Hey guys i am new around here and have some questions! The 4x4 will not engage on my truck. i understand the vacuum operated system and suspect that this is where to start on fixing it. however, my ABS and parking brake light are always on as well. is there anyway that the two could be connected? when i put the truck into 4H there is no change in the steering and the lights do not illuminate. in 4L still no lights or steering change but it does go into low range. any help you could offer on this would be great! also if anyone has experience trouble shooting the vacuum system or has a diagram i would appreciate the insight! thanks in advance guys.Also not sure how to do a sig but here is the info:2001 2500 5.9 SO w/5 spd. new VP44 and FRRP w/ big-line kit from DAP. everything else is stock

I think this will get you far. http://articles.mopar1973man.com/general-cummins/39-transmission-systems/80-central-axle-disconnect-cad-system-troubleshooting I never looked much into the ABS issues but probably unrelated, though those lights being on is very common.

thanks that should be exactly what i needed! i am new to diesels and am learning a ton from this site

Yeah Welcome to the site and hope that fixes the problem or allows you to fix it. Don't be afraid to ask anything or jump into threads that are already going if you have something to say. The more input on issues that seem unresolved, the better.

The vacume activated center axle disconnect (CAD) is troublesome & was omitted I think after 2002 (my 01.5 has it). They can get stuck or the diaphram rupture. Some people have put cable activitators in there. The valve on the transfer case can fail too.

I am out of town on business but when I get home I will be jumping into that. Is the CAD expensive? I am considering just pulling and replacing it all for my own peace of mind

I'd put the money toward a cable actuator kit instead. You eliminate all the vacuum and use a push/pull cable. You can also select 4 low with your transfer case and not pull the cable and have low range 2 wheel drive.

How expensive are the cables? It's cold and rainy here today but I did crawl under for a minute and the red vacuum line that runs from the firewall to the hard lines has a big crack in it. Seems like a likely candidate

If it's just a cheap vacume line, fix it. It's gotta be way easier & cheaper than a cable kit... To install a cable kit, the cable must be threaded into the cab & the actuator assembly on the axle taken off & replaced with the cable unit.

I tend to agree with the guys here... I would check over the vacuum lines and the CAD vacuum motor first before investing in a expensive cable kit.

well guys i appreciate all of the help but i have to admit that i am an idiot. aside from the cracked red vacuum line, wich is now fixed, the problem with my 4x4 was.....it was disconnected . that diagram was very useful in tracking down the grey supply line. when i found it, it was just pulled off of the T. it engages and disengages just fine now! thanks to everyone for the help, Problem solved!

YEAH!!

I am having the same problem with my truck. I replaced the CAD last year to no avail and I just replaced the switch on the transfer case today as I finally discovered the prongs on the old one were MIA. I still have no 4wd but the light comes on when I select 4H or 4L on the shifter so that should mean I have vacuum there right??? Is it possible that I have the shifter fork in backwards causing this to happen??? I hope it's nothing more serious than that!!!

im not sure how the forks go in but if the light is on then the vacuum is moving the lever. how do you know that it is not engaging when the light comes on?

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also i was just rereading mikes trouble shooting article, are you sure that they gave you the right fork? apparently there were two different styles

If I remember correctly I used the original fork and just replaced the actuator. I know it's not working because I almost got stock in my yard yesterday after replacing the switch.

Someone correct me if I'm wrong but I believe that there are contact points on the fork that can wear out. If they were to wear far enough I can see them not engaging properly

Are you positive your vaccum lines are hooked up coreectly? If you have a doubt, just switch them around real quick at the actuator on the axle it wont hurt anything and if it doesnt work than you can switch them right back around. This is assuming you know for a fact youve got vaccum TO the actuator....

Someone correct me if I'm wrong but I believe that there are contact points on the fork that can wear out. If they were to wear far enough I can see them not engaging properly

If I remember, there are little plastic things that go on the tips of the fork that slide over the sliding collar. I'd imagine you are correct.

If I remember, there are little plastic things that go on the tips of the fork that slide over the sliding collar. I'd imagine you are correct.

The kit came with the new plastic ears when I put the new actuator on. I have vacuum at the CAD and it SHOULD mean the actuator is sliding when I move the shifter because the 4x4 light comes on, right?

Right, the 4x4 light is switched by the actuator physically hitting the actual switch, so its bulletproof. But its kinda reverse that because it is normally closed (switch is on), meaning when the actuator hits it, it opens the circuit and the light goes out. You might try jacking the passenger side front tire up and it shouldn't spin if you are in 4wd, then go take it out and it should spin.

The kit came with the new plastic ears when I put the new actuator on. I have vacuum at the CAD and it SHOULD mean the actuator is sliding when I move the shifter because the 4x4 light comes on, right?

Right, the 4x4 light is switched by the actuator physically hitting the actual switch, so its bulletproof. But its kinda reverse that because it is normally closed (switch is on), meaning when the actuator hits it, it opens the circuit and the light goes out. You might try jacking the passenger side front tire up and it shouldn't spin if you are in 4wd, then go take it out and it should spin. The passenger side axle is cut where the CAD thing is and it has splines on each side of the "cut" and the CAD thing just slips a collar over the splines, interlocking them. It does this so the driver side wheel will just spin the passenger axle instead of the driveshaft when in 2wd, saving u-joints, etc.. I'm just throwing all this out there so you can picture the operation so you can see why jacking up the passenger front tire is the easiest diagnostic method.