Another Axle Disco Question

Searched but couldn't find exactly what I am experiencing so any help would be good. The hubs in my 89 are stuck in the locked position as if I were in 4wd. The dash light is on as well. If I disconnect the vacuum lines the hubs remain locked. Does this mean the fork in the axle is broken? I always thought if that happened it would get stuck in 2wd.

Thanks

Which transfer case? That would help...

Since you say it's an 89, I'm going to go out on a limb and assume that it's got the 4.0 as well.

Since you're talking about disconnect, I'm going to have to make another assumption (I really hate doing this...) and figure it's an NP231 with the D30 Disco front.

So, with all that behind us...

The NP231 shifts internally to engage the front output shaft. The axle is coupled with a vacuum actuator found on the backside of the long (passenger) tube, and vacuum to the actuator is switched with a unit on the transfer case. There are three vacuum lines, two on one side of the diaphragm and one on the other.

The single line is the "disengage" - it pulls the vacuum actuator so that the collar uncouples the aaxle shafts, and (I'd have to check) exerts a slight pull to keep the axle from accidentally engaging.

The other two work on the "engage" side - one is the vacuum supply from the tcase switch, and the other (which opens when the axle is fully engaged) supplies a vacuum signal to a switch near the surge tank under the hood, which is what turns the indicator light on and off.

I have found that, from time to time, the little actuator gets crapped up after a while, and wants to be cleaned. Do it thusly:

Place a drain pan under the vacuum actuator, and remove the (four?) bolts that hold it on. Disconnect the vacuum hoses, and remove the actuator. Clean the mating surfaces on the axle and actuator motor while you're down there. Note the position of the fork as you remove it - it will need to be there when you put it back.

Take the vacuum motor to the bench, get another drain pan, and a can of carburettor cleaner with the little red straw. Pointing everything AWAY FROM YOUR FACE, insert the straw and spray solvent into the actuator. Use the fork on the actuator to work the diaphragm back and forth. Clean both chambers, and all three ports.

Apply a LIGHT coating of RTV Black (or Red - but that Blue stuff isn't worth a damn!) or LocTite 518 Gasket Eliminator to the mating surface on the actuator, slip the fork back into position, and install. Tighten bolts to German specifications - "gudentight."

Clean the vacuum lines and reconnect. Verify operation.

I've done this a few times (got three RENIX XJ's with NP231...) and it takes me about 20 minutes to do it all. Not too bad - I just do it everytime smog rolls around automatically now, so it gets done every two years.

Of course, if you have the NP242, this means nothing, the front axle doesn't disconnect, and the lights are electrically-switched by the transfer case. How can you tell?

NP231 shiftgate bezel reads:
2HI
N
4HI
4LO

NP242 bezel reads:
2HI
4FT
N
4PT
4LO

5-90

Awesome, your assumptions are correct. I will give this a try, thanks.

5-90,
This is a GREAT write up!!! KUDOs to you!!!!!!

Thank you so much for taking the time to do it!!!!

I have been meaning to check out that "part time" light that is on, on my dash!!

CW

My '89 Cherokee Limited console reads:

2HI
4PT
4FT
N
4LO


Service manual also shows this.

Just to add .02 more to what 5-90 instructed, add a couple of oz. of gear lube to the CAD housing when you put it all back together (to replace what drained out when you opened it up). Spec is 5 oz = full.
HTH,
Jeff

bjlinma said:

My '89 Cherokee Limited console reads:

2HI
4PT
4FT
N
4LO


Service manual also shows this.

Click to expand...

True. I think he might have typo'd that one.

Have't we all.

5-90 is the man, this helped a lot. When I was cleaning things up I noted on the vaccuum line harness that you have 3 colors. Yellow, Green, and Blue. The Green applies vaccuum for 2wd and the Yellow for 4wd and the sensor for the dash light. The Blue for some reason on my rig was applying constant vacuum to the whole harness making it slow to shift after everything was cleaned up. I capped it off and now it shifts between 2wd and 4wd nice and quick. Anyone know what that Blue line is for??

Just curious. Thanks again for the help.

bjlinma said:

My '89 Cherokee Limited console reads:

2HI
4PT
4FT
N
4LO


Service manual also shows this.

Click to expand...

That's how my 01 is set up, so does this mean I have a 231, or a 242?

RizzyRong said:

That's how my 01 is set up, so does this mean I have a 231, or a 242?

Click to expand...

242

With the two 4HI settings, you should have the NP242. It's still worthwhile to crawl under and check to make sure - find the ID tag on the rear of your transfer case and you'll be sure (ignore the "J" if it's there - there were sub-models of noth transfer cases, depending on the vehicle line they went into - J for Jeep, D for Dodge, AMG for AM General/HMMWV, things like that.)

The ID tag is a round metal tag, about 2" across, usually silver with red edging, and retained by a single screw through the centre. It's usually on the back of the case, opposite the front output yoke, and may be on a raised boss (I may have mentioned this before.)

5-90

Just checked today, an you guys are right 242. Good job guys!

GADawg....is the blue line the one on the far right as your looking at it from behind?