drops out of 4x4

[bogi]

I'm a new jeeper. Bought my first,97 tj 4cyl 5 spd this winter as a DD.
Bought my second, 94 yj 4 cyl 5 spd a few months later for strictly off-road.

My YJ has been dropping out of 4wd on me. Just randomly be going thru something and my buddy tells me the front wheels aren't spinning.
The dash indicator says I'm in 4 wheel and it seems to happen whether I'm in high or low.
I put it in two wheel for awhile and it goes back into 4 wheel with no problem but drops back out with no warning or indication.
Could it be a bad vacuum?

 

[jps4jeep]

CAD diaphragm on the pass side of the front axle. if it is intermittent, then it is probably a vacuum leak, if it is just not functioning, then it is junk. Google search posi lock or CAD MODS and you will see a plethora of options, some cheap, some not.

Personally if it was me, I would swap over to TJ shafts and seals, get the larger front u-joint and one piece pass. side shaft and be done until you break the puny D30 shafts.

 

[bogi]

Thanks..I'll check it out as soon as I get home. I plan on doing allot of mods to it over time.just want to be able to play as I go

 

[69jeepcj]

Just a thought here, but since you are a new jeep owner and have bought two of them, I cant help but wonder if you understand how "MOST" factory 4x4 systems work. You will have power to both front tire as long as they receive equal traction, when one front tire receives more resistance than the other, power is transferred to the other front tire and you basically have 3wheeldrive, same thing if say you have one front tire in some deep mud and the other not in it, power will be transferred to the tire in the mud as it has less resistance. So your 4x4 system may be working as it should but you are unaware that all 4 tires don't receive power at all times when using 4x4?

 

[bogi]

Yea I understand how it works. I have trucks and do allot of work on family property going thru swamps and mud cutting firewood. Just my first wranglers.
The times I refer to it not working, neither front wheel is spinning..they aren't throwing mud and I've had it verified by people watching that neither is turning.

 

[bogi]

Also I found a bad vacuum boot yesterday.haven't traced the line yet but I know it is leaking.

 

[carnuck]

that might fix the gas consumption a bit!

 

[69jeepcj]

As mentioned above, the CAD on front axe. I have had people in the past tell me my 4x4 wasn't working before, I asked them if the other side was spinning and it was, I just had to ask..

 

[Bounty__Hunter]

The boot you point to is vacuum to the Fuel Pressure Regulator on the fuel rail.

The CAD system on the front axle is easy to diagnose and service once you become familiar with it. CAD= Central Axle Disconnect.

Pull the two vacuum lines from the front axle. With the tires chocked and engine running, have somebody shift from 2wd to 4wd and back while you feel for vacuum in the two ports. Strong vacuum should switch between the two lines when changing from 2wd to 4wd and back.

Vacuum leaks under the battery are common as battery acid leaks onto the vacuum lines.

Your vacuum source is a red vacuum line from the intake manifold to the transfer case vacuum switch. The blue line from the transfer case to near the battery is a vent. There are two black lines from the transfer case vacuum switch to the front axle.

You can remove the four bolts holding the front axle disconnect on the axle and manually move the shift fork by hand. Doing so repeatedly will force moisture out of the vacuum diaphragm.

A quick easy fix to ensure you always have 4wd when you want it; Remove the disconnect from the front axle, slide the shift collar over to lock the two axleshafts together, install the disconnect upside down. Cap all vacuum ports. Now the disconnect will hold the axle locked together.

 

[bogi]

Thank you bounty hunter! I've been looking at the diff cable lock that you pull out once you've engaged 4wd to insure it stays in. I flat tow right now with a tow bar(like I said,going as my budget allows). If I use your fix will it still be ok to flat tow with the differential in neutral?

I fixed the fuel vacuum boot today.

 

[Bounty__Hunter]

Thank you bounty hunter! I've been looking at the diff cable lock that you pull out once you've engaged 4wd to insure it stays in. I flat tow right now with a tow bar(like I said,going as my budget allows). If I use your fix will it still be ok to flat tow with the differential in neutral?

You can still flat-tow with the disconnect engaged as long as you have the stock open differential. Keep in mind that your front driveshaft will turn full speed when flat-towing with the disconnect engaged. Generally not an issue but is more moving parts.

 

[bogi]

Ok guys.

I pulled the CAD off, slid the ring over and locked the shafts, topped off the gear oil and....no change.
The 4wd indicator on the dash doesn't come on now...I assume it's because I reinstalled the cover upside down and it now believes the fork is in 2wd.
I went thru everything several times...from 2 high to 4 low and only got the front axles to lock once.(I did the sharp turn on asphalt test)
The transmission is shifting...you can feel that the gears are lower when you take off in 4 low.
Also the t case bound up a couple times....was very hard to shift.
I had my wife go thru all the settings while I was under the truck and it looked to me like the linkage was fine and it was shifting.
Any ideas?
Thank you