4wd engagement in a 92 XJ

Ok.. I realise that the 92 XJ's did away with the vacuum disconnect system to engage the front axle when shifting into 4wd. I am wondering what system took its place? Is the axle always engaged? Does the front axle now act like a normal axle with the hubs locked all the time? The reason I am asking is that my XJ takes a bit of time to go into 4wd after shifting the xfer-case lever into either part time or full time 4wd modes and I want to know why. If the axle was always engaged (ie: hubs always locked like on a normal 4x4 axle) then wouldn't the 4wd engagement be instantaneous?

What T Case do you have? From the way you worded your question, it seems like you have the 242. I have the 231, and when I put it in 4 part time hi or low, it has instant 4wd.

Im not too sure about the 242 though.

Mercenary said:

Ok.. I realise that the 92 XJ's did away with the vacuum disconnect system to engage the front axle when shifting into 4wd. I am wondering what system took its place? Is the axle always engaged? Does the front axle now act like a normal axle with the hubs locked all the time? The reason I am asking is that my XJ takes a bit of time to go into 4wd after shifting the xfer-case lever into either part time or full time 4wd modes and I want to know why. If the axle was always engaged (ie: hubs always locked like on a normal 4x4 axle) then wouldn't the 4wd engagement be instantaneous?

Click to expand...

I can't speak for the earlier hardware, but all 96 and newer XJs have a one piece pass side shaft (no disco). There are no lockout hubs.
With a 231 (PT) case 4WD engagement is as you say "instantaneous" as the only thing which needs to be switched is the transfer case mode. I have no experience with a 242 (FT) case and your experience may relate to the case.

A question that jumps at me is how did you defeat the disco? Did you clamp the engagement collar or replaced the axle shaft?

Mercenary said:

Ok.. I realise that the 92 XJ's did away with the vacuum disconnect system to engage the front axle when shifting into 4wd. I am wondering what system took its place? Is the axle always engaged? Does the front axle now act like a normal axle with the hubs locked all the time? The reason I am asking is that my XJ takes a bit of time to go into 4wd after shifting the xfer-case lever into either part time or full time 4wd modes and I want to know why. If the axle was always engaged (ie: hubs always locked like on a normal 4x4 axle) then wouldn't the 4wd engagement be instantaneous?

Click to expand...

They still use the vacuum disco 93 so the slow 4wd is caused by a vacuum leak.

Ok, I was under the impression that Chrysler did away with the vacuum disco system in 91. I thought all models from 92 up had no vacuum disconnects. I don't have vacuum discos on my 92. I have the 242 x-fer case as well.

My XJ is definetly ACTING like it has vacuum disconnects. It takes a bit of time to engage and disengage 4wd when I shift into 4wd.

So...the way I see it is that ALL 92 XJ's (or 96's) and up have one piece axle shafts. These axles are permanently attached to the wheels, right? (ie: no hubs) So..theoretically, when you throw the lever into 4wd, no matter what x-fer case you have, you should be in 4wd, right?

You don't have vacuum discos with the 242. How's your t-case fluid? Old, burnt, or low?

It all depends on if you have commad track or select track.
Command track uses the disco (231) Select-Track (242) don't.

langer1 said:

It all depends on if you have commad track or select track.

Click to expand...

You weren't referring to my post were you? Because the 242 IS the "Selec-Trac" t-case.

What difference would the condition of the oil in the t case have to do with anything? If it is a mechanical linkage, and the lever actually moves into the desired position when engaging 4wd, you should be in 4wd as soon as you put the lever into 4wd mode.

Let me clarify. I don't have a problem actually moving the lever into 4wd part time/full time etc, etc. The t case shifts fine into all modes, but it can take a few minutes to actually engage/disengage 4wd.

Here is a scenario that happened the other day...We had a great deal of snow fall in a couple of hours. I attempted to back into my normal parking spot here at my house and was unable to do so due to the great deal of snow and ice that had built up. I shifted into 4wd part time and attempted to back into my parking spot again. All I heard was a grinding noise coming from the front end and the 4wd P/T indicator light kept flickering until I came to a complete stop. I then heard a clunk sound from the front end, the indicator light stayed on and I was able to back up in 4wd as normal. The grinding noise I heard was similar to what is heard if you grind gears in a manual transmission. I can't describe it better than that. Like I said, my XJ is acting like it has vacuum disconnects but I know that it doesn't.

Mercenary said:

What difference would the condition of the oil in the t case have to do with anything? If it is a mechanical linkage, and the lever actually moves into the desired position when engaging 4wd, you should be in 4wd as soon as you put the lever into 4wd mode.

Let me clarify. I don't have a problem actually moving the lever into 4wd part time/full time etc, etc. The t case shifts fine into all modes, but it can take a few minutes to actually engage/disengage 4wd.

Here is a scenario that happened the other day...We had a great deal of snow fall in a couple of hours. I attempted to back into my normal parking spot here at my house and was unable to do so due to the great deal of snow and ice that had built up. I shifted into 4wd part time and attempted to back into my parking spot again. All I heard was a grinding noise coming from the front end and the 4wd P/T indicator light kept flickering until I came to a complete stop. I then heard a clunk sound from the front end, the indicator light stayed on and I was able to back up in 4wd as normal. The grinding noise I heard was similar to what is heard if you grind gears in a manual transmission. I can't describe it better than that. Like I said, my XJ is acting like it has vacuum disconnects but I know that it doesn't.

Click to expand...

And like I said it's a problem with the front disco or a vacuum leak.
There is nothing up front that could act/sound like that accept a disco. Someone could have converted it to select track and kept the vacuum disco.

why don't you just look at the axle? It will take 2 minutes to know if you've got a vac disco or not. Kind of hard to miss the big bulky thing on top of the passenger side shaft with vac hoses going to it.

I have looked at the axle. I've looked long and hard for some sort of vacuum disconnect system on the front of my jeep. It isn't there.

Could the T-case itself be the issue here? I mean, is there some sort of electronic engagement device similar to what the Chevy trucks have? Its almost like something has to mesh up centrifically (sp?) before 4wd will engage on my Jeep. Might it have something to do with the center differential that allows the 242 case to have the part time and full time 4wd modes?

Ok...I just answered my own question here. This is something that I found on another site...


UNIT INSTALLATION AND TROUBLE SHOOTING GUIDE



NEW VENTURE 242 TRANSFER CASE



IMPORTANT- PLEASE READ CAREFULLY


Before attempting any diagnostic work or trouble shooting on the transfer cases, make sure that the tire pressures and circumference are all the same. Do not just compare tire sidewall labels; you must measure each tire around the center of the tread. A stagger gauge (RSG Part # 910-82017) will let you do this with the vehicle on the ground in 5 minutes. The tires must match in size to ¼” (.250), outside circumference, if they do not sell the customer on a new set of tires and measure them again. Mismatched tire sizes and pressures will fail the differential in these units very quickly and will cause the unit to be unable to shift out of 4 wheel drive back to 2 wheel drive.


Transfer case will not release from 4WD even when shift lever is put into 2WD- this is caused by the unit getting spline locked internally due to mismatched tire sizes or pressure. The unit will release if run on a lift because the wheels are not turning on the ground and tire size does not matter if all 4 wheels are in the air. Measure the tires with a tape around the middle of the tread or a stagger gauge and make sure they are all within ¼” (.250) and make sure all tire pressures are equal. Do not remove the unit for this problem; you will only waste your valuable time.


Transfer case will not shift standing still- this is normal and correct. The shift fork is spring loaded and the front and rear tires must be moving at the same speed in order for the unit to shift.


Proper operation in the different ranges- Make the customer aware that this unit can be operated in the fulltime position on any surface, wet or dry pavement. Part-time and Low must only be used in mud, deep snow, or sand.


On installation, make sure the transfer case shift lever is facing up towards the floor of the vehicle on 99 and up models. On 1987-98 vehicles, the transfer case lever should face down away from the floor.


Many states now require dynamic emissions tests on dynamometer. This unit cannot be tested on a dyno without immediate failure to the internal transfer case differential. If this unit is used on a dyno with the front wheels stationary, the internal differential pinions will rotate at approximately 15,000 RPM. This immediately wipes out the differential and causes other internal damage to the transfer case. The same thing will happen if the vehicle is towed with the front wheels on a dolly. Make sure to note this on your work order and make sure the customer signs acknowledging that there is no warranty for this type of failure.


Fill this unit with RSG-530-GM fluid and change fluid every 12,000 miles.

This here is a useful tidbit of information. I had no idea that the 242 shift fork is spring loaded and it only engages 4wd when the front tire speed matches the rear tire speed (all things being equal). I knew that all 4 tires had to be the same diameter and at the same psi, but it does explain the delay in going into and out of 4wd. I also had no idea that you couldn't shift the 242 into 4wd without being moving a bit. I was under the impression that it was a direct mechanical linkage and once you shifted into 4wd, you were IN 4wd. I guess it would be possible to shift into 4wd while at a stand still IF the shift fork just happened to line up on the splines.

So, all and all, this sets my mid at ease.

It will also take a long time to engauge if low on fluid.
Thing is though the t-case is in almost in the back seat and the noise you said is comming from the front.
Also if all 4 wheels have to be going the same speed how would you put it in 4wd if you were already stuck?
One more thing your t-case has a netural for towing and dyno testing.

I think 4wd will engage when you are stuck as you try to rock the truck back and forth attempting to extricate yourself. The couple of times I have had to shift into 4wd when stuck, the t-case always seemed to engage 4wd just as I was getting on the throttle or when I was getting off the throttle. That would explain that shift fork spring pushing against the shift fork constantly and then clicking into place as soon as the splines lined up. I don't think the front wheels have to be going the EXACT same speed as the rear wheels. I mean, if they were going the same speed and the splines between the two shafts were just a little off, then 4wd would never engage.

I just cannot see how being low on fluid would influence the speed at which your 4wd would engage. I can see how this would affect an automatic transmission as the fluid is directly used in the process. I was under the impression that the fluid in a x-fer case is there for lubrication only. I could be totally wrong about this though.