the Selectrac case lights a green 4wd light, while the part-time offered by the Commandtrac lights a yellow 4wd light.  My Comanche has the Commandtrac, but a green 4wd symbol is (erroneously) lit on the dash.  Am I off base with this memory?  Maybe it's a swapped dash.  Judging from what I've seen on this vehicle so far nothing would surprise me. 

 

I haven't yet done that CAD modification, but I am planning to.  I'm still working on the things that are keeping it from being road-worthy.  At this point that involves figuring out why the 12 volts at my "near the spare tire" connector isn't getting all the way to the brake light bulbs. I look forward to the day the truck operates as it was designed to!

[ParadiseMJ]

Have you crawled under the Jeep to make sure the transfer case linkage is attached properly?  The dash light is operated by a vacuum switch (located on the passenger side fender, by the firewall...it's blue.  When the lever is pulled, into 4HI OR 4LO, considering the linkage is attached and adjusted properly, the transfer case switch opens and sends vacuum to the dash light vacuum switch and trips the switch...turning the light on.

 

If you're having trouble with the brake lights:

• check to see if the brake light switch is firmly attached.
• Check to see if you have trailer wiring, funky trailer wiring

[Raymond K Essel]

Regular Guy, thank you for the 4wd light explanation!  Next time I take a look at the engine bay I'll check out that switch.  The whole "how it happens" thing has been a little mysterious to me so far.  This helps a lot!

 

As for the brake lights: I believe the brake light switch is firmly attached.  I found the connector near the spare tire and probed the input side while someone applied the brake.  I've got battery voltage on the grey/white and brown wires with the brake pedal depressed, and 0V when the brake pedal is not activated.  The really confusing part is my turn signals work, which uses the same filament in the tail light bulb as the brake light, right?  The sockets look a little melted and nasty so maybe they're damaged in a way that only affects the brake input circuit...tail lights and turn signals unaffected.  Seems like kind of a long shot, especially on all 4 bulbs, but I'm not sure what wire at the socket is responsible for brake light signal, so it's tough to check at the socket for B+.  The color labels in my Haynes manual don't match my specific vehicle.  I think I might replace one socket (~7 bucks) and if that works do the rest.